Version 2, June 1991
Copyright (C) 1989, 1991 Free Software Foundation, Inc. 59 Temple Place, Suite 330, Boston, MA 02111, USA Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed.
The licenses for most software are designed to take away your freedom to share and change it. By contrast, the GNU General Public License is intended to guarantee your freedom to share and change free software--to make sure the software is free for all its users. This General Public License applies to most of the Free Software Foundation's software and to any other program whose authors commit to using it. (Some other Free Software Foundation software is covered by the GNU Library General Public License instead.) You can apply it to your programs, too.
When we speak of free software, we are referring to freedom, not price. Our General Public Licenses are designed to make sure that you have the freedom to distribute copies of free software (and charge for this service if you wish), that you receive source code or can get it if you want it, that you can change the software or use pieces of it in new free programs; and that you know you can do these things.
To protect your rights, we need to make restrictions that forbid anyone to deny you these rights or to ask you to surrender the rights. These restrictions translate to certain responsibilities for you if you distribute copies of the software, or if you modify it.
For example, if you distribute copies of such a program, whether gratis or for a fee, you must give the recipients all the rights that you have. You must make sure that they, too, receive or can get the source code. And you must show them these terms so they know their rights.
We protect your rights with two steps: (1) copyright the software, and (2) offer you this license which gives you legal permission to copy, distribute and/or modify the software.
Also, for each author's protection and ours, we want to make certain that everyone understands that there is no warranty for this free software. If the software is modified by someone else and passed on, we want its recipients to know that what they have is not the original, so that any problems introduced by others will not reflect on the original authors' reputations.
Finally, any free program is threatened constantly by software patents. We wish to avoid the danger that redistributors of a free program will individually obtain patent licenses, in effect making the program proprietary. To prevent this, we have made it clear that any patent must be licensed for everyone's free use or not licensed at all.
The precise terms and conditions for copying, distribution and modification follow.
NO WARRANTY
If you develop a new program, and you want it to be of the greatest possible use to the public, the best way to achieve this is to make it free software which everyone can redistribute and change under these terms.
To do so, attach the following notices to the program. It is safest to attach them to the start of each source file to most effectively convey the exclusion of warranty; and each file should have at least the "copyright" line and a pointer to where the full notice is found.
one line to give the program's name and an idea of what it does. Copyright (C) 19yy name of author This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111, USA.
Also add information on how to contact you by electronic and paper mail.
If the program is interactive, make it output a short notice like this when it starts in an interactive mode:
Gnomovision version 69, Copyright (C) 19yy name of author Gnomovision comes with ABSOLUTELY NO WARRANTY; for details type `show w'. This is free software, and you are welcome to redistribute it under certain conditions; type `show c' for details.
The hypothetical commands `show w' and `show c' should show the appropriate parts of the General Public License. Of course, the commands you use may be called something other than `show w' and `show c'; they could even be mouse-clicks or menu items--whatever suits your program.
You should also get your employer (if you work as a programmer) or your school, if any, to sign a "copyright disclaimer" for the program, if necessary. Here is a sample; alter the names:
Yoyodyne, Inc., hereby disclaims all copyright interest in the program `Gnomovision' (which makes passes at compilers) written by James Hacker. signature of Ty Coon, 1 April 1989 Ty Coon, President of Vice
This General Public License does not permit incorporating your program into proprietary programs. If your program is a subroutine library, you may consider it more useful to permit linking proprietary applications with the library. If this is what you want to do, use the GNU Library General Public License instead of this License.
Most of the GNU Emacs text editor is written in the programming language called Emacs Lisp. You can write new code in Emacs Lisp and install it as an extension to the editor. However, Emacs Lisp is more than a mere "extension language"; it is a full computer programming language in its own right. You can use it as you would any other programming language.
Because Emacs Lisp is designed for use in an editor, it has special features for scanning and parsing text as well as features for handling files, buffers, displays, subprocesses, and so on. Emacs Lisp is closely integrated with the editing facilities; thus, editing commands are functions that can also conveniently be called from Lisp programs, and parameters for customization are ordinary Lisp variables.
This manual attempts to be a full description of Emacs Lisp. For a beginner's introduction to Emacs Lisp, see An Introduction to Emacs Lisp Programming, by Bob Chassell, also published by the Free Software Foundation. This manual presumes considerable familiarity with the use of Emacs for editing; see The GNU Emacs Manual for this basic information.
Generally speaking, the earlier chapters describe features of Emacs Lisp that have counterparts in many programming languages, and later chapters describe features that are peculiar to Emacs Lisp or relate specifically to editing.
This is edition 2.5.
This manual has gone through numerous drafts. It is nearly complete but not flawless. There are a few topics that are not covered, either because we consider them secondary (such as most of the individual modes) or because they are yet to be written. Because we are not able to deal with them completely, we have left out several parts intentionally. This includes most information about usage on VMS.
The manual should be fully correct in what it does cover, and it is therefore open to criticism on anything it says--from specific examples and descriptive text, to the ordering of chapters and sections. If something is confusing, or you find that you have to look at the sources or experiment to learn something not covered in the manual, then perhaps the manual should be fixed. Please let us know.
As you use the manual, we ask that you mark pages with corrections so you can later look them up and send them in. If you think of a simple, real-life example for a function or group of functions, please make an effort to write it up and send it in. Please reference any comments to the chapter name, section name, and function name, as appropriate, since page numbers and chapter and section numbers will change and we may have trouble finding the text you are talking about. Also state the number of the edition you are criticizing.
Please mail comments and corrections to
bug-lisp-manual@gnu.org
We let mail to this list accumulate unread until someone decides to
apply the corrections. Months, and sometimes years, go by between
updates. So please attach no significance to the lack of a reply--your
mail will be acted on in due time. If you want to contact the
Emacs maintainers more quickly, send mail to
bug-gnu-emacs@gnu.org.
Lisp (LISt Processing language) was first developed in the late 1950s at the Massachusetts Institute of Technology for research in artificial intelligence. The great power of the Lisp language makes it ideal for other purposes as well, such as writing editing commands.
Dozens of Lisp implementations have been built over the years, each with its own idiosyncrasies. Many of them were inspired by Maclisp, which was written in the 1960s at MIT's Project MAC. Eventually the implementors of the descendants of Maclisp came together and developed a standard for Lisp systems, called Common Lisp. In the meantime, Gerry Sussman and Guy Steele at MIT developed a simplified but very powerful dialect of Lisp, called Scheme.
GNU Emacs Lisp is largely inspired by Maclisp, and a little by Common Lisp. If you know Common Lisp, you will notice many similarities. However, many features of Common Lisp have been omitted or simplified in order to reduce the memory requirements of GNU Emacs. Sometimes the simplifications are so drastic that a Common Lisp user might be very confused. We will occasionally point out how GNU Emacs Lisp differs from Common Lisp. If you don't know Common Lisp, don't worry about it; this manual is self-contained.
A certain amount of Common Lisp emulation is available via the `cl' library See section `Common Lisp Extension' in Common Lisp Extensions.
Emacs Lisp is not at all influenced by Scheme; but the GNU project has an implementation of Scheme, called Guile. We use Guile in all new GNU software that calls for extensibility.
This section explains the notational conventions that are used in this manual. You may want to skip this section and refer back to it later.
Throughout this manual, the phrases "the Lisp reader" and "the Lisp printer" refer to those routines in Lisp that convert textual representations of Lisp objects into actual Lisp objects, and vice versa. See section Printed Representation and Read Syntax, for more details. You, the person reading this manual, are thought of as "the programmer" and are addressed as "you". "The user" is the person who uses Lisp programs, including those you write.
Examples of Lisp code appear in this font or form: (list 1 2
3). Names that represent metasyntactic variables, or arguments to a
function being described, appear in this font or form:
first-number.
nil and t
In Lisp, the symbol nil has three separate meanings: it
is a symbol with the name `nil'; it is the logical truth value
false; and it is the empty list--the list of zero elements.
When used as a variable, nil always has the value nil.
As far as the Lisp reader is concerned, `()' and `nil' are
identical: they stand for the same object, the symbol nil. The
different ways of writing the symbol are intended entirely for human
readers. After the Lisp reader has read either `()' or `nil',
there is no way to determine which representation was actually written
by the programmer.
In this manual, we use () when we wish to emphasize that it
means the empty list, and we use nil when we wish to emphasize
that it means the truth value false. That is a good convention to use
in Lisp programs also.
(cons 'foo ()) ; Emphasize the empty list (not nil) ; Emphasize the truth value false
In contexts where a truth value is expected, any non-nil value
is considered to be true. However, t is the preferred way
to represent the truth value true. When you need to choose a
value which represents true, and there is no other basis for
choosing, use t. The symbol t always has the value
t.
In Emacs Lisp, nil and t are special symbols that always
evaluate to themselves. This is so that you do not need to quote them
to use them as constants in a program. An attempt to change their
values results in a setting-constant error. The same is true of
any symbol whose name starts with a colon (`:'). See section Variables That Never Change.
A Lisp expression that you can evaluate is called a form. Evaluating a form always produces a result, which is a Lisp object. In the examples in this manual, this is indicated with `=>':
(car '(1 2))
=> 1
You can read this as "(car '(1 2)) evaluates to 1".
When a form is a macro call, it expands into a new form for Lisp to evaluate. We show the result of the expansion with `==>'. We may or may not show the result of the evaluation of the expanded form.
(third '(a b c))
==> (car (cdr (cdr '(a b c))))
=> c
Sometimes to help describe one form we show another form that produces identical results. The exact equivalence of two forms is indicated with `=='.
(make-sparse-keymap) == (list 'keymap)
Many of the examples in this manual print text when they are
evaluated. If you execute example code in a Lisp Interaction buffer
(such as the buffer `*scratch*'), the printed text is inserted into
the buffer. If you execute the example by other means (such as by
evaluating the function eval-region), the printed text is
displayed in the echo area. You should be aware that text displayed in
the echo area is truncated to a single line.
Examples in this manual indicate printed text with `-|',
irrespective of where that text goes. The value returned by evaluating
the form (here bar) follows on a separate line.
(progn (print 'foo) (print 'bar))
-| foo
-| bar
=> bar
Some examples signal errors. This normally displays an error message in the echo area. We show the error message on a line starting with `error-->'. Note that `error-->' itself does not appear in the echo area.
(+ 23 'x) error--> Wrong type argument: number-or-marker-p, x
Some examples show modifications to text in a buffer, with "before" and "after" versions of the text. These examples show the contents of the buffer in question between two lines of dashes containing the buffer name. In addition, `-!-' indicates the location of point. (The symbol for point, of course, is not part of the text in the buffer; it indicates the place between two characters where point is currently located.)
---------- Buffer: foo ----------
This is the -!-contents of foo.
---------- Buffer: foo ----------
(insert "changed ")
=> nil
---------- Buffer: foo ----------
This is the changed -!-contents of foo.
---------- Buffer: foo ----------
Functions, variables, macros, commands, user options, and special forms are described in this manual in a uniform format. The first line of a description contains the name of the item followed by its arguments, if any. The category--function, variable, or whatever--is printed next to the right margin. The description follows on succeeding lines, sometimes with examples.
In a function description, the name of the function being described appears first. It is followed on the same line by a list of argument names. These names are also used in the body of the description, to stand for the values of the arguments.
The appearance of the keyword &optional in the argument list
indicates that the subsequent arguments may be omitted (omitted
arguments default to nil). Do not write &optional when
you call the function.
The keyword &rest (which must be followed by a single argument
name) indicates that any number of arguments can follow. The single
following argument name will have a value, as a variable, which is a
list of all these remaining arguments. Do not write &rest when
you call the function.
Here is a description of an imaginary function foo:
foo subtracts integer1 from integer2,
then adds all the rest of the arguments to the result. If integer2
is not supplied, then the number 19 is used by default.
(foo 1 5 3 9)
=> 16
(foo 5)
=> 14
More generally,
(foo w x y...) == (+ (- x w) y...)
Any argument whose name contains the name of a type (e.g., integer, integer1 or buffer) is expected to be of that type. A plural of a type (such as buffers) often means a list of objects of that type. Arguments named object may be of any type. (See section Lisp Data Types, for a list of Emacs object types.) Arguments with other sorts of names (e.g., new-file) are discussed specifically in the description of the function. In some sections, features common to the arguments of several functions are described at the beginning.
See section Lambda Expressions, for a more complete description of optional and rest arguments.
Command, macro, and special form descriptions have the same format, but the word `Function' is replaced by `Command', `Macro', or `Special Form', respectively. Commands are simply functions that may be called interactively; macros process their arguments differently from functions (the arguments are not evaluated), but are presented the same way.
Special form descriptions use a more complex notation to specify optional and repeated arguments because they can break the argument list down into separate arguments in more complicated ways. `[optional-arg]' means that optional-arg is optional and `repeated-args...' stands for zero or more arguments. Parentheses are used when several arguments are grouped into additional levels of list structure. Here is an example:
(count-loop (i 0 10) (prin1 i) (princ " ") (prin1 (aref vector i)) (terpri))
If from and to are omitted, var is bound to
nil before the loop begins, and the loop exits if var is
non-nil at the beginning of an iteration. Here is an example:
(count-loop (done)
(if (pending)
(fixit)
(setq done t)))
In this special form, the arguments from and to are optional, but must both be present or both absent. If they are present, inc may optionally be specified as well. These arguments are grouped with the argument var into a list, to distinguish them from body, which includes all remaining elements of the form.
A variable is a name that can hold a value. Although any variable can be set by the user, certain variables that exist specifically so that users can change them are called user options. Ordinary variables and user options are described using a format like that for functions except that there are no arguments.
Here is a description of the imaginary electric-future-map
variable.
User option descriptions have the same format, but `Variable' is replaced by `User Option'.
These facilities provide information about which version of Emacs is in use.
(emacs-version) => "GNU Emacs 20.3.5 (i486-pc-linux-gnulibc1, X toolkit) of Sat Feb 14 1998 on psilocin.gnu.org"
Called interactively, the function prints the same information in the echo area.
current-time (see section Time of Day).
emacs-build-time
=> (13623 62065 344633)
"20.3.1". The last number in this string is not
really part of the Emacs release version number; it is incremented each
time you build Emacs in any given directory.
The following two variables have existed since Emacs version 19.23:
This manual was written by Robert Krawitz, Bil Lewis, Dan LaLiberte, Richard M. Stallman and Chris Welty, the volunteers of the GNU manual group, in an effort extending over several years. Robert J. Chassell helped to review and edit the manual, with the support of the Defense Advanced Research Projects Agency, ARPA Order 6082, arranged by Warren A. Hunt, Jr. of Computational Logic, Inc.
Corrections were supplied by Karl Berry, Jim Blandy, Bard Bloom, Stephane Boucher, David Boyes, Alan Carroll, Richard Davis, Lawrence R. Dodd, Peter Doornbosch, David A. Duff, Chris Eich, Beverly Erlebacher, David Eckelkamp, Ralf Fassel, Eirik Fuller, Stephen Gildea, Bob Glickstein, Eric Hanchrow, George Hartzell, Nathan Hess, Masayuki Ida, Dan Jacobson, Jak Kirman, Bob Knighten, Frederick M. Korz, Joe Lammens, Glenn M. Lewis, K. Richard Magill, Brian Marick, Roland McGrath, Skip Montanaro, John Gardiner Myers, Thomas A. Peterson, Francesco Potorti, Friedrich Pukelsheim, Arnold D. Robbins, Raul Rockwell, Per Starback, Shinichirou Sugou, Kimmo Suominen, Edward Tharp, Bill Trost, Rickard Westman, Jean White, Matthew Wilding, Carl Witty, Dale Worley, Rusty Wright, and David D. Zuhn.
A Lisp object is a piece of data used and manipulated by Lisp programs. For our purposes, a type or data type is a set of possible objects.
Every object belongs to at least one type. Objects of the same type have similar structures and may usually be used in the same contexts. Types can overlap, and objects can belong to two or more types. Consequently, we can ask whether an object belongs to a particular type, but not for "the" type of an object.
A few fundamental object types are built into Emacs. These, from which all other types are constructed, are called primitive types. Each object belongs to one and only one primitive type. These types include integer, float, cons, symbol, string, vector, subr, byte-code function, plus several special types, such as buffer, that are related to editing. (See section Editing Types.)
Each primitive type has a corresponding Lisp function that checks whether an object is a member of that type.
Note that Lisp is unlike many other languages in that Lisp objects are self-typing: the primitive type of the object is implicit in the object itself. For example, if an object is a vector, nothing can treat it as a number; Lisp knows it is a vector, not a number.
In most languages, the programmer must declare the data type of each variable, and the type is known by the compiler but not represented in the data. Such type declarations do not exist in Emacs Lisp. A Lisp variable can have any type of value, and it remembers whatever value you store in it, type and all.
This chapter describes the purpose, printed representation, and read syntax of each of the standard types in GNU Emacs Lisp. Details on how to use these types can be found in later chapters.
The printed representation of an object is the format of the
output generated by the Lisp printer (the function prin1) for
that object. The read syntax of an object is the format of the
input accepted by the Lisp reader (the function read) for that
object. See section Reading and Printing Lisp Objects.
Most objects have more than one possible read syntax. Some types of object have no read syntax, since it may not make sense to enter objects of these types directly in a Lisp program. Except for these cases, the printed representation of an object is also a read syntax for it.
In other languages, an expression is text; it has no other form. In Lisp, an expression is primarily a Lisp object and only secondarily the text that is the object's read syntax. Often there is no need to emphasize this distinction, but you must keep it in the back of your mind, or you will occasionally be very confused.
Every type has a printed representation. Some types have no read
syntax--for example, the buffer type has none. Objects of these types
are printed in hash notation: the characters `#<' followed by
a descriptive string (typically the type name followed by the name of
the object), and closed with a matching `>'. Hash notation cannot
be read at all, so the Lisp reader signals the error
invalid-read-syntax whenever it encounters `#<'.
(current-buffer)
=> #<buffer objects.texi>
When you evaluate an expression interactively, the Lisp interpreter
first reads the textual representation of it, producing a Lisp object,
and then evaluates that object (see section Evaluation). However,
evaluation and reading are separate activities. Reading returns the
Lisp object represented by the text that is read; the object may or may
not be evaluated later. See section Input Functions, for a description of
read, the basic function for reading objects.
A comment is text that is written in a program only for the sake of humans that read the program, and that has no effect on the meaning of the program. In Lisp, a semicolon (`;') starts a comment if it is not within a string or character constant. The comment continues to the end of line. The Lisp reader discards comments; they do not become part of the Lisp objects which represent the program within the Lisp system.
The `#@count' construct, which skips the next count characters, is useful for program-generated comments containing binary data. The Emacs Lisp byte compiler uses this in its output files (see section Byte Compilation). It isn't meant for source files, however.
See section Tips on Writing Comments, for conventions for formatting comments.
There are two general categories of types in Emacs Lisp: those having to do with Lisp programming, and those having to do with editing. The former exist in many Lisp implementations, in one form or another. The latter are unique to Emacs Lisp.
The range of values for integers in Emacs Lisp is -134217728 to
134217727 (28 bits; i.e.,
to
on most machines. (Some machines may provide a wider range.) It is
important to note that the Emacs Lisp arithmetic functions do not check
for overflow. Thus (1+ 134217727) is -134217728 on most
machines.
The read syntax for integers is a sequence of (base ten) digits with an optional sign at the beginning and an optional period at the end. The printed representation produced by the Lisp interpreter never has a leading `+' or a final `.'.
-1 ; The integer -1. 1 ; The integer 1. 1. ; Also The integer 1. +1 ; Also the integer 1. 268435457 ; Also the integer 1 on a 28-bit implementation.
See section Numbers, for more information.
Emacs supports floating point numbers (though there is a compilation option to disable them). The precise range of floating point numbers is machine-specific.
The printed representation for floating point numbers requires either a decimal point (with at least one digit following), an exponent, or both. For example, `1500.0', `15e2', `15.0e2', `1.5e3', and `.15e4' are five ways of writing a floating point number whose value is 1500. They are all equivalent.
See section Numbers, for more information.
A character in Emacs Lisp is nothing more than an integer. In other words, characters are represented by their character codes. For example, the character A is represented as the integer 65.
Individual characters are not often used in programs. It is far more common to work with strings, which are sequences composed of characters. See section String Type.
Characters in strings, buffers, and files are currently limited to the range of 0 to 524287--nineteen bits. But not all values in that range are valid character codes. Codes 0 through 127 are ASCII codes; the rest are non-ASCII (see section Non-ASCII Characters). Characters that represent keyboard input have a much wider range, to encode modifier keys such as Control, Meta and Shift.
Since characters are really integers, the printed representation of a character is a decimal number. This is also a possible read syntax for a character, but writing characters that way in Lisp programs is a very bad idea. You should always use the special read syntax formats that Emacs Lisp provides for characters. These syntax formats start with a question mark.
The usual read syntax for alphanumeric characters is a question mark followed by the character; thus, `?A' for the character A, `?B' for the character B, and `?a' for the character a.
For example:
?Q => 81 ?q => 113
You can use the same syntax for punctuation characters, but it is often a good idea to add a `\' so that the Emacs commands for editing Lisp code don't get confused. For example, `?\ ' is the way to write the space character. If the character is `\', you must use a second `\' to quote it: `?\\'.
You can express the characters Control-g, backspace, tab, newline, vertical tab, formfeed, return, and escape as `?\a', `?\b', `?\t', `?\n', `?\v', `?\f', `?\r', `?\e', respectively. Thus,
?\a => 7 ; C-g ?\b => 8 ; backspace, BS, C-h ?\t => 9 ; tab, TAB, C-i ?\n => 10 ; newline, C-j ?\v => 11 ; vertical tab, C-k ?\f => 12 ; formfeed character, C-l ?\r => 13 ; carriage return, RET, C-m ?\e => 27 ; escape character, ESC, C-[ ?\\ => 92 ; backslash character, \
These sequences which start with backslash are also known as escape sequences, because backslash plays the role of an escape character; this usage has nothing to do with the character ESC.
Control characters may be represented using yet another read syntax. This consists of a question mark followed by a backslash, caret, and the corresponding non-control character, in either upper or lower case. For example, both `?\^I' and `?\^i' are valid read syntax for the character C-i, the character whose value is 9.
Instead of the `^', you can use `C-'; thus, `?\C-i' is equivalent to `?\^I' and to `?\^i':
?\^I => 9 ?\C-I => 9
In strings and buffers, the only control characters allowed are those that exist in ASCII; but for keyboard input purposes, you can turn any character into a control character with `C-'. The character codes for these non-ASCII control characters include the bit as well as the code for the corresponding non-control character. Ordinary terminals have no way of generating non-ASCII control characters, but you can generate them straightforwardly using X and other window systems.
For historical reasons, Emacs treats the DEL character as the control equivalent of ?:
?\^? => 127 ?\C-? => 127
As a result, it is currently not possible to represent the character Control-?, which is a meaningful input character under X, using `\C-'. It is not easy to change this, as various Lisp files refer to DEL in this way.
For representing control characters to be found in files or strings, we recommend the `^' syntax; for control characters in keyboard input, we prefer the `C-' syntax. Which one you use does not affect the meaning of the program, but may guide the understanding of people who read it.
A meta character is a character typed with the META modifier key. The integer that represents such a character has the bit set (which on most machines makes it a negative number). We use high bits for this and other modifiers to make possible a wide range of basic character codes.
In a string, the bit attached to an ASCII character indicates a meta character; thus, the meta characters that can fit in a string have codes in the range from 128 to 255, and are the meta versions of the ordinary ASCII characters. (In Emacs versions 18 and older, this convention was used for characters outside of strings as well.)
The read syntax for meta characters uses `\M-'. For example, `?\M-A' stands for M-A. You can use `\M-' together with octal character codes (see below), with `\C-', or with any other syntax for a character. Thus, you can write M-A as `?\M-A', or as `?\M-\101'. Likewise, you can write C-M-b as `?\M-\C-b', `?\C-\M-b', or `?\M-\002'.
The case of a graphic character is indicated by its character code; for example, ASCII distinguishes between the characters `a' and `A'. But ASCII has no way to represent whether a control character is upper case or lower case. Emacs uses the bit to indicate that the shift key was used in typing a control character. This distinction is possible only when you use X terminals or other special terminals; ordinary terminals do not report the distinction to the computer in any way.
The X Window System defines three other modifier bits that can be set in a character: hyper, super and alt. The syntaxes for these bits are `\H-', `\s-' and `\A-'. (Case is significant in these prefixes.) Thus, `?\H-\M-\A-x' represents Alt-Hyper-Meta-x.
Finally, the most general read syntax for a character represents the
character code in either octal or hex. To use octal, write a question
mark followed by a backslash and the octal character code (up to three
octal digits); thus, `?\101' for the character A,
`?\001' for the character C-a, and ?\002 for the
character C-b. Although this syntax can represent any ASCII
character, it is preferred only when the precise octal value is more
important than the ASCII representation.
?\012 => 10 ?\n => 10 ?\C-j => 10 ?\101 => 65 ?A => 65
To use hex, write a question mark followed by a backslash, `x',
and the hexadecimal character code. You can use any number of hex
digits, so you can represent any character code in this way.
Thus, `?\x41' for the character A, `?\x1' for the
character C-a, and ?\x8e0 for the character
``a'.
A backslash is allowed, and harmless, preceding any character without a special escape meaning; thus, `?\+' is equivalent to `?+'. There is no reason to add a backslash before most characters. However, you should add a backslash before any of the characters `()\|;'`"#.,' to avoid confusing the Emacs commands for editing Lisp code. Also add a backslash before whitespace characters such as space, tab, newline and formfeed. However, it is cleaner to use one of the easily readable escape sequences, such as `\t', instead of an actual whitespace character such as a tab.
A symbol in GNU Emacs Lisp is an object with a name. The symbol name serves as the printed representation of the symbol. In ordinary use, the name is unique--no two symbols have the same name.
A symbol can serve as a variable, as a function name, or to hold a property list. Or it may serve only to be distinct from all other Lisp objects, so that its presence in a data structure may be recognized reliably. In a given context, usually only one of these uses is intended. But you can use one symbol in all of these ways, independently.
A symbol name can contain any characters whatever. Most symbol names are written with letters, digits, and the punctuation characters `-+=*/'. Such names require no special punctuation; the characters of the name suffice as long as the name does not look like a number. (If it does, write a `\' at the beginning of the name to force interpretation as a symbol.) The characters `_~!@$%^&:<>{}' are less often used but also require no special punctuation. Any other characters may be included in a symbol's name by escaping them with a backslash. In contrast to its use in strings, however, a backslash in the name of a symbol simply quotes the single character that follows the backslash. For example, in a string, `\t' represents a tab character; in the name of a symbol, however, `\t' merely quotes the letter `t'. To have a symbol with a tab character in its name, you must actually use a tab (preceded with a backslash). But it's rare to do such a thing.
Common Lisp note: In Common Lisp, lower case letters are always "folded" to upper case, unless they are explicitly escaped. In Emacs Lisp, upper case and lower case letters are distinct.
Here are several examples of symbol names. Note that the `+' in the fifth example is escaped to prevent it from being read as a number. This is not necessary in the sixth example because the rest of the name makes it invalid as a number.
foo ; A symbol named `foo'.
FOO ; A symbol named `FOO', different from `foo'.
char-to-string ; A symbol named `char-to-string'.
1+ ; A symbol named `1+'
; (not `+1', which is an integer).
\+1 ; A symbol named `+1'
; (not a very readable name).
\(*\ 1\ 2\) ; A symbol named `(* 1 2)' (a worse name).
+-*/_~!@$%^&=:<>{} ; A symbol named `+-*/_~!@$%^&=:<>{}'.
; These characters need not be escaped.
A sequence is a Lisp object that represents an ordered set of elements. There are two kinds of sequence in Emacs Lisp, lists and arrays. Thus, an object of type list or of type array is also considered a sequence.
Arrays are further subdivided into strings, vectors, char-tables and
bool-vectors. Vectors can hold elements of any type, but string
elements must be characters, and bool-vector elements must be t
or nil. The characters in a string can have text properties like
characters in a buffer (see section Text Properties); vectors and
bool-vectors do not support text properties even when their elements
happen to be characters. Char-tables are like vectors except that they
are indexed by any valid character code.
Lists, strings and the other array types are different, but they have
important similarities. For example, all have a length l, and all
have elements which can be indexed from zero to l minus one.
Several functions, called sequence functions, accept any kind of
sequence. For example, the function elt can be used to extract
an element of a sequence, given its index. See section Sequences, Arrays, and Vectors.
It is generally impossible to read the same sequence twice, since
sequences are always created anew upon reading. If you read the read
syntax for a sequence twice, you get two sequences with equal contents.
There is one exception: the empty list () always stands for the
same object, nil.
A cons cell is an object that consists of two pointers or slots, called the CAR slot and the CDR slot. Each slot can point to or hold to any Lisp object. We also say that the "the CAR of this cons cell is" whatever object its CAR slot currently points to, and likewise for the CDR.
A list is a series of cons cells, linked together so that the CDR slot of each cons cell holds either the next cons cell or the empty list. See section Lists, for functions that work on lists. Because most cons cells are used as part of lists, the phrase list structure has come to refer to any structure made out of cons cells.
The names CAR and CDR derive from the history of Lisp. The
original Lisp implementation ran on an IBM 704 computer which
divided words into two parts, called the "address" part and the
"decrement"; CAR was an instruction to extract the contents of
the address part of a register, and CDR an instruction to extract
the contents of the decrement. By contrast, "cons cells" are named
for the function cons that creates them, which in turn is named
for its purpose, the construction of cells.
Because cons cells are so central to Lisp, we also have a word for "an object which is not a cons cell". These objects are called atoms.
The read syntax and printed representation for lists are identical, and consist of a left parenthesis, an arbitrary number of elements, and a right parenthesis.
Upon reading, each object inside the parentheses becomes an element
of the list. That is, a cons cell is made for each element. The
CAR slot of the cons cell points to the element, and its CDR
slot points to the next cons cell of the list, which holds the next
element in the list. The CDR slot of the last cons cell is set to
point to nil.
A list can be illustrated by a diagram in which the cons cells are
shown as pairs of boxes, like dominoes. (The Lisp reader cannot read
such an illustration; unlike the textual notation, which can be
understood by both humans and computers, the box illustrations can be
understood only by humans.) This picture represents the three-element
list (rose violet buttercup):
--- --- --- --- --- ---
| | |--> | | |--> | | |--> nil
--- --- --- --- --- ---
| | |
| | |
--> rose --> violet --> buttercup
In this diagram, each box represents a slot that can point to any Lisp object. Each pair of boxes represents a cons cell. Each arrow is a pointer to a Lisp object, either an atom or another cons cell.
In this example, the first box, which holds the CAR of the first
cons cell, points to or "contains" rose (a symbol). The second
box, holding the CDR of the first cons cell, points to the next
pair of boxes, the second cons cell. The CAR of the second cons
cell is violet, and its CDR is the third cons cell. The
CDR of the third (and last) cons cell is nil.
Here is another diagram of the same list, (rose violet
buttercup), sketched in a different manner:
--------------- ---------------- ------------------- | car | cdr | | car | cdr | | car | cdr | | rose | o-------->| violet | o-------->| buttercup | nil | | | | | | | | | | --------------- ---------------- -------------------
A list with no elements in it is the empty list; it is identical
to the symbol nil. In other words, nil is both a symbol
and a list.
Here are examples of lists written in Lisp syntax:
(A 2 "A") ; A list of three elements.
() ; A list of no elements (the empty list).
nil ; A list of no elements (the empty list).
("A ()") ; A list of one element: the string "A ()".
(A ()) ; A list of two elements: A and the empty list.
(A nil) ; Equivalent to the previous.
((A B C)) ; A list of one element
; (which is a list of three elements).
Here is the list (A ()), or equivalently (A nil),
depicted with boxes and arrows:
--- --- --- ---
| | |--> | | |--> nil
--- --- --- ---
| |
| |
--> A --> nil
Dotted pair notation is an alternative syntax for cons cells
that represents the CAR and CDR explicitly. In this syntax,
(a . b) stands for a cons cell whose CAR is
the object a, and whose CDR is the object b. Dotted
pair notation is therefore more general than list syntax. In the dotted
pair notation, the list `(1 2 3)' is written as `(1 . (2 . (3
. nil)))'. For nil-terminated lists, you can use either
notation, but list notation is usually clearer and more convenient.
When printing a list, the dotted pair notation is only used if the
CDR of a cons cell is not a list.
Here's an example using boxes to illustrate dotted pair notation.
This example shows the pair (rose . violet):
--- ---
| | |--> violet
--- ---
|
|
--> rose
You can combine dotted pair notation with list notation to represent
conveniently a chain of cons cells with a non-nil final CDR.
You write a dot after the last element of the list, followed by the
CDR of the final cons cell. For example, (rose violet
. buttercup) is equivalent to (rose . (violet . buttercup)).
The object looks like this:
--- --- --- ---
| | |--> | | |--> buttercup
--- --- --- ---
| |
| |
--> rose --> violet
The syntax (rose . violet . buttercup) is invalid because
there is nothing that it could mean. If anything, it would say to put
buttercup in the CDR of a cons cell whose CDR is already
used for violet.
The list (rose violet) is equivalent to (rose . (violet)),
and looks like this:
--- --- --- ---
| | |--> | | |--> nil
--- --- --- ---
| |
| |
--> rose --> violet
Similarly, the three-element list (rose violet buttercup)
is equivalent to (rose . (violet . (buttercup))).
An association list or alist is a specially-constructed list whose elements are cons cells. In each element, the CAR is considered a key, and the CDR is considered an associated value. (In some cases, the associated value is stored in the CAR of the CDR.) Association lists are often used as stacks, since it is easy to add or remove associations at the front of the list.
For example,
(setq alist-of-colors
'((rose . red) (lily . white) (buttercup . yellow)))
sets the variable alist-of-colors to an alist of three elements. In the
first element, rose is the key and red is the value.
See section Association Lists, for a further explanation of alists and for functions that work on alists.
An array is composed of an arbitrary number of slots for pointing to other Lisp objects, arranged in a contiguous block of memory. Accessing any element of an array takes approximately the same amount of time. In contrast, accessing an element of a list requires time proportional to the position of the element in the list. (Elements at the end of a list take longer to access than elements at the beginning of a list.)
Emacs defines four types of array: strings, vectors, bool-vectors, and char-tables.
A string is an array of characters and a vector is an array of
arbitrary objects. A bool-vector can hold only t or nil.
These kinds of array may have any length up to the largest integer.
Char-tables are sparse arrays indexed by any valid character code; they
can hold arbitrary objects.
The first element of an array has index zero, the second element has index 1, and so on. This is called zero-origin indexing. For example, an array of four elements has indices 0, 1, 2, and 3. The largest possible index value is one less than the length of the array. Once an array is created, its length is fixed.
All Emacs Lisp arrays are one-dimensional. (Most other programming languages support multidimensional arrays, but they are not essential; you can get the same effect with an array of arrays.) Each type of array has its own read syntax; see the following sections for details.
The array type is contained in the sequence type and contains the string type, the vector type, the bool-vector type, and the char-table type.
A string is an array of characters. Strings are used for many purposes in Emacs, as can be expected in a text editor; for example, as the names of Lisp symbols, as messages for the user, and to represent text extracted from buffers. Strings in Lisp are constants: evaluation of a string returns the same string.
See section Strings and Characters, for functions that operate on strings.
The read syntax for strings is a double-quote, an arbitrary number of
characters, and another double-quote, "like this". To include a
double-quote in a string, precede it with a backslash; thus, "\""
is a string containing just a single double-quote character. Likewise,
you can include a backslash by preceding it with another backslash, like
this: "this \\ is a single embedded backslash".
The newline character is not special in the read syntax for strings; if you write a new line between the double-quotes, it becomes a character in the string. But an escaped newline--one that is preceded by `\'---does not become part of the string; i.e., the Lisp reader ignores an escaped newline while reading a string. An escaped space `\ ' is likewise ignored.
"It is useful to include newlines
in documentation strings,
but the newline is \
ignored if escaped."
=> "It is useful to include newlines
in documentation strings,
but the newline is ignored if escaped."
You can include a non-ASCII international character in a string constant by writing it literally. There are two text representations for non-ASCII characters in Emacs strings (and in buffers): unibyte and multibyte. If the string constant is read from a multibyte source, such as a multibyte buffer or string, or a file that would be visited as multibyte, then the character is read as a multibyte character, and that makes the string multibyte. If the string constant is read from a unibyte source, then the character is read as unibyte and that makes the string unibyte.
You can also represent a multibyte non-ASCII character with its character code, using a hex escape, `\xnnnnnnn', with as many digits as necessary. (Multibyte non-ASCII character codes are all greater than 256.) Any character which is not a valid hex digit terminates this construct. If the character that would follow is a hex digit, write `\ ' (backslash and space) to terminate the hex escape--for example, `\x8e0\ ' represents one character, `a' with grave accent. `\ ' in a string constant is just like backslash-newline; it does not contribute any character to the string, but it does terminate the preceding hex escape.
Using a multibyte hex escape forces the string to multibyte. You can represent a unibyte non-ASCII character with its character code, which must be in the range from 128 (0200 octal) to 255 (0377 octal). This forces a unibyte string. See section Text Representations, for more information about the two text representations.
You can use the same backslash escape-sequences in a string constant
as in character literals (but do not use the question mark that begins a
character constant). For example, you can write a string containing the
nonprinting characters tab and C-a, with commas and spaces between
them, like this: "\t, \C-a". See section Character Type, for a
description of the read syntax for characters.
However, not all of the characters you can write with backslash escape-sequences are valid in strings. The only control characters that a string can hold are the ASCII control characters. Strings do not distinguish case in ASCII control characters.
Properly speaking, strings cannot hold meta characters; but when a
string is to be used as a key sequence, there is a special convention
that provides a way to represent meta versions of ASCII characters in a
string. If you use the `\M-' syntax to indicate a meta character
in a string constant, this sets the
bit of the character in the string. If the string is used in
define-key or lookup-key, this numeric code is translated
into the equivalent meta character. See section Character Type.
Strings cannot hold characters that have the hyper, super, or alt modifiers.
A string can hold properties for the characters it contains, in addition to the characters themselves. This enables programs that copy text between strings and buffers to copy the text's properties with no special effort. See section Text Properties, for an explanation of what text properties mean. Strings with text properties use a special read and print syntax:
#("characters" property-data...)
where property-data consists of zero or more elements, in groups of three as follows:
beg end plist
The elements beg and end are integers, and together specify a range of indices in the string; plist is the property list for that range. For example,
#("foo bar" 0 3 (face bold) 3 4 nil 4 7 (face italic))
represents a string whose textual contents are `foo bar', in which
the first three characters have a face property with value
bold, and the last three have a face property with value
italic. (The fourth character has no text properties, so its
property list is nil. It is not actually necessary to mention
ranges with nil as the property list, since any characters not
mentioned in any range will default to having no properties.)
A vector is a one-dimensional array of elements of any type. It takes a constant amount of time to access any element of a vector. (In a list, the access time of an element is proportional to the distance of the element from the beginning of the list.)
The printed representation of a vector consists of a left square bracket, the elements, and a right square bracket. This is also the read syntax. Like numbers and strings, vectors are considered constants for evaluation.
[1 "two" (three)] ; A vector of three elements.
=> [1 "two" (three)]
See section Vectors, for functions that work with vectors.
A char-table is a one-dimensional array of elements of any type, indexed by character codes. Char-tables have certain extra features to make them more useful for many jobs that involve assigning information to character codes--for example, a char-table can have a parent to inherit from, a default value, and a small number of extra slots to use for special purposes. A char-table can also specify a single value for a whole character set.
The printed representation of a char-table is like a vector except that there is an extra `#^' at the beginning.
See section Char-Tables, for special functions to operate on char-tables. Uses of char-tables include:
A bool-vector is a one-dimensional array of elements that
must be t or nil.
The printed representation of a Bool-vector is like a string, except
that it begins with `#&' followed by the length. The string
constant that follows actually specifies the contents of the bool-vector
as a bitmap--each "character" in the string contains 8 bits, which
specify the next 8 elements of the bool-vector (1 stands for t,
and 0 for nil). The least significant bits of the character
correspond to the lowest indices in the bool-vector. If the length is not a
multiple of 8, the printed representation shows extra elements, but
these extras really make no difference.
(make-bool-vector 3 t)
=> #&3"\007"
(make-bool-vector 3 nil)
=> #&3"\0"
;; These are equal since only the first 3 bits are used.
(equal #&3"\377" #&3"\007")
=> t
Just as functions in other programming languages are executable,
Lisp function objects are pieces of executable code. However,
functions in Lisp are primarily Lisp objects, and only secondarily the
text which represents them. These Lisp objects are lambda expressions:
lists whose first element is the symbol lambda (see section Lambda Expressions).
In most programming languages, it is impossible to have a function without a name. In Lisp, a function has no intrinsic name. A lambda expression is also called an anonymous function (see section Anonymous Functions). A named function in Lisp is actually a symbol with a valid function in its function cell (see section Defining Functions).
Most of the time, functions are called when their names are written in
Lisp expressions in Lisp programs. However, you can construct or obtain
a function object at run time and then call it with the primitive
functions funcall and apply. See section Calling Functions.
A Lisp macro is a user-defined construct that extends the Lisp
language. It is represented as an object much like a function, but with
different argument-passing semantics. A Lisp macro has the form of a
list whose first element is the symbol macro and whose CDR
is a Lisp function object, including the lambda symbol.
Lisp macro objects are usually defined with the built-in
defmacro function, but any list that begins with macro is
a macro as far as Emacs is concerned. See section Macros, for an explanation
of how to write a macro.
Warning: Lisp macros and keyboard macros (see section Keyboard Macros) are entirely different things. When we use the word "macro" without qualification, we mean a Lisp macro, not a keyboard macro.
A primitive function is a function callable from Lisp but written in the C programming language. Primitive functions are also called subrs or built-in functions. (The word "subr" is derived from "subroutine".) Most primitive functions evaluate all their arguments when they are called. A primitive function that does not evaluate all its arguments is called a special form (see section Special Forms).
It does not matter to the caller of a function whether the function is primitive. However, this does matter if you try to redefine a primitive with a function written in Lisp. The reason is that the primitive function may be called directly from C code. Calls to the redefined function from Lisp will use the new definition, but calls from C code may still use the built-in definition. Therefore, we discourage redefinition of primitive functions.
The term function refers to all Emacs functions, whether written in Lisp or C. See section Function Type, for information about the functions written in Lisp.
Primitive functions have no read syntax and print in hash notation with the name of the subroutine.
(symbol-function 'car) ; Access the function cell
; of the symbol.
=> #<subr car>
(subrp (symbol-function 'car)) ; Is this a primitive function?
=> t ; Yes.
The byte compiler produces byte-code function objects. Internally, a byte-code function object is much like a vector; however, the evaluator handles this data type specially when it appears as a function to be called. See section Byte Compilation, for information about the byte compiler.
The printed representation and read syntax for a byte-code function object is like that for a vector, with an additional `#' before the opening `['.
An autoload object is a list whose first element is the symbol
autoload. It is stored as the function definition of a symbol as
a placeholder for the real definition; it says that the real definition
is found in a file of Lisp code that should be loaded when necessary.
The autoload object contains the name of the file, plus some other
information about the real definition.
After the file has been loaded, the symbol should have a new function definition that is not an autoload object. The new definition is then called as if it had been there to begin with. From the user's point of view, the function call works as expected, using the function definition in the loaded file.
An autoload object is usually created with the function
autoload, which stores the object in the function cell of a
symbol. See section Autoload, for more details.
The types in the previous section are used for general programming purposes, and most of them are common to most Lisp dialects. Emacs Lisp provides several additional data types for purposes connected with editing.
A buffer is an object that holds text that can be edited (see section Buffers). Most buffers hold the contents of a disk file (see section Files) so they can be edited, but some are used for other purposes. Most buffers are also meant to be seen by the user, and therefore displayed, at some time, in a window (see section Windows). But a buffer need not be displayed in any window.
The contents of a buffer are much like a string, but buffers are not used like strings in Emacs Lisp, and the available operations are different. For example, you can insert text efficiently into an existing buffer, whereas "inserting" text into a string requires concatenating substrings, and the result is an entirely new string object.
Each buffer has a designated position called point (see section Positions). At any time, one buffer is the current buffer. Most editing commands act on the contents of the current buffer in the neighborhood of point. Many of the standard Emacs functions manipulate or test the characters in the current buffer; a whole chapter in this manual is devoted to describing these functions (see section Text).
Several other data structures are associated with each buffer:
The local keymap and variable list contain entries that individually override global bindings or values. These are used to customize the behavior of programs in different buffers, without actually changing the programs.
A buffer may be indirect, which means it shares the text of another buffer, but presents it differently. See section Indirect Buffers.
Buffers have no read syntax. They print in hash notation, showing the buffer name.
(current-buffer)
=> #<buffer objects.texi>
A marker denotes a position in a specific buffer. Markers therefore have two components: one for the buffer, and one for the position. Changes in the buffer's text automatically relocate the position value as necessary to ensure that the marker always points between the same two characters in the buffer.
Markers have no read syntax. They print in hash notation, giving the current character position and the name of the buffer.
(point-marker)
=> #<marker at 10779 in objects.texi>
See section Markers, for information on how to test, create, copy, and move markers.
A window describes the portion of the terminal screen that Emacs uses to display a buffer. Every window has one associated buffer, whose contents appear in the window. By contrast, a given buffer may appear in one window, no window, or several windows.
Though many windows may exist simultaneously, at any time one window is designated the selected window. This is the window where the cursor is (usually) displayed when Emacs is ready for a command. The selected window usually displays the current buffer, but this is not necessarily the case.
Windows are grouped on the screen into frames; each window belongs to one and only one frame. See section Frame Type.
Windows have no read syntax. They print in hash notation, giving the window number and the name of the buffer being displayed. The window numbers exist to identify windows uniquely, since the buffer displayed in any given window can change frequently.
(selected-window)
=> #<window 1 on objects.texi>
See section Windows, for a description of the functions that work on windows.
A frame is a rectangle on the screen that contains one or more Emacs windows. A frame initially contains a single main window (plus perhaps a minibuffer window) which you can subdivide vertically or horizontally into smaller windows.
Frames have no read syntax. They print in hash notation, giving the frame's title, plus its address in core (useful to identify the frame uniquely).
(selected-frame)
=> #<frame emacs@psilocin.gnu.org 0xdac80>
See section Frames, for a description of the functions that work on frames.
A window configuration stores information about the positions, sizes, and contents of the windows in a frame, so you can recreate the same arrangement of windows later.
Window configurations do not have a read syntax; their print syntax looks like `#<window-configuration>'. See section Window Configurations, for a description of several functions related to window configurations.
A frame configuration stores information about the positions,
sizes, and contents of the windows in all frames. It is actually
a list whose CAR is frame-configuration and whose
CDR is an alist. Each alist element describes one frame,
which appears as the CAR of that element.
See section Frame Configurations, for a description of several functions related to frame configurations.
The word process usually means a running program. Emacs itself runs in a process of this sort. However, in Emacs Lisp, a process is a Lisp object that designates a subprocess created by the Emacs process. Programs such as shells, GDB, ftp, and compilers, running in subprocesses of Emacs, extend the capabilities of Emacs.
An Emacs subprocess takes textual input from Emacs and returns textual output to Emacs for further manipulation. Emacs can also send signals to the subprocess.
Process objects have no read syntax. They print in hash notation, giving the name of the process:
(process-list)
=> (#<process shell>)
See section Processes, for information about functions that create, delete, return information about, send input or signals to, and receive output from processes.
A stream is an object that can be used as a source or sink for characters--either to supply characters for input or to accept them as output. Many different types can be used this way: markers, buffers, strings, and functions. Most often, input streams (character sources) obtain characters from the keyboard, a buffer, or a file, and output streams (character sinks) send characters to a buffer, such as a `*Help*' buffer, or to the echo area.
The object nil, in addition to its other meanings, may be used
as a stream. It stands for the value of the variable
standard-input or standard-output. Also, the object
t as a stream specifies input using the minibuffer
(see section Minibuffers) or output in the echo area (see section The Echo Area).
Streams have no special printed representation or read syntax, and print as whatever primitive type they are.
See section Reading and Printing Lisp Objects, for a description of functions related to streams, including parsing and printing functions.
A keymap maps keys typed by the user to commands. This mapping
controls how the user's command input is executed. A keymap is actually
a list whose CAR is the symbol keymap.
See section Keymaps, for information about creating keymaps, handling prefix keys, local as well as global keymaps, and changing key bindings.
An overlay specifies properties that apply to a part of a buffer. Each overlay applies to a specified range of the buffer, and contains a property list (a list whose elements are alternating property names and values). Overlay properties are used to present parts of the buffer temporarily in a different display style. Overlays have no read syntax, and print in hash notation, giving the buffer name and range of positions.
See section Overlays, for how to create and use overlays.
The Emacs Lisp interpreter itself does not perform type checking on the actual arguments passed to functions when they are called. It could not do so, since function arguments in Lisp do not have declared data types, as they do in other programming languages. It is therefore up to the individual function to test whether each actual argument belongs to a type that the function can use.
All built-in functions do check the types of their actual arguments
when appropriate, and signal a wrong-type-argument error if an
argument is of the wrong type. For example, here is what happens if you
pass an argument to + that it cannot handle:
(+ 2 'a)
error--> Wrong type argument: number-or-marker-p, a
If you want your program to handle different types differently, you must do explicit type checking. The most common way to check the type of an object is to call a type predicate function. Emacs has a type predicate for each type, as well as some predicates for combinations of types.
A type predicate function takes one argument; it returns t if
the argument belongs to the appropriate type, and nil otherwise.
Following a general Lisp convention for predicate functions, most type
predicates' names end with `p'.
Here is an example which uses the predicates listp to check for
a list and symbolp to check for a symbol.
(defun add-on (x)
(cond ((symbolp x)
;; If X is a symbol, put it on LIST.
(setq list (cons x list)))
((listp x)
;; If X is a list, add its elements to LIST.
(setq list (append x list)))
(t
;; We handle only symbols and lists.
(error "Invalid argument %s in add-on" x))))
Here is a table of predefined type predicates, in alphabetical order, with references to further information.
atom
arrayp
bool-vector-p
bufferp
byte-code-function-p
case-table-p
char-or-string-p
char-table-p
commandp
consp
display-table-p
floatp
frame-configuration-p
frame-live-p
framep
functionp
integer-or-marker-p
integerp
keymapp
listp
markerp
wholenump
nlistp
numberp
number-or-marker-p
overlayp
processp
sequencep
stringp
subrp
symbolp
syntax-table-p
user-variable-p
vectorp
window-configuration-p
window-live-p
windowp
The most general way to check the type of an object is to call the
function type-of. Recall that each object belongs to one and
only one primitive type; type-of tells you which one (see section Lisp Data Types). But type-of knows nothing about non-primitive
types. In most cases, it is more convenient to use type predicates than
type-of.
symbol,
integer, float, string, cons, vector,
char-table, bool-vector, subr,
compiled-function, marker, overlay, window,
buffer, frame, process, or
window-configuration.
(type-of 1)
=> integer
(type-of 'nil)
=> symbol
(type-of '()) ; () is nil.
=> symbol
(type-of '(x))
=> cons
Here we describe two functions that test for equality between any two objects. Other functions test equality between objects of specific types, e.g., strings. For these predicates, see the appropriate chapter describing the data type.
t if object1 and object2 are
the same object, nil otherwise. The "same object" means that a
change in one will be reflected by the same change in the other.
eq returns t if object1 and object2 are
integers with the same value. Also, since symbol names are normally
unique, if the arguments are symbols with the same name, they are
eq. For other types (e.g., lists, vectors, strings), two
arguments with the same contents or elements are not necessarily
eq to each other: they are eq only if they are the same
object.
(eq 'foo 'foo)
=> t
(eq 456 456)
=> t
(eq "asdf" "asdf")
=> nil
(eq '(1 (2 (3))) '(1 (2 (3))))
=> nil
(setq foo '(1 (2 (3))))
=> (1 (2 (3)))
(eq foo foo)
=> t
(eq foo '(1 (2 (3))))
=> nil
(eq [(1 2) 3] [(1 2) 3])
=> nil
(eq (point-marker) (point-marker))
=> nil
The make-symbol function returns an uninterned symbol, distinct
from the symbol that is used if you write the name in a Lisp expression.
Distinct symbols with the same name are not eq. See section Creating and Interning Symbols.
(eq (make-symbol "foo") 'foo)
=> nil
t if object1 and object2 have
equal components, nil otherwise. Whereas eq tests if its
arguments are the same object, equal looks inside nonidentical
arguments to see if their elements are the same. So, if two objects are
eq, they are equal, but the converse is not always true.
(equal 'foo 'foo)
=> t
(equal 456 456)
=> t
(equal "asdf" "asdf")
=> t
(eq "asdf" "asdf")
=> nil
(equal '(1 (2 (3))) '(1 (2 (3))))
=> t
(eq '(1 (2 (3))) '(1 (2 (3))))
=> nil
(equal [(1 2) 3] [(1 2) 3])
=> t
(eq [(1 2) 3] [(1 2) 3])
=> nil
(equal (point-marker) (point-marker))
=> t
(eq (point-marker) (point-marker))
=> nil
Comparison of strings is case-sensitive, but does not take account of text properties--it compares only the characters in the strings. A unibyte string never equals a multibyte string unless the contents are entirely ASCII (see section Text Representations).
(equal "asdf" "ASDF")
=> nil
Two distinct buffers are never equal, even if their contents
are the same.
The test for equality is implemented recursively, and circular lists may therefore cause infinite recursion (leading to an error).
GNU Emacs supports two numeric data types: integers and floating point numbers. Integers are whole numbers such as -3, 0, 7, 13, and 511. Their values are exact. Floating point numbers are numbers with fractional parts, such as -4.5, 0.0, or 2.71828. They can also be expressed in exponential notation: 1.5e2 equals 150; in this example, `e2' stands for ten to the second power, and that is multiplied by 1.5. Floating point values are not exact; they have a fixed, limited amount of precision.
The range of values for an integer depends on the machine. The minimum range is -134217728 to 134217727 (28 bits; i.e., to but some machines may provide a wider range. Many examples in this chapter assume an integer has 28 bits.
The Lisp reader reads an integer as a sequence of digits with optional initial sign and optional final period.
1 ; The integer 1. 1. ; The integer 1. +1 ; Also the integer 1. -1 ; The integer -1. 268435457 ; Also the integer 1, due to overflow. 0 ; The integer 0. -0 ; The integer 0.
To understand how various functions work on integers, especially the bitwise operators (see section Bitwise Operations on Integers), it is often helpful to view the numbers in their binary form.
In 28-bit binary, the decimal integer 5 looks like this:
0000 0000 0000 0000 0000 0000 0101
(We have inserted spaces between groups of 4 bits, and two spaces between groups of 8 bits, to make the binary integer easier to read.)
The integer -1 looks like this:
1111 1111 1111 1111 1111 1111 1111
-1 is represented as 28 ones. (This is called two's complement notation.)
The negative integer, -5, is creating by subtracting 4 from -1. In binary, the decimal integer 4 is 100. Consequently, -5 looks like this:
1111 1111 1111 1111 1111 1111 1011
In this implementation, the largest 28-bit binary integer value is 134,217,727 in decimal. In binary, it looks like this:
0111 1111 1111 1111 1111 1111 1111
Since the arithmetic functions do not check whether integers go outside their range, when you add 1 to 134,217,727, the value is the negative integer -134,217,728:
(+ 1 134217727)
=> -134217728
=> 1000 0000 0000 0000 0000 0000 0000
Many of the functions described in this chapter accept markers for arguments in place of numbers. (See section Markers.) Since the actual arguments to such functions may be either numbers or markers, we often give these arguments the name number-or-marker. When the argument value is a marker, its position value is used and its buffer is ignored.
Floating point numbers are useful for representing numbers that are
not integral. The precise range of floating point numbers is
machine-specific; it is the same as the range of the C data type
double on the machine you are using.
The read-syntax for floating point numbers requires either a decimal point (with at least one digit following), an exponent, or both. For example, `1500.0', `15e2', `15.0e2', `1.5e3', and `.15e4' are five ways of writing a floating point number whose value is 1500. They are all equivalent. You can also use a minus sign to write negative floating point numbers, as in `-1.0'.
Most modern computers support the IEEE floating point standard, which
provides for positive infinity and negative infinity as floating point
values. It also provides for a class of values called NaN or
"not-a-number"; numerical functions return such values in cases where
there is no correct answer. For example, (sqrt -1.0) returns a
NaN. For practical purposes, there's no significant difference between
different NaN values in Emacs Lisp, and there's no rule for precisely
which NaN value should be used in a particular case, so Emacs Lisp
doesn't try to distinguish them. Here are the read syntaxes for
these special floating point values:
In addition, the value -0.0 is distinguishable from ordinary
zero in IEEE floating point (although equal and = consider
them equal values).
You can use logb to extract the binary exponent of a floating
point number (or estimate the logarithm of an integer):
(logb 10)
=> 3
(logb 10.0e20)
=> 69
The functions in this section test whether the argument is a number or
whether it is a certain sort of number. The functions integerp
and floatp can take any type of Lisp object as argument (the
predicates would not be of much use otherwise); but the zerop
predicate requires a number as its argument. See also
integer-or-marker-p and number-or-marker-p, in
section Predicates on Markers.
t if so, nil otherwise.
floatp does not exist in Emacs versions 18 and earlier.
t if so, nil otherwise.
t if so, nil otherwise.
wholenump predicate (whose name comes from the phrase
"whole-number-p") tests to see whether its argument is a nonnegative
integer, and returns t if so, nil otherwise. 0 is
considered non-negative.
t
if so, nil otherwise. The argument must be a number.
These two forms are equivalent: (zerop x) == (= x 0).
To test numbers for numerical equality, you should normally use
=, not eq. There can be many distinct floating point
number objects with the same numeric value. If you use eq to
compare them, then you test whether two values are the same
object. By contrast, = compares only the numeric values
of the objects.
At present, each integer value has a unique Lisp object in Emacs Lisp.
Therefore, eq is equivalent to = where integers are
concerned. It is sometimes convenient to use eq for comparing an
unknown value with an integer, because eq does not report an
error if the unknown value is not a number--it accepts arguments of any
type. By contrast, = signals an error if the arguments are not
numbers or markers. However, it is a good idea to use = if you
can, even for comparing integers, just in case we change the
representation of integers in a future Emacs version.
Sometimes it is useful to compare numbers with equal; it treats
two numbers as equal if they have the same data type (both integers, or
both floating point) and the same value. By contrast, = can
treat an integer and a floating point number as equal.
There is another wrinkle: because floating point arithmetic is not exact, it is often a bad idea to check for equality of two floating point values. Usually it is better to test for approximate equality. Here's a function to do this:
(defvar fuzz-factor 1.0e-6)
(defun approx-equal (x y)
(or (and (= x 0) (= y 0))
(< (/ (abs (- x y))
(max (abs x) (abs y)))
fuzz-factor)))
Common Lisp note: Comparing numbers in Common Lisp always requires
=because Common Lisp implements multi-word integers, and two distinct integer objects can have the same numeric value. Emacs Lisp can have just one integer object for any given value because it has a limited range of integer values.
t if so, nil otherwise.
t if they are not, and nil if they are.
t if so, nil otherwise.
t if so, nil
otherwise.
t if so, nil
otherwise.
t if so, nil
otherwise.
(max 20)
=> 20
(max 1 2.5)
=> 2.5
(max 1 3 2.5)
=> 3
(min -4 1)
=> -4
To convert an integer to floating point, use the function float.
float returns
it unchanged.
There are four functions to convert floating point numbers to integers; they differ in how they round. These functions accept integer arguments also, and return such arguments unchanged.
If divisor is specified, number is divided by divisor
before the floor is taken; this uses the kind of division operation that
corresponds to mod, rounding downward. An arith-error
results if divisor is 0.
Emacs Lisp provides the traditional four arithmetic operations: addition, subtraction, multiplication, and division. Remainder and modulus functions supplement the division functions. The functions to add or subtract 1 are provided because they are traditional in Lisp and commonly used.
All of these functions except % return a floating point value
if any argument is floating.
It is important to note that in Emacs Lisp, arithmetic functions
do not check for overflow. Thus (1+ 134217727) may evaluate to
-134217728, depending on your hardware.
(setq foo 4)
=> 4
(1+ foo)
=> 5
This function is not analogous to the C operator ++---it does not
increment a variable. It just computes a sum. Thus, if we continue,
foo
=> 4
If you want to increment the variable, you must use setq,
like this:
(setq foo (1+ foo))
=> 5
+ returns 0.
(+)
=> 0
(+ 1)
=> 1
(+ 1 2 3 4)
=> 10
- function serves two purposes: negation and subtraction.
When - has a single argument, the value is the negative of the
argument. When there are multiple arguments, - subtracts each of
the more-numbers-or-markers from number-or-marker,
cumulatively. If there are no arguments, the result is 0.
(- 10 1 2 3 4)
=> 0
(- 10)
=> -10
(-)
=> 0
* returns 1.
(*)
=> 1
(* 1)
=> 1
(* 1 2 3 4)
=> 24
If all the arguments are integers, then the result is an integer too.
This means the result has to be rounded. On most machines, the result
is rounded towards zero after each division, but some machines may round
differently with negative arguments. This is because the Lisp function
/ is implemented using the C division operator, which also
permits machine-dependent rounding. As a practical matter, all known
machines round in the standard fashion.
If you divide an integer by 0, an arith-error error is signaled.
(See section Errors.) Floating point division by zero returns either
infinity or a NaN if your machine supports IEEE floating point;
otherwise, it signals an arith-error error.
(/ 6 2)
=> 3
(/ 5 2)
=> 2
(/ 5.0 2)
=> 2.5
(/ 5 2.0)
=> 2.5
(/ 5.0 2.0)
=> 2.5
(/ 25 3 2)
=> 4
(/ -17 6)
=> -2
The result of (/ -17 6) could in principle be -3 on some
machines.
For negative arguments, the remainder is in principle machine-dependent since the quotient is; but in practice, all known machines behave alike.
An arith-error results if divisor is 0.
(% 9 4)
=> 1
(% -9 4)
=> -1
(% 9 -4)
=> 1
(% -9 -4)
=> -1
For any two integers dividend and divisor,
(+ (% dividend divisor) (* (/ dividend divisor) divisor))
always equals dividend.
Unlike %, mod returns a well-defined result for negative
arguments. It also permits floating point arguments; it rounds the
quotient downward (towards minus infinity) to an integer, and uses that
quotient to compute the remainder.
An arith-error results if divisor is 0.
(mod 9 4)
=> 1
(mod -9 4)
=> 3
(mod 9 -4)
=> -3
(mod -9 -4)
=> -1
(mod 5.5 2.5)
=> .5
For any two numbers dividend and divisor,
(+ (mod dividend divisor) (* (floor dividend divisor) divisor))
always equals dividend, subject to rounding error if either
argument is floating point. For floor, see section Numeric Conversions.
The functions ffloor, fceiling, fround, and
ftruncate take a floating point argument and return a floating
point result whose value is a nearby integer. ffloor returns the
nearest integer below; fceiling, the nearest integer above;
ftruncate, the nearest integer in the direction towards zero;
fround, the nearest integer.
In a computer, an integer is represented as a binary number, a sequence of bits (digits which are either zero or one). A bitwise operation acts on the individual bits of such a sequence. For example, shifting moves the whole sequence left or right one or more places, reproducing the same pattern "moved over".
The bitwise operations in Emacs Lisp apply only to integers.
lsh, which is an abbreviation for logical shift, shifts the
bits in integer1 to the left count places, or to the right
if count is negative, bringing zeros into the vacated bits. If
count is negative, lsh shifts zeros into the leftmost
(most-significant) bit, producing a positive result even if
integer1 is negative. Contrast this with ash, below.
Here are two examples of lsh, shifting a pattern of bits one
place to the left. We show only the low-order eight bits of the binary
pattern; the rest are all zero.
(lsh 5 1)
=> 10
;; Decimal 5 becomes decimal 10.
00000101 => 00001010
(lsh 7 1)
=> 14
;; Decimal 7 becomes decimal 14.
00000111 => 00001110
As the examples illustrate, shifting the pattern of bits one place to the left produces a number that is twice the value of the previous number.
Shifting a pattern of bits two places to the left produces results like this (with 8-bit binary numbers):
(lsh 3 2)
=> 12
;; Decimal 3 becomes decimal 12.
00000011 => 00001100
On the other hand, shifting one place to the right looks like this:
(lsh 6 -1)
=> 3
;; Decimal 6 becomes decimal 3.
00000110 => 00000011
(lsh 5 -1)
=> 2
;; Decimal 5 becomes decimal 2.
00000101 => 00000010
As the example illustrates, shifting one place to the right divides the value of a positive integer by two, rounding downward.
The function lsh, like all Emacs Lisp arithmetic functions, does
not check for overflow, so shifting left can discard significant bits
and change the sign of the number. For example, left shifting
134,217,727 produces -2 on a 28-bit machine:
(lsh 134217727 1) ; left shift
=> -2
In binary, in the 28-bit implementation, the argument looks like this:
;; Decimal 134,217,727 0111 1111 1111 1111 1111 1111 1111
which becomes the following when left shifted:
;; Decimal -2 1111 1111 1111 1111 1111 1111 1110
ash (arithmetic shift) shifts the bits in integer1
to the left count places, or to the right if count
is negative.
ash gives the same results as lsh except when
integer1 and count are both negative. In that case,
ash puts ones in the empty bit positions on the left, while
lsh puts zeros in those bit positions.
Thus, with ash, shifting the pattern of bits one place to the right
looks like this:
(ash -6 -1) => -3
;; Decimal -6 becomes decimal -3.
1111 1111 1111 1111 1111 1111 1010
=>
1111 1111 1111 1111 1111 1111 1101
In contrast, shifting the pattern of bits one place to the right with
lsh looks like this:
(lsh -6 -1) => 134217725
;; Decimal -6 becomes decimal 134,217,725.
1111 1111 1111 1111 1111 1111 1010
=>
0111 1111 1111 1111 1111 1111 1101
Here are other examples:
; 28-bit binary values
(lsh 5 2) ; 5 = 0000 0000 0000 0000 0000 0000 0101
=> 20 ; = 0000 0000 0000 0000 0000 0001 0100
(ash 5 2)
=> 20
(lsh -5 2) ; -5 = 1111 1111 1111 1111 1111 1111 1011
=> -20 ; = 1111 1111 1111 1111 1111 1110 1100
(ash -5 2)
=> -20
(lsh 5 -2) ; 5 = 0000 0000 0000 0000 0000 0000 0101
=> 1 ; = 0000 0000 0000 0000 0000 0000 0001
(ash 5 -2)
=> 1
(lsh -5 -2) ; -5 = 1111 1111 1111 1111 1111 1111 1011
=> 4194302 ; = 0011 1111 1111 1111 1111 1111 1110
(ash -5 -2) ; -5 = 1111 1111 1111 1111 1111 1111 1011
=> -2 ; = 1111 1111 1111 1111 1111 1111 1110
For example, using 4-bit binary numbers, the "logical and" of 13 and 12 is 12: 1101 combined with 1100 produces 1100. In both the binary numbers, the leftmost two bits are set (i.e., they are 1's), so the leftmost two bits of the returned value are set. However, for the rightmost two bits, each is zero in at least one of the arguments, so the rightmost two bits of the returned value are 0's.
Therefore,
(logand 13 12)
=> 12
If logand is not passed any argument, it returns a value of
-1. This number is an identity element for logand
because its binary representation consists entirely of ones. If
logand is passed just one argument, it returns that argument.
; 28-bit binary values
(logand 14 13) ; 14 = 0000 0000 0000 0000 0000 0000 1110
; 13 = 0000 0000 0000 0000 0000 0000 1101
=> 12 ; 12 = 0000 0000 0000 0000 0000 0000 1100
(logand 14 13 4) ; 14 = 0000 0000 0000 0000 0000 0000 1110
; 13 = 0000 0000 0000 0000 0000 0000 1101
; 4 = 0000 0000 0000 0000 0000 0000 0100
=> 4 ; 4 = 0000 0000 0000 0000 0000 0000 0100
(logand)
=> -1 ; -1 = 1111 1111 1111 1111 1111 1111 1111
logior is
passed just one argument, it returns that argument.
; 28-bit binary values
(logior 12 5) ; 12 = 0000 0000 0000 0000 0000 0000 1100
; 5 = 0000 0000 0000 0000 0000 0000 0101
=> 13 ; 13 = 0000 0000 0000 0000 0000 0000 1101
(logior 12 5 7) ; 12 = 0000 0000 0000 0000 0000 0000 1100
; 5 = 0000 0000 0000 0000 0000 0000 0101
; 7 = 0000 0000 0000 0000 0000 0000 0111
=> 15 ; 15 = 0000 0000 0000 0000 0000 0000 1111
logxor is passed just one argument, it returns that argument.
; 28-bit binary values
(logxor 12 5) ; 12 = 0000 0000 0000 0000 0000 0000 1100
; 5 = 0000 0000 0000 0000 0000 0000 0101
=> 9 ; 9 = 0000 0000 0000 0000 0000 0000 1001
(logxor 12 5 7) ; 12 = 0000 0000 0000 0000 0000 0000 1100
; 5 = 0000 0000 0000 0000 0000 0000 0101
; 7 = 0000 0000 0000 0000 0000 0000 0111
=> 14 ; 14 = 0000 0000 0000 0000 0000 0000 1110
(lognot 5)
=> -6
;; 5 = 0000 0000 0000 0000 0000 0000 0101
;; becomes
;; -6 = 1111 1111 1111 1111 1111 1111 1010
These mathematical functions allow integers as well as floating point numbers as arguments.
(asin arg) is a number between -pi/2
and pi/2 (inclusive) whose sine is arg; if, however, arg
is out of range (outside [-1, 1]), then the result is a NaN.
(acos arg) is a number between 0 and pi
(inclusive) whose cosine is arg; if, however, arg
is out of range (outside [-1, 1]), then the result is a NaN.
(atan arg) is a number between -pi/2
and pi/2 (exclusive) whose tangent is arg.
(log10 x)
== (log x 10), at least approximately.
A deterministic computer program cannot generate true random numbers. For most purposes, pseudo-random numbers suffice. A series of pseudo-random numbers is generated in a deterministic fashion. The numbers are not truly random, but they have certain properties that mimic a random series. For example, all possible values occur equally often in a pseudo-random series.
In Emacs, pseudo-random numbers are generated from a "seed" number.
Starting from any given seed, the random function always
generates the same sequence of numbers. Emacs always starts with the
same seed value, so the sequence of values of random is actually
the same in each Emacs run! For example, in one operating system, the
first call to (random) after you start Emacs always returns
-1457731, and the second one always returns -7692030. This
repeatability is helpful for debugging.
If you want truly unpredictable random numbers, execute (random
t). This chooses a new seed based on the current time of day and on
Emacs's process ID number.
If limit is a positive integer, the value is chosen to be nonnegative and less than limit.
If limit is t, it means to choose a new seed based on the
current time of day and on Emacs's process ID number.
On some machines, any integer representable in Lisp may be the result
of random. On other machines, the result can never be larger
than a certain maximum or less than a certain (negative) minimum.
A string in Emacs Lisp is an array that contains an ordered sequence of characters. Strings are used as names of symbols, buffers, and files, to send messages to users, to hold text being copied between buffers, and for many other purposes. Because strings are so important, Emacs Lisp has many functions expressly for manipulating them. Emacs Lisp programs use strings more often than individual characters.
See section Putting Keyboard Events in Strings, for special considerations for strings of keyboard character events.
Strings in Emacs Lisp are arrays that contain an ordered sequence of characters. Characters are represented in Emacs Lisp as integers; whether an integer is a character or not is determined only by how it is used. Thus, strings really contain integers.
The length of a string (like any array) is fixed, and cannot be altered once the string exists. Strings in Lisp are not terminated by a distinguished character code. (By contrast, strings in C are terminated by a character with ASCII code 0.)
Since strings are arrays, and therefore sequences as well, you can
operate on them with the general array and sequence functions.
(See section Sequences, Arrays, and Vectors.) For example, you can access or
change individual characters in a string using the functions aref
and aset (see section Functions that Operate on Arrays).
There are two text representations for non-ASCII characters in Emacs strings (and in buffers): unibyte and multibyte (see section Text Representations). ASCII characters always occupy one byte in a string; in fact, there is no real difference between the two representation for a string which is all ASCII. For most Lisp programming, you don't need to be concerned with these two representations.
Sometimes key sequences are represented as strings. When a string is a key sequence, string elements in the range 128 to 255 represent meta characters (which are extremely large integers) rather than character codes in the range 128 to 255.
Strings cannot hold characters that have the hyper, super or alt modifiers; they can hold ASCII control characters, but no other control characters. They do not distinguish case in ASCII control characters. If you want to store such characters in a sequence, such as a key sequence, you must use a vector instead of a string. See section Character Type, for more information about representation of meta and other modifiers for keyboard input characters.
Strings are useful for holding regular expressions. You can also
match regular expressions against strings (see section Regular Expression Searching). The
functions match-string (see section Simple Match Data Access) and
replace-match (see section Replacing the Text That Matched) are useful for
decomposing and modifying strings based on regular expression matching.
Like a buffer, a string can contain text properties for the characters in it, as well as the characters themselves. See section Text Properties. All the Lisp primitives that copy text from strings to buffers or other strings also copy the properties of the characters being copied.
See section Text, for information about functions that display strings or copy them into buffers. See section Character Type, and section String Type, for information about the syntax of characters and strings. See section Non-ASCII Characters, for functions to convert between text representations and encode and decode character codes.
For more information about general sequence and array predicates, see section Sequences, Arrays, and Vectors, and section Arrays.
t if object is a string, nil
otherwise.
t if object is a string or a
character (i.e., an integer), nil otherwise.
The following functions create strings, either from scratch, or by putting strings together, or by taking them apart.
(make-string 5 ?x)
=> "xxxxx"
(make-string 0 ?x)
=> ""
Other functions to compare with this one include char-to-string
(see section Conversion of Characters and Strings), make-vector (see section Vectors), and
make-list (see section Building Cons Cells and Lists).
(string ?a ?b ?c)
=> "abc"
(substring "abcdefg" 0 3)
=> "abc"
Here the index for `a' is 0, the index for `b' is 1, and the
index for `c' is 2. Thus, three letters, `abc', are copied
from the string "abcdefg". The index 3 marks the character
position up to which the substring is copied. The character whose index
is 3 is actually the fourth character in the string.
A negative number counts from the end of the string, so that -1 signifies the index of the last character of the string. For example:
(substring "abcdefg" -3 -1)
=> "ef"
In this example, the index for `e' is -3, the index for `f' is -2, and the index for `g' is -1. Therefore, `e' and `f' are included, and `g' is excluded.
When nil is used as an index, it stands for the length of the
string. Thus,
(substring "abcdefg" -3 nil)
=> "efg"
Omitting the argument end is equivalent to specifying nil.
It follows that (substring string 0) returns a copy of all
of string.
(substring "abcdefg" 0)
=> "abcdefg"
But we recommend copy-sequence for this purpose (see section Sequences).
If the characters copied from string have text properties, the properties are copied into the new string also. See section Text Properties.
substring also allows vectors for the first argument.
For example:
(substring [a b (c) "d"] 1 3)
=> [b (c)]
A wrong-type-argument error is signaled if either start or
end is not an integer or nil. An args-out-of-range
error is signaled if start indicates a character following
end, or if either integer is out of range for string.
Contrast this function with buffer-substring (see section Examining Buffer Contents), which returns a string containing a portion of the text in
the current buffer. The beginning of a string is at index 0, but the
beginning of a buffer is at index 1.
concat receives no arguments, it
returns an empty string.
(concat "abc" "-def")
=> "abc-def"
(concat "abc" (list 120 121) [122])
=> "abcxyz"
;; nil is an empty sequence.
(concat "abc" nil "-def")
=> "abc-def"
(concat "The " "quick brown " "fox.")
=> "The quick brown fox."
(concat)
=> ""
The concat function always constructs a new string that is
not eq to any existing string.
When an argument is an integer (not a sequence of integers), it is
converted to a string of digits making up the decimal printed
representation of the integer. Don't use this feature; we plan
to eliminate it. If you already use this feature, change your programs
now! The proper way to convert an integer to a decimal number in this
way is with format (see section Formatting Strings) or
number-to-string (see section Conversion of Characters and Strings).
(concat 137)
=> "137"
(concat 54 321)
=> "54321"
For information about other concatenation functions, see the
description of mapconcat in section Mapping Functions,
vconcat in section Vectors, and append in section Building Cons Cells and Lists.
nil (or
omitted), the default is "[ \f\t\n\r\v]+".
For example,
(split-string "Soup is good food" "o")
=> ("S" "up is g" "" "d f" "" "d")
(split-string "Soup is good food" "o+")
=> ("S" "up is g" "d f" "d")
When there is a match adjacent to the beginning or end of the string, this does not cause a null string to appear at the beginning or end of the list:
(split-string "out to moo" "o+")
=> ("ut t" " m")
Empty matches do count, when not adjacent to another match:
(split-string "Soup is good food" "o*")
=>("S" "u" "p" " " "i" "s" " " "g" "d" " " "f" "d")
(split-string "Nice doggy!" "")
=>("N" "i" "c" "e" " " "d" "o" "g" "g" "y" "!")
The most basic way to alter the contents of an existing string is with
aset (see section Functions that Operate on Arrays). (aset string
idx char) stores char into string at index
idx. Each character occupies one or more bytes, and if char
needs a different number of bytes from the character already present at
that index, aset signals an error.
A more powerful function is store-substring:
Since it is impossible to change the length of an existing string, it is an error if obj doesn't fit within string's actual length, of if any new character requires a different number of bytes from the character currently present at that point in string.
t if the arguments represent the same
character, nil otherwise. This function ignores differences
in case if case-fold-search is non-nil.
(char-equal ?x ?x)
=> t
(let ((case-fold-search nil))
(char-equal ?x ?X))
=> nil
t if the characters of the two strings
match exactly; case is significant.
(string= "abc" "abc")
=> t
(string= "abc" "ABC")
=> nil
(string= "ab" "ABC")
=> nil
The function string= ignores the text properties of the two
strings. When equal (see section Equality Predicates) compares two
strings, it uses string=.
If the strings contain non-ASCII characters, and one is unibyte while the other is multibyte, then they cannot be equal. See section Text Representations.
string-equal is another name for string=.
t. If the lesser character is the one from
string2, then string1 is greater, and this function returns
nil. If the two strings match entirely, the value is nil.
Pairs of characters are compared according to their character codes. Keep in mind that lower case letters have higher numeric values in the ASCII character set than their upper case counterparts; digits and many punctuation characters have a lower numeric value than upper case letters. An ASCII character is less than any non-ASCII character; a unibyte non-ASCII character is always less than any multibyte non-ASCII character (see section Text Representations).
(string< "abc" "abd")
=> t
(string< "abd" "abc")
=> nil
(string< "123" "abc")
=> t
When the strings have different lengths, and they match up to the
length of string1, then the result is t. If they match up
to the length of string2, the result is nil. A string of
no characters is less than any other string.
(string< "" "abc")
=> t
(string< "ab" "abc")
=> t
(string< "abc" "")
=> nil
(string< "abc" "ab")
=> nil
(string< "" "")
=> nil
string-lessp is another name for string<.
The strings are both converted to multibyte for the comparison
(see section Text Representations) so that a unibyte string can be equal to
a multibyte string. If ignore-case is non-nil, then case
is ignored, so that upper case letters can be equal to lower case letters.
If the specified portions of the two strings match, the value is
t. Otherwise, the value is an integer which indicates how many
leading characters agree, and which string is less. Its absolute value
is one plus the number of characters that agree at the beginning of the
two strings. The sign is negative if string1 (or its specified
portion) is less.
assoc, except that key must be a
string, and comparison is done using compare-strings.
Case differences are ignored in this comparison.
assoc, except that key must be a
string, and comparison is done using compare-strings.
Case differences are significant.
See also compare-buffer-substrings in section Comparing Text, for
a way to compare text in buffers. The function string-match,
which matches a regular expression against a string, can be used
for a kind of string comparison; see section Regular Expression Searching.
This section describes functions for conversions between characters,
strings and integers. format and prin1-to-string
(see section Output Functions) can also convert Lisp objects into strings.
read-from-string (see section Input Functions) can "convert" a
string representation of a Lisp object into an object. The functions
string-make-multibyte and string-make-unibyte convert the
text representation of a string (see section Converting Text Representations).
See section Documentation, for functions that produce textual descriptions
of text characters and general input events
(single-key-description and text-char-description). These
functions are used primarily for making help messages.
string is more general. See section Creating Strings.
(string-to-char "ABC")
=> 65
(string-to-char "xyz")
=> 120
(string-to-char "")
=> 0
(string-to-char "\000")
=> 0
This function may be eliminated in the future if it does not seem useful enough to retain.
(number-to-string 256)
=> "256"
(number-to-string -23)
=> "-23"
(number-to-string -23.5)
=> "-23.5"
int-to-string is a semi-obsolete alias for this function.
See also the function format in section Formatting Strings.
nil, integers are converted
in that base. If base is nil, then base ten is used.
Floating point conversion always uses base ten; we have not implemented
other radices for floating point numbers, because that would be much
more work and does not seem useful.
The parsing skips spaces and tabs at the beginning of string, then reads as much of string as it can interpret as a number. (On some systems it ignores other whitespace at the beginning, not just spaces and tabs.) If the first character after the ignored whitespace is not a digit or a plus or minus sign, this function returns 0.
(string-to-number "256")
=> 256
(string-to-number "25 is a perfect square.")
=> 25
(string-to-number "X256")
=> 0
(string-to-number "-4.5")
=> -4.5
Here are some other functions that can convert to or from a string:
concat
concat can convert a vector or a list into a string.
See section Creating Strings.
vconcat
vconcat can convert a string into a vector. See section Functions for Vectors.
append
append can convert a string into a list. See section Building Cons Cells and Lists.
Formatting means constructing a string by substitution of computed values at various places in a constant string. This string controls how the other values are printed as well as where they appear; it is called a format string.
Formatting is often useful for computing messages to be displayed. In
fact, the functions message and error provide the same
formatting feature described here; they differ from format only
in how they use the result of formatting.
A format specification is a sequence of characters beginning with a
`%'. Thus, if there is a `%d' in string, the
format function replaces it with the printed representation of
one of the values to be formatted (one of the arguments objects).
For example:
(format "The value of fill-column is %d." fill-column)
=> "The value of fill-column is 72."
If string contains more than one format specification, the format specifications correspond with successive values from objects. Thus, the first format specification in string uses the first such value, the second format specification uses the second such value, and so on. Any extra format specifications (those for which there are no corresponding values) cause unpredictable behavior. Any extra values to be formatted are ignored.
Certain format specifications require values of particular types. If you supply a value that doesn't fit the requirements, an error is signaled.
Here is a table of valid format specifications:
princ, not
prin1---see section Output Functions). Thus, strings are represented
by their contents alone, with no `"' characters, and symbols appear
without `\' characters.
If there is no corresponding object, the empty string is used.
prin1---see section Output Functions). Thus, strings are enclosed in `"' characters, and
`\' characters appear where necessary before special characters.
If there is no corresponding object, the empty string is used.
(format "%%
%d" 30) returns "% 30".
Any other format character results in an `Invalid format operation' error.
Here are several examples:
(format "The name of this buffer is %s." (buffer-name))
=> "The name of this buffer is strings.texi."
(format "The buffer object prints as %s." (current-buffer))
=> "The buffer object prints as strings.texi."
(format "The octal value of %d is %o,
and the hex value is %x." 18 18 18)
=> "The octal value of 18 is 22,
and the hex value is 12."
All the specification characters allow an optional numeric prefix between the `%' and the character. The optional numeric prefix defines the minimum width for the object. If the printed representation of the object contains fewer characters than this, then it is padded. The padding is on the left if the prefix is positive (or starts with zero) and on the right if the prefix is negative. The padding character is normally a space, but if the numeric prefix starts with a zero, zeros are used for padding. Here are some examples of padding:
(format "%06d is padded on the left with zeros" 123)
=> "000123 is padded on the left with zeros"
(format "%-6d is padded on the right" 123)
=> "123 is padded on the right"
format never truncates an object's printed representation, no
matter what width you specify. Thus, you can use a numeric prefix to
specify a minimum spacing between columns with no risk of losing
information.
In the following three examples, `%7s' specifies a minimum width
of 7. In the first case, the string inserted in place of `%7s' has
only 3 letters, so 4 blank spaces are inserted for padding. In the
second case, the string "specification" is 13 letters wide but is
not truncated. In the third case, the padding is on the right.
(format "The word `%7s' actually has %d letters in it."
"foo" (length "foo"))
=> "The word ` foo' actually has 3 letters in it."
(format "The word `%7s' actually has %d letters in it."
"specification" (length "specification"))
=> "The word `specification' actually has 13 letters in it."
(format "The word `%-7s' actually has %d letters in it."
"foo" (length "foo"))
=> "The word `foo ' actually has 3 letters in it."
The character case functions change the case of single characters or of the contents of strings. The functions normally convert only alphabetic characters (the letters `A' through `Z' and `a' through `z', as well as non-ASCII letters); other characters are not altered. (You can specify a different case conversion mapping by specifying a case table---see section The Case Table.)
These functions do not modify the strings that are passed to them as arguments.
The examples below use the characters `X' and `x' which have ASCII codes 88 and 120 respectively.
When the argument to downcase is a string, the function creates
and returns a new string in which each letter in the argument that is
upper case is converted to lower case. When the argument to
downcase is a character, downcase returns the
corresponding lower case character. This value is an integer. If the
original character is lower case, or is not a letter, then the value
equals the original character.
(downcase "The cat in the hat")
=> "the cat in the hat"
(downcase ?X)
=> 120
When the argument to upcase is a string, the function creates
and returns a new string in which each letter in the argument that is
lower case is converted to upper case.
When the argument to upcase is a character, upcase
returns the corresponding upper case character. This value is an integer.
If the original character is upper case, or is not a letter, then the
value equals the original character.
(upcase "The cat in the hat")
=> "THE CAT IN THE HAT"
(upcase ?x)
=> 88
The definition of a word is any sequence of consecutive characters that are assigned to the word constituent syntax class in the current syntax table (See section Table of Syntax Classes).
When the argument to capitalize is a character, capitalize
has the same result as upcase.
(capitalize "The cat in the hat")
=> "The Cat In The Hat"
(capitalize "THE 77TH-HATTED CAT")
=> "The 77th-Hatted Cat"
(capitalize ?x)
=> 88
The definition of a word is any sequence of consecutive characters that are assigned to the word constituent syntax class in the current syntax table (See section Table of Syntax Classes).
(upcase-initials "The CAT in the hAt")
=> "The CAT In The HAt"
See section Comparison of Characters and Strings, for functions that compare strings; some of them ignore case differences, or can optionally ignore case differences.
You can customize case conversion by installing a special case table. A case table specifies the mapping between upper case and lower case letters. It affects both the case conversion functions for Lisp objects (see the previous section) and those that apply to text in the buffer (see section Case Changes). Each buffer has a case table; there is also a standard case table which is used to initialize the case table of new buffers.
A case table is a char-table (see section Char-Tables) whose subtype is
case-table. This char-table maps each character into the
corresponding lower case character. It has three extra slots, which
hold related tables:
In simple cases, all you need to specify is the mapping to lower-case; the three related tables will be calculated automatically from that one.
For some languages, upper and lower case letters are not in one-to-one correspondence. There may be two different lower case letters with the same upper case equivalent. In these cases, you need to specify the maps for both lower case and upper case.
The extra table canonicalize maps each character to a canonical equivalent; any two characters that are related by case-conversion have the same canonical equivalent character. For example, since `a' and `A' are related by case-conversion, they should have the same canonical equivalent character (which should be either `a' for both of them, or `A' for both of them).
The extra table equivalences is a map that cyclicly permutes each equivalence class (of characters with the same canonical equivalent). (For ordinary ASCII, this would map `a' into `A' and `A' into `a', and likewise for each set of equivalent characters.)
When you construct a case table, you can provide nil for
canonicalize; then Emacs fills in this slot from the lower case
and upper case mappings. You can also provide nil for
equivalences; then Emacs fills in this slot from
canonicalize. In a case table that is actually in use, those
components are non-nil. Do not try to specify equivalences
without also specifying canonicalize.
Here are the functions for working with case tables:
nil if object is a valid case
table.
The following three functions are convenient subroutines for packages that define non-ASCII character sets. They modify the specified case table case-table; they also modify the standard syntax table. See section Syntax Tables. Normally you would use these functions to change the standard case table.
A list represents a sequence of zero or more elements (which may be any Lisp objects). The important difference between lists and vectors is that two or more lists can share part of their structure; in addition, you can insert or delete elements in a list without copying the whole list.
Lists in Lisp are not a primitive data type; they are built up from cons cells. A cons cell is a data object that represents an ordered pair. It holds, or "points to," two Lisp objects, one labeled as the CAR, and the other labeled as the CDR. These names are traditional; see section Cons Cell and List Types. CDR is pronounced "could-er."
A list is a series of cons cells chained together, one cons cell per
element of the list. By convention, the CARs of the cons cells are
the elements of the list, and the CDRs are used to chain the list:
the CDR of each cons cell is the following cons cell. The CDR
of the last cons cell is nil. This asymmetry between the
CAR and the CDR is entirely a matter of convention; at the
level of cons cells, the CAR and CDR slots have the same
characteristics.
Because most cons cells are used as part of lists, the phrase list structure has come to mean any structure made out of cons cells.
The symbol nil is considered a list as well as a symbol; it is
the list with no elements. For convenience, the symbol nil is
considered to have nil as its CDR (and also as its
CAR).
The CDR of any nonempty list l is a list containing all the elements of l except the first.
A cons cell can be illustrated as a pair of boxes. The first box
represents the CAR and the second box represents the CDR.
Here is an illustration of the two-element list, (tulip lily),
made from two cons cells:
--------------- --------------- | car | cdr | | car | cdr | | tulip | o---------->| lily | nil | | | | | | | --------------- ---------------
Each pair of boxes represents a cons cell. Each box "refers to",
"points to" or "contains" a Lisp object. (These terms are
synonymous.) The first box, which describes the CAR of the first
cons cell, contains the symbol tulip. The arrow from the
CDR box of the first cons cell to the second cons cell indicates
that the CDR of the first cons cell is the second cons cell.
The same list can be illustrated in a different sort of box notation like this:
--- --- --- ---
| | |--> | | |--> nil
--- --- --- ---
| |
| |
--> tulip --> lily
Here is a more complex illustration, showing the three-element list,
((pine needles) oak maple), the first element of which is a
two-element list:
--- --- --- --- --- ---
| | |--> | | |--> | | |--> nil
--- --- --- --- --- ---
| | |
| | |
| --> oak --> maple
|
| --- --- --- ---
--> | | |--> | | |--> nil
--- --- --- ---
| |
| |
--> pine --> needles
The same list represented in the first box notation looks like this:
-------------- -------------- --------------
| car | cdr | | car | cdr | | car | cdr |
| o | o------->| oak | o------->| maple | nil |
| | | | | | | | | |
-- | --------- -------------- --------------
|
|
| -------------- ----------------
| | car | cdr | | car | cdr |
------>| pine | o------->| needles | nil |
| | | | | |
-------------- ----------------
See section Cons Cell and List Types, for the read and print syntax of cons cells and lists, and for more "box and arrow" illustrations of lists.
The following predicates test whether a Lisp object is an atom, is a
cons cell or is a list, or whether it is the distinguished object
nil. (Many of these predicates can be defined in terms of the
others, but they are used so often that it is worth having all of them.)
t if object is a cons cell, nil
otherwise. nil is not a cons cell, although it is a list.
t if object is an atom, nil
otherwise. All objects except cons cells are atoms. The symbol
nil is an atom and is also a list; it is the only Lisp object
that is both.
(atom object) == (not (consp object))
t if object is a cons cell or
nil. Otherwise, it returns nil.
(listp '(1))
=> t
(listp '())
=> t
listp: it returns t if
object is not a list. Otherwise, it returns nil.
(listp object) == (not (nlistp object))
t if object is nil, and
returns nil otherwise. This function is identical to not,
but as a matter of clarity we use null when object is
considered a list and not when it is considered a truth value
(see not in section Constructs for Combining Conditions).
(null '(1))
=> nil
(null '())
=> t
As a special case, if cons-cell is nil, then car
is defined to return nil; therefore, any list is a valid argument
for car. An error is signaled if the argument is not a cons cell
or nil.
(car '(a b c))
=> a
(car '())
=> nil
As a special case, if cons-cell is nil, then cdr
is defined to return nil; therefore, any list is a valid argument
for cdr. An error is signaled if the argument is not a cons cell
or nil.
(cdr '(a b c))
=> (b c)
(cdr '())
=> nil
nil otherwise. This is in contrast
to car, which signals an error if object is not a list.
(car-safe object)
==
(let ((x object))
(if (consp x)
(car x)
nil))
nil otherwise.
This is in contrast to cdr, which signals an error if
object is not a list.
(cdr-safe object)
==
(let ((x object))
(if (consp x)
(cdr x)
nil))
nil.
If n is negative, nth returns the first element of
list.
(nth 2 '(1 2 3 4))
=> 3
(nth 10 '(1 2 3 4))
=> nil
(nth -3 '(1 2 3 4))
=> 1
(nth n x) == (car (nthcdr n x))
The function elt is similar, but applies to any kind of sequence.
For historical reasons, it takes its arguments in the opposite order.
See section Sequences.
If n is zero or negative, nthcdr returns all of
list. If the length of list is n or less,
nthcdr returns nil.
(nthcdr 1 '(1 2 3 4))
=> (2 3 4)
(nthcdr 10 '(1 2 3 4))
=> nil
(nthcdr -3 '(1 2 3 4))
=> (1 2 3 4)
If list is not really a list, safe-length returns 0. If
list is circular, it returns a finite value which is at least the
number of distinct elements.
The most common way to compute the length of a list, when you are not
worried that it may be circular, is with length. See section Sequences.
(car (car cons-cell)).
(car (cdr cons-cell))
or (nth 1 cons-cell).
(cdr (car cons-cell)).
(cdr (cdr cons-cell))
or (nthcdr 2 cons-cell).
Many functions build lists, as lists reside at the very heart of Lisp.
cons is the fundamental list-building function; however, it is
interesting to note that list is used more times in the source
code for Emacs than cons.
(cons 1 '(2))
=> (1 2)
(cons 1 '())
=> (1)
(cons 1 2)
=> (1 . 2)
cons is often used to add a single element to the front of a
list. This is called consing the element onto the list. For
example:
(setq list (cons newelt list))
Note that there is no conflict between the variable named list
used in this example and the function named list described below;
any symbol can serve both purposes.
nil-terminated. If no objects
are given, the empty list is returned.
(list 1 2 3 4 5)
=> (1 2 3 4 5)
(list 1 2 '(3 4 5) 'foo)
=> (1 2 (3 4 5) foo)
(list)
=> nil
make-list with make-string (see section Creating Strings).
(make-list 3 'pigs)
=> (pigs pigs pigs)
(make-list 0 'pigs)
=> nil
nconc in section Functions that Rearrange Lists, for a way to join
lists with no copying.)
More generally, the final argument to append may be any Lisp
object. The final argument is not copied or converted; it becomes the
CDR of the last cons cell in the new list. If the final argument
is itself a list, then its elements become in effect elements of the
result list. If the final element is not a list, the result is a
"dotted list" since its final CDR is not nil as required
in a true list.
The append function also allows integers as arguments. It
converts them to strings of digits, making up the decimal print
representation of the integer, and then uses the strings instead of the
original integers. Don't use this feature; we plan to eliminate
it. If you already use this feature, change your programs now! The
proper way to convert an integer to a decimal number in this way is with
format (see section Formatting Strings) or number-to-string
(see section Conversion of Characters and Strings).
Here is an example of using append:
(setq trees '(pine oak))
=> (pine oak)
(setq more-trees (append '(maple birch) trees))
=> (maple birch pine oak)
trees
=> (pine oak)
more-trees
=> (maple birch pine oak)
(eq trees (cdr (cdr more-trees)))
=> t
You can see how append works by looking at a box diagram. The
variable trees is set to the list (pine oak) and then the
variable more-trees is set to the list (maple birch pine
oak). However, the variable trees continues to refer to the
original list:
more-trees trees
| |
| --- --- --- --- -> --- --- --- ---
--> | | |--> | | |--> | | |--> | | |--> nil
--- --- --- --- --- --- --- ---
| | | |
| | | |
--> maple -->birch --> pine --> oak
An empty sequence contributes nothing to the value returned by
append. As a consequence of this, a final nil argument
forces a copy of the previous argument:
trees
=> (pine oak)
(setq wood (append trees nil))
=> (pine oak)
wood
=> (pine oak)
(eq wood trees)
=> nil
This once was the usual way to copy a list, before the function
copy-sequence was invented. See section Sequences, Arrays, and Vectors.
Here we show the use of vectors and strings as arguments to append:
(append [a b] "cd" nil)
=> (a b 99 100)
With the help of apply (see section Calling Functions), we can append
all the lists in a list of lists:
(apply 'append '((a b c) nil (x y z) nil))
=> (a b c x y z)
If no sequences are given, nil is returned:
(append)
=> nil
Here are some examples where the final argument is not a list:
(append '(x y) 'z)
=> (x y . z)
(append '(x y) [z])
=> (x y . [z])
The second example shows that when the final argument is a sequence but not a list, the sequence's elements do not become elements of the resulting list. Instead, the sequence becomes the final CDR, like any other non-list final argument.
(setq x '(1 2 3 4))
=> (1 2 3 4)
(reverse x)
=> (4 3 2 1)
x
=> (1 2 3 4)
You can modify the CAR and CDR contents of a cons cell with the
primitives setcar and setcdr. We call these "destructive"
operations because they change existing list structure.
Common Lisp note: Common Lisp uses functions
rplacaandrplacdto alter list structure; they change structure the same way assetcarandsetcdr, but the Common Lisp functions return the cons cell whilesetcarandsetcdrreturn the new CAR or CDR.
setcar
Changing the CAR of a cons cell is done with setcar. When
used on a list, setcar replaces one element of a list with a
different element.
(setq x '(1 2))
=> (1 2)
(setcar x 4)
=> 4
x
=> (4 2)
When a cons cell is part of the shared structure of several lists, storing a new CAR into the cons changes one element of each of these lists. Here is an example:
;; Create two lists that are partly shared.
(setq x1 '(a b c))
=> (a b c)
(setq x2 (cons 'z (cdr x1)))
=> (z b c)
;; Replace the CAR of a shared link.
(setcar (cdr x1) 'foo)
=> foo
x1 ; Both lists are changed.
=> (a foo c)
x2
=> (z foo c)
;; Replace the CAR of a link that is not shared.
(setcar x1 'baz)
=> baz
x1 ; Only one list is changed.
=> (baz foo c)
x2
=> (z foo c)
Here is a graphical depiction of the shared structure of the two lists
in the variables x1 and x2, showing why replacing b
changes them both:
--- --- --- --- --- ---
x1---> | | |----> | | |--> | | |--> nil
--- --- --- --- --- ---
| --> | |
| | | |
--> a | --> b --> c
|
--- --- |
x2--> | | |--
--- ---
|
|
--> z
Here is an alternative form of box diagram, showing the same relationship:
x1:
-------------- -------------- --------------
| car | cdr | | car | cdr | | car | cdr |
| a | o------->| b | o------->| c | nil |
| | | -->| | | | | |
-------------- | -------------- --------------
|
x2: |
-------------- |
| car | cdr | |
| z | o----
| | |
--------------
The lowest-level primitive for modifying a CDR is setcdr:
Here is an example of replacing the CDR of a list with a different list. All but the first element of the list are removed in favor of a different sequence of elements. The first element is unchanged, because it resides in the CAR of the list, and is not reached via the CDR.
(setq x '(1 2 3))
=> (1 2 3)
(setcdr x '(4))
=> (4)
x
=> (1 4)
You can delete elements from the middle of a list by altering the
CDRs of the cons cells in the list. For example, here we delete
the second element, b, from the list (a b c), by changing
the CDR of the first cons cell:
(setq x1 '(a b c))
=> (a b c)
(setcdr x1 (cdr (cdr x1)))
=> (c)
x1
=> (a c)
Here is the result in box notation:
--------------------
| |
-------------- | -------------- | --------------
| car | cdr | | | car | cdr | -->| car | cdr |
| a | o----- | b | o-------->| c | nil |
| | | | | | | | |
-------------- -------------- --------------
The second cons cell, which previously held the element b, still
exists and its CAR is still b, but it no longer forms part
of this list.
It is equally easy to insert a new element by changing CDRs:
(setq x1 '(a b c))
=> (a b c)
(setcdr x1 (cons 'd (cdr x1)))
=> (d b c)
x1
=> (a d b c)
Here is this result in box notation:
-------------- ------------- -------------
| car | cdr | | car | cdr | | car | cdr |
| a | o | -->| b | o------->| c | nil |
| | | | | | | | | | |
--------- | -- | ------------- -------------
| |
----- --------
| |
| --------------- |
| | car | cdr | |
-->| d | o------
| | |
---------------
Here are some functions that rearrange lists "destructively" by modifying the CDRs of their component cons cells. We call these functions "destructive" because they chew up the original lists passed to them as arguments, relinking their cons cells to form a new list that is the returned value.
The function delq in the following section is another example
of destructive list manipulation.
append (see section Building Cons Cells and Lists), the lists are
not copied. Instead, the last CDR of each of the
lists is changed to refer to the following list. The last of the
lists is not altered. For example:
(setq x '(1 2 3))
=> (1 2 3)
(nconc x '(4 5))
=> (1 2 3 4 5)
x
=> (1 2 3 4 5)
Since the last argument of nconc is not itself modified, it is
reasonable to use a constant list, such as '(4 5), as in the
above example. For the same reason, the last argument need not be a
list:
(setq x '(1 2 3))
=> (1 2 3)
(nconc x 'z)
=> (1 2 3 . z)
x
=> (1 2 3 . z)
However, the other arguments (all but the last) must be lists.
A common pitfall is to use a quoted constant list as a non-last
argument to nconc. If you do this, your program will change
each time you run it! Here is what happens:
(defun add-foo (x) ; We want this function to add
(nconc '(foo) x)) ; foo to the front of its arg.
(symbol-function 'add-foo)
=> (lambda (x) (nconc (quote (foo)) x))
(setq xx (add-foo '(1 2))) ; It seems to work.
=> (foo 1 2)
(setq xy (add-foo '(3 4))) ; What happened?
=> (foo 1 2 3 4)
(eq xx xy)
=> t
(symbol-function 'add-foo)
=> (lambda (x) (nconc (quote (foo 1 2 3 4) x)))
reverse, nreverse alters its argument by reversing
the CDRs in the cons cells forming the list. The cons cell that
used to be the last one in list becomes the first cons cell of the
value.
For example:
(setq x '(1 2 3 4))
=> (1 2 3 4)
x
=> (1 2 3 4)
(nreverse x)
=> (4 3 2 1)
;; The cons cell that was first is now last.
x
=> (1)
To avoid confusion, we usually store the result of nreverse
back in the same variable which held the original list:
(setq x (nreverse x))
Here is the nreverse of our favorite example, (a b c),
presented graphically:
Original list head: Reversed list:
------------- ------------- ------------
| car | cdr | | car | cdr | | car | cdr |
| a | nil |<-- | b | o |<-- | c | o |
| | | | | | | | | | | | |
------------- | --------- | - | -------- | -
| | | |
------------- ------------
The argument predicate must be a function that accepts two
arguments. It is called with two elements of list. To get an
increasing order sort, the predicate should return t if the
first element is "less than" the second, or nil if not.
The comparison function predicate must give reliable results for
any given pair of arguments, at least within a single call to
sort. It must be antisymmetric; that is, if a is
less than b, b must not be less than a. It must be
transitive---that is, if a is less than b, and b
is less than c, then a must be less than c. If you
use a comparison function which does not meet these requirements, the
result of sort is unpredictable.
The destructive aspect of sort is that it rearranges the cons
cells forming list by changing CDRs. A nondestructive sort
function would create new cons cells to store the elements in their
sorted order. If you wish to make a sorted copy without destroying the
original, copy it first with copy-sequence and then sort.
Sorting does not change the CARs of the cons cells in list;
the cons cell that originally contained the element a in
list still has a in its CAR after sorting, but it now
appears in a different position in the list due to the change of
CDRs. For example:
(setq nums '(1 3 2 6 5 4 0))
=> (1 3 2 6 5 4 0)
(sort nums '<)
=> (0 1 2 3 4 5 6)
nums
=> (1 2 3 4 5 6)
Warning: Note that the list in nums no longer contains
0; this is the same cons cell that it was before, but it is no longer
the first one in the list. Don't assume a variable that formerly held
the argument now holds the entire sorted list! Instead, save the result
of sort and use that. Most often we store the result back into
the variable that held the original list:
(setq nums (sort nums '<))
See section Sorting Text, for more functions that perform sorting.
See documentation in section Access to Documentation Strings, for a
useful example of sort.
A list can represent an unordered mathematical set--simply consider a
value an element of a set if it appears in the list, and ignore the
order of the list. To form the union of two sets, use append (as
long as you don't mind having duplicate elements). Other useful
functions for sets include memq and delq, and their
equal versions, member and delete.
Common Lisp note: Common Lisp has functions
union(which avoids duplicate elements) andintersectionfor set operations, but GNU Emacs Lisp does not have them. You can write them in Lisp if you wish.
memq returns a list starting with the
first occurrence of object. Otherwise, it returns nil.
The letter `q' in memq says that it uses eq to
compare object against the elements of the list. For example:
(memq 'b '(a b c b a))
=> (b c b a)
(memq '(2) '((1) (2))) ; (2) and (2) are not eq.
=> nil
eq to
object from list. The letter `q' in delq says
that it uses eq to compare object against the elements of
the list, like memq.
When delq deletes elements from the front of the list, it does so
simply by advancing down the list and returning a sublist that starts
after those elements:
(delq 'a '(a b c)) == (cdr '(a b c))
When an element to be deleted appears in the middle of the list, removing it involves changing the CDRs (see section Altering the CDR of a List).
(setq sample-list '(a b c (4)))
=> (a b c (4))
(delq 'a sample-list)
=> (b c (4))
sample-list
=> (a b c (4))
(delq 'c sample-list)
=> (a b (4))
sample-list
=> (a b (4))
Note that (delq 'c sample-list) modifies sample-list to
splice out the third element, but (delq 'a sample-list) does not
splice anything--it just returns a shorter list. Don't assume that a
variable which formerly held the argument list now has fewer
elements, or that it still holds the original list! Instead, save the
result of delq and use that. Most often we store the result back
into the variable that held the original list:
(setq flowers (delq 'rose flowers))
In the following example, the (4) that delq attempts to match
and the (4) in the sample-list are not eq:
(delq '(4) sample-list)
=> (a c (4))
The following two functions are like memq and delq but use
equal rather than eq to compare elements. See section Equality Predicates.
member tests to see whether object is a member
of list, comparing members with object using equal.
If object is a member, member returns a list starting with
its first occurrence in list. Otherwise, it returns nil.
Compare this with memq:
(member '(2) '((1) (2))) ;(2)and(2)areequal. => ((2)) (memq '(2) '((1) (2))) ;(2)and(2)are noteq. => nil ;; Two strings with the same contents areequal. (member "foo" '("foo" "bar")) => ("foo" "bar")
equal to
object from list. It is to delq as member is
to memq: it uses equal to compare elements with
object, like member; when it finds an element that matches,
it removes the element just as delq would. For example:
(delete '(2) '((2) (1) (2)))
=> ((1))
Common Lisp note: The functions
memberanddeletein GNU Emacs Lisp are derived from Maclisp, not Common Lisp. The Common Lisp versions do not useequalto compare elements.
See also the function add-to-list, in section How to Alter a Variable Value,
for another way to add an element to a list stored in a variable.
An association list, or alist for short, records a mapping from keys to values. It is a list of cons cells called associations: the CAR of each cons cell is the key, and the CDR is the associated value.(1)
Here is an example of an alist. The key pine is associated with
the value cones; the key oak is associated with
acorns; and the key maple is associated with seeds.
'((pine . cones) (oak . acorns) (maple . seeds))
The associated values in an alist may be any Lisp objects; so may the
keys. For example, in the following alist, the symbol a is
associated with the number 1, and the string "b" is
associated with the list (2 3), which is the CDR of
the alist element:
((a . 1) ("b" 2 3))
Sometimes it is better to design an alist to store the associated value in the CAR of the CDR of the element. Here is an example:
'((rose red) (lily white) (buttercup yellow))
Here we regard red as the value associated with rose. One
advantage of this kind of alist is that you can store other related
information--even a list of other items--in the CDR of the
CDR. One disadvantage is that you cannot use rassq (see
below) to find the element containing a given value. When neither of
these considerations is important, the choice is a matter of taste, as
long as you are consistent about it for any given alist.
Note that the same alist shown above could be regarded as having the
associated value in the CDR of the element; the value associated
with rose would be the list (red).
Association lists are often used to record information that you might otherwise keep on a stack, since new associations may be added easily to the front of the list. When searching an association list for an association with a given key, the first one found is returned, if there is more than one.
In Emacs Lisp, it is not an error if an element of an association list is not a cons cell. The alist search functions simply ignore such elements. Many other versions of Lisp signal errors in such cases.
Note that property lists are similar to association lists in several respects. A property list behaves like an association list in which each key can occur only once. See section Property Lists, for a comparison of property lists and association lists.
equal (see section Equality Predicates). It returns nil if no
association in alist has a CAR equal to key.
For example:
(setq trees '((pine . cones) (oak . acorns) (maple . seeds)))
=> ((pine . cones) (oak . acorns) (maple . seeds))
(assoc 'oak trees)
=> (oak . acorns)
(cdr (assoc 'oak trees))
=> acorns
(assoc 'birch trees)
=> nil
Here is another example, in which the keys and values are not symbols:
(setq needles-per-cluster
'((2 "Austrian Pine" "Red Pine")
(3 "Pitch Pine")
(5 "White Pine")))
(cdr (assoc 3 needles-per-cluster))
=> ("Pitch Pine")
(cdr (assoc 2 needles-per-cluster))
=> ("Austrian Pine" "Red Pine")
The functions assoc-ignore-representation and
assoc-ignore-case are much like assoc except using
compare-strings to do the comparison. See section Comparison of Characters and Strings.
nil if no association in alist has
a CDR equal to value.
rassoc is like assoc except that it compares the CDR of
each alist association instead of the CAR. You can think of
this as "reverse assoc", finding the key for a given value.
assoc in that it returns the first
association for key in alist, but it makes the comparison
using eq instead of equal. assq returns nil
if no association in alist has a CAR eq to key.
This function is used more often than assoc, since eq is
faster than equal and most alists use symbols as keys.
See section Equality Predicates.
(setq trees '((pine . cones) (oak . acorns) (maple . seeds)))
=> ((pine . cones) (oak . acorns) (maple . seeds))
(assq 'pine trees)
=> (pine . cones)
On the other hand, assq is not usually useful in alists where the
keys may not be symbols:
(setq leaves
'(("simple leaves" . oak)
("compound leaves" . horsechestnut)))
(assq "simple leaves" leaves)
=> nil
(assoc "simple leaves" leaves)
=> ("simple leaves" . oak)
nil if no association in alist has
a CDR eq to value.
rassq is like assq except that it compares the CDR of
each alist association instead of the CAR. You can think of
this as "reverse assq", finding the key for a given value.
For example:
(setq trees '((pine . cones) (oak . acorns) (maple . seeds)))
(rassq 'acorns trees)
=> (oak . acorns)
(rassq 'spores trees)
=> nil
Note that rassq cannot search for a value stored in the CAR
of the CDR of an element:
(setq colors '((rose red) (lily white) (buttercup yellow)))
(rassq 'white colors)
=> nil
In this case, the CDR of the association (lily white) is not
the symbol white, but rather the list (white). This
becomes clearer if the association is written in dotted pair notation:
(lily white) == (lily . (white))
string-match with an alist that contains
regular expressions (see section Regular Expression Searching). If test is omitted
or nil, equal is used for comparison.
If an alist element matches key by this criterion,
then assoc-default returns a value based on this element.
If the element is a cons, then the value is the element's CDR.
Otherwise, the return value is default.
If no alist element matches key, assoc-default returns
nil.
(setq needles-per-cluster
'((2 . ("Austrian Pine" "Red Pine"))
(3 . ("Pitch Pine"))
(5 . ("White Pine"))))
=>
((2 "Austrian Pine" "Red Pine")
(3 "Pitch Pine")
(5 "White Pine"))
(setq copy (copy-alist needles-per-cluster))
=>
((2 "Austrian Pine" "Red Pine")
(3 "Pitch Pine")
(5 "White Pine"))
(eq needles-per-cluster copy)
=> nil
(equal needles-per-cluster copy)
=> t
(eq (car needles-per-cluster) (car copy))
=> nil
(cdr (car (cdr needles-per-cluster)))
=> ("Pitch Pine")
(eq (cdr (car (cdr needles-per-cluster)))
(cdr (car (cdr copy))))
=> t
This example shows how copy-alist makes it possible to change
the associations of one copy without affecting the other:
(setcdr (assq 3 copy) '("Martian Vacuum Pine"))
(cdr (assq 3 needles-per-cluster))
=> ("Pitch Pine")
Recall that the sequence type is the union of two other Lisp types: lists and arrays. In other words, any list is a sequence, and any array is a sequence. The common property that all sequences have is that each is an ordered collection of elements.
An array is a single primitive object that has a slot for each of its elements. All the elements are accessible in constant time, but the length of an existing array cannot be changed. Strings, vectors, char-tables and bool-vectors are the four types of arrays.
A list is a sequence of elements, but it is not a single primitive object; it is made of cons cells, one cell per element. Finding the nth element requires looking through n cons cells, so elements farther from the beginning of the list take longer to access. But it is possible to add elements to the list, or remove elements.
The following diagram shows the relationship between these types:
_____________________________________________
| |
| Sequence |
| ______ ________________________________ |
| | | | | |
| | List | | Array | |
| | | | ________ ________ | |
| |______| | | | | | | |
| | | Vector | | String | | |
| | |________| |________| | |
| | ____________ _____________ | |
| | | | | | | |
| | | Char-table | | Bool-vector | | |
| | |____________| |_____________| | |
| |________________________________| |
|_____________________________________________|
The elements of vectors and lists may be any Lisp objects. The elements of strings are all characters.
In Emacs Lisp, a sequence is either a list or an array. The common property of all sequences is that they are ordered collections of elements. This section describes functions that accept any kind of sequence.
t if object is a list, vector, or
string, nil otherwise.
nil), a wrong-type-argument error is
signaled.
See section Accessing Elements of Lists, for the related function safe-length.
(length '(1 2 3))
=> 3
(length ())
=> 0
(length "foobar")
=> 6
(length [1 2 3])
=> 3
(length (make-bool-vector 5 nil))
=> 5
nil;
otherwise, they trigger an args-out-of-range error.
(elt [1 2 3 4] 2)
=> 3
(elt '(1 2 3 4) 2)
=> 3
;; We use string to show clearly which character elt returns.
(string (elt "1234" 2))
=> "3"
(elt [1 2 3 4] 4)
error--> Args out of range: [1 2 3 4], 4
(elt [1 2 3 4] -1)
error--> Args out of range: [1 2 3 4], -1
This function generalizes aref (see section Functions that Operate on Arrays) and
nth (see section Accessing Elements of Lists).
Storing a new element into the copy does not affect the original
sequence, and vice versa. However, the elements of the new
sequence are not copies; they are identical (eq) to the elements
of the original. Therefore, changes made within these elements, as
found via the copied sequence, are also visible in the original
sequence.
If the sequence is a string with text properties, the property list in the copy is itself a copy, not shared with the original's property list. However, the actual values of the properties are shared. See section Text Properties.
See also append in section Building Cons Cells and Lists, concat in
section Creating Strings, and vconcat in section Vectors, for others
ways to copy sequences.
(setq bar '(1 2))
=> (1 2)
(setq x (vector 'foo bar))
=> [foo (1 2)]
(setq y (copy-sequence x))
=> [foo (1 2)]
(eq x y)
=> nil
(equal x y)
=> t
(eq (elt x 1) (elt y 1))
=> t
;; Replacing an element of one sequence.
(aset x 0 'quux)
x => [quux (1 2)]
y => [foo (1 2)]
;; Modifying the inside of a shared element.
(setcar (aref x 1) 69)
x => [quux (69 2)]
y => [foo (69 2)]
An array object has slots that hold a number of other Lisp objects, called the elements of the array. Any element of an array may be accessed in constant time. In contrast, an element of a list requires access time that is proportional to the position of the element in the list.
Emacs defines four types of array, all one-dimensional: strings, vectors, bool-vectors and char-tables. A vector is a general array; its elements can be any Lisp objects. A string is a specialized array; its elements must be characters (i.e., integers between 0 and 255). Each type of array has its own read syntax. See section String Type, and section Vector Type.
All four kinds of array share these characteristics:
aref and aset, respectively (see section Functions that Operate on Arrays).
When you create an array, other than a char-table, you must specify its length. You cannot specify the length of a char-table, because that is determined by the range of character codes.
In principle, if you want an array of text characters, you could use either a string or a vector. In practice, we always choose strings for such applications, for four reasons:
By contrast, for an array of keyboard input characters (such as a key sequence), a vector may be necessary, because many keyboard input characters are outside the range that will fit in a string. See section Key Sequence Input.
In this section, we describe the functions that accept all types of arrays.
t if object is an array (i.e., a
vector, a string, a bool-vector or a char-table).
(arrayp [a])
=> t
(arrayp "asdf")
=> t
(arrayp (syntax-table)) ;; A char-table.
=> t
(setq primes [2 3 5 7 11 13])
=> [2 3 5 7 11 13]
(aref primes 4)
=> 11
(aref "abcdefg" 1)
=> 98 ; `b' is ASCII code 98.
See also the function elt, in section Sequences.
(setq w [foo bar baz])
=> [foo bar baz]
(aset w 0 'fu)
=> fu
w
=> [fu bar baz]
(setq x "asdfasfd")
=> "asdfasfd"
(aset x 3 ?Z)
=> 90
x
=> "asdZasfd"
If array is a string and object is not a character, a
wrong-type-argument error results. If array is a string
and object is character, but object does not use the same
number of bytes as the character currently stored in (aref
object index), that is also an error. See section Splitting Characters.
(setq a [a b c d e f g])
=> [a b c d e f g]
(fillarray a 0)
=> [0 0 0 0 0 0 0]
a
=> [0 0 0 0 0 0 0]
(setq s "When in the course")
=> "When in the course"
(fillarray s ?-)
=> "------------------"
If array is a string and object is not a character, a
wrong-type-argument error results.
The general sequence functions copy-sequence and length
are often useful for objects known to be arrays. See section Sequences.
Arrays in Lisp, like arrays in most languages, are blocks of memory whose elements can be accessed in constant time. A vector is a general-purpose array of specified length; its elements can be any Lisp objects. (By contrast, a string can hold only characters as elements.) Vectors in Emacs are used for obarrays (vectors of symbols), and as part of keymaps (vectors of commands). They are also used internally as part of the representation of a byte-compiled function; if you print such a function, you will see a vector in it.
In Emacs Lisp, the indices of the elements of a vector start from zero and count up from there.
Vectors are printed with square brackets surrounding the elements.
Thus, a vector whose elements are the symbols a, b and
a is printed as [a b a]. You can write vectors in the
same way in Lisp input.
A vector, like a string or a number, is considered a constant for evaluation: the result of evaluating it is the same vector. This does not evaluate or even examine the elements of the vector. See section Self-Evaluating Forms.
Here are examples illustrating these principles:
(setq avector [1 two '(three) "four" [five]])
=> [1 two (quote (three)) "four" [five]]
(eval avector)
=> [1 two (quote (three)) "four" [five]]
(eq avector (eval avector))
=> t
Here are some functions that relate to vectors:
t if object is a vector.
(vectorp [a])
=> t
(vectorp "asdf")
=> nil
(vector 'foo 23 [bar baz] "rats")
=> [foo 23 [bar baz] "rats"]
(vector)
=> []
(setq sleepy (make-vector 9 'Z))
=> [Z Z Z Z Z Z Z Z Z]
The value is a newly constructed vector that is not eq to any
existing vector.
(setq a (vconcat '(A B C) '(D E F)))
=> [A B C D E F]
(eq a (vconcat a))
=> nil
(vconcat)
=> []
(vconcat [A B C] "aa" '(foo (6 7)))
=> [A B C 97 97 foo (6 7)]
The vconcat function also allows byte-code function objects as
arguments. This is a special feature to make it easy to access the entire
contents of a byte-code function object. See section Byte-Code Function Objects.
The vconcat function also allows integers as arguments. It
converts them to strings of digits, making up the decimal print
representation of the integer, and then uses the strings instead of the
original integers. Don't use this feature; we plan to eliminate
it. If you already use this feature, change your programs now! The
proper way to convert an integer to a decimal number in this way is with
format (see section Formatting Strings) or number-to-string
(see section Conversion of Characters and Strings).
For other concatenation functions, see mapconcat in section Mapping Functions, concat in section Creating Strings, and append
in section Building Cons Cells and Lists.
The append function provides a way to convert a vector into a
list with the same elements (see section Building Cons Cells and Lists):
(setq avector [1 two (quote (three)) "four" [five]])
=> [1 two (quote (three)) "four" [five]]
(append avector nil)
=> (1 two (quote (three)) "four" [five])
A char-table is much like a vector, except that it is indexed by
character codes. Any valid character code, without modifiers, can be
used as an index in a char-table. You can access a char-table's
elements with aref and aset, as with any array. In
addition, a char-table can have extra slots to hold additional
data not associated with particular character codes. Char-tables are
constants when evaluated.
Each char-table has a subtype which is a symbol. The subtype
has two purposes: to distinguish char-tables meant for different uses,
and to control the number of extra slots. For example, display tables
are char-tables with display-table as the subtype, and syntax
tables are char-tables with syntax-table as the subtype. A valid
subtype must have a char-table-extra-slots property which is an
integer between 0 and 10. This integer specifies the number of
extra slots in the char-table.
A char-table can have a parent. which is another char-table. If
it does, then whenever the char-table specifies nil for a
particular character c, it inherits the value specified in the
parent. In other words, (aref char-table c) returns
the value from the parent of char-table if char-table itself
specifies nil.
A char-table can also have a default value. If so, then
(aref char-table c) returns the default value
whenever the char-table does not specify any other non-nil value.
nil. You
cannot alter the subtype of a char-table after the char-table is
created.
There is no argument to specify the length of the char-table, because all char-tables have room for any valid character code as an index.
t if object is a char-table,
otherwise nil.
There is no special function to access the default value of a char-table.
To do that, use (char-table-range char-table nil).
nil or another char-table.
A char-table can specify an element value for a single character code; it can also specify a value for an entire character set.
nil
nil
t
char-table-range---either
a valid character or a generic character--and the value is
(char-table-range char-table key).
Overall, the key-value pairs passed to function describe all the values stored in char-table.
The return value is always nil; to make this function useful,
function should have side effects. For example,
here is how to examine each element of the syntax table:
(let (accumulator)
(map-char-table
#'(lambda (key value)
(setq accumulator
(cons (list key value) accumulator)))
(syntax-table))
accumulator)
=>
((475008 nil) (474880 nil) (474752 nil) (474624 nil)
... (5 (3)) (4 (3)) (3 (3)) (2 (3)) (1 (3)) (0 (3)))
A bool-vector is much like a vector, except that it stores only the
values t and nil. If you try to store any non-nil
value into an element of the bool-vector, the effect is to store
t there. As with all arrays, bool-vector indices start from 0,
and the length cannot be changed once the bool-vector is created.
Bool-vectors are constants when evaluated.
There are two special functions for working with bool-vectors; aside from that, you manipulate them with same functions used for other kinds of arrays.
t if object is a bool-vector,
and nil otherwise.
A symbol is an object with a unique name. This chapter describes symbols, their components, their property lists, and how they are created and interned. Separate chapters describe the use of symbols as variables and as function names; see section Variables, and section Functions. For the precise read syntax for symbols, see section Symbol Type.
You can test whether an arbitrary Lisp object is a symbol
with symbolp:
t if object is a symbol, nil
otherwise.
Each symbol has four components (or "cells"), each of which references another object:
symbol-name in section Creating and Interning Symbols.
symbol-value in
section Accessing Variable Values.
symbol-function in section Accessing Function Cell Contents.
symbol-plist in section Property Lists.
The print name cell always holds a string, and cannot be changed. The other three cells can be set individually to any specified Lisp object.
The print name cell holds the string that is the name of the symbol. Since symbols are represented textually by their names, it is important not to have two symbols with the same name. The Lisp reader ensures this: every time it reads a symbol, it looks for an existing symbol with the specified name before it creates a new one. (In GNU Emacs Lisp, this lookup uses a hashing algorithm and an obarray; see section Creating and Interning Symbols.)
In normal usage, the function cell usually contains a function
(see section Functions) or a macro (see section Macros), as that is what the
Lisp interpreter expects to see there (see section Evaluation). Keyboard
macros (see section Keyboard Macros), keymaps (see section Keymaps) and autoload
objects (see section Autoloading) are also sometimes stored in the function
cells of symbols. We often refer to "the function foo" when we
really mean the function stored in the function cell of the symbol
foo. We make the distinction only when necessary.
The property list cell normally should hold a correctly formatted property list (see section Property Lists), as a number of functions expect to see a property list there.
The function cell or the value cell may be void, which means
that the cell does not reference any object. (This is not the same
thing as holding the symbol void, nor the same as holding the
symbol nil.) Examining a function or value cell that is void
results in an error, such as `Symbol's value as variable is void'.
The four functions symbol-name, symbol-value,
symbol-plist, and symbol-function return the contents of
the four cells of a symbol. Here as an example we show the contents of
the four cells of the symbol buffer-file-name:
(symbol-name 'buffer-file-name)
=> "buffer-file-name"
(symbol-value 'buffer-file-name)
=> "/gnu/elisp/symbols.texi"
(symbol-plist 'buffer-file-name)
=> (variable-documentation 29529)
(symbol-function 'buffer-file-name)
=> #<subr buffer-file-name>
Because this symbol is the variable which holds the name of the file
being visited in the current buffer, the value cell contents we see are
the name of the source file of this chapter of the Emacs Lisp Manual.
The property list cell contains the list (variable-documentation
29529) which tells the documentation functions where to find the
documentation string for the variable buffer-file-name in the
`DOC-version' file. (29529 is the offset from the beginning
of the `DOC-version' file to where that documentation string
begins--see section Documentation Basics.) The function cell contains
the function for returning the name of the file.
buffer-file-name names a primitive function, which has no read
syntax and prints in hash notation (see section Primitive Function Type). A
symbol naming a function written in Lisp would have a lambda expression
(or a byte-code object) in this cell.
A definition in Lisp is a special form that announces your intention to use a certain symbol in a particular way. In Emacs Lisp, you can define a symbol as a variable, or define it as a function (or macro), or both independently.
A definition construct typically specifies a value or meaning for the symbol for one kind of use, plus documentation for its meaning when used in this way. Thus, when you define a symbol as a variable, you can supply an initial value for the variable, plus documentation for the variable.
defvar and defconst are special forms that define a
symbol as a global variable. They are documented in detail in
section Defining Global Variables. For defining user option variables that can
be customized, use defcustom (see section Writing Customization Definitions).
defun defines a symbol as a function, creating a lambda
expression and storing it in the function cell of the symbol. This
lambda expression thus becomes the function definition of the symbol.
(The term "function definition", meaning the contents of the function
cell, is derived from the idea that defun gives the symbol its
definition as a function.) defsubst and defalias are two
other ways of defining a function. See section Functions.
defmacro defines a symbol as a macro. It creates a macro
object and stores it in the function cell of the symbol. Note that a
given symbol can be a macro or a function, but not both at once, because
both macro and function definitions are kept in the function cell, and
that cell can hold only one Lisp object at any given time.
See section Macros.
In Emacs Lisp, a definition is not required in order to use a symbol
as a variable or function. Thus, you can make a symbol a global
variable with setq, whether you define it first or not. The real
purpose of definitions is to guide programmers and programming tools.
They inform programmers who read the code that certain symbols are
intended to be used as variables, or as functions. In addition,
utilities such as `etags' and `make-docfile' recognize
definitions, and add appropriate information to tag tables and the
`DOC-version' file. See section Access to Documentation Strings.
To understand how symbols are created in GNU Emacs Lisp, you must know how Lisp reads them. Lisp must ensure that it finds the same symbol every time it reads the same set of characters. Failure to do so would cause complete confusion.
When the Lisp reader encounters a symbol, it reads all the characters of the name. Then it "hashes" those characters to find an index in a table called an obarray. Hashing is an efficient method of looking something up. For example, instead of searching a telephone book cover to cover when looking up Jan Jones, you start with the J's and go from there. That is a simple version of hashing. Each element of the obarray is a bucket which holds all the symbols with a given hash code; to look for a given name, it is sufficient to look through all the symbols in the bucket for that name's hash code.
If a symbol with the desired name is found, the reader uses that symbol. If the obarray does not contain a symbol with that name, the reader makes a new symbol and adds it to the obarray. Finding or adding a symbol with a certain name is called interning it, and the symbol is then called an interned symbol.
Interning ensures that each obarray has just one symbol with any particular name. Other like-named symbols may exist, but not in the same obarray. Thus, the reader gets the same symbols for the same names, as long as you keep reading with the same obarray.
No obarray contains all symbols; in fact, some symbols are not in any obarray. They are called uninterned symbols. An uninterned symbol has the same four cells as other symbols; however, the only way to gain access to it is by finding it in some other object or as the value of a variable.
In Emacs Lisp, an obarray is actually a vector. Each element of the
vector is a bucket; its value is either an interned symbol whose name
hashes to that bucket, or 0 if the bucket is empty. Each interned
symbol has an internal link (invisible to the user) to the next symbol
in the bucket. Because these links are invisible, there is no way to
find all the symbols in an obarray except using mapatoms (below).
The order of symbols in a bucket is not significant.
In an empty obarray, every element is 0, and you can create an obarray
with (make-vector length 0). This is the only
valid way to create an obarray. Prime numbers as lengths tend
to result in good hashing; lengths one less than a power of two are also
good.
Do not try to put symbols in an obarray yourself. This does
not work--only intern can enter a symbol in an obarray properly.
Common Lisp note: In Common Lisp, a single symbol may be interned in several obarrays.
Most of the functions below take a name and sometimes an obarray as
arguments. A wrong-type-argument error is signaled if the name
is not a string, or if the obarray is not a vector.
(symbol-name 'foo)
=> "foo"
Warning: Changing the string by substituting characters does change the name of the symbol, but fails to update the obarray, so don't do it!
nil. In the example below,
the value of sym is not eq to foo because it is a
distinct uninterned symbol whose name is also `foo'.
(setq sym (make-symbol "foo"))
=> foo
(eq sym 'foo)
=> nil
intern
creates a new one, adds it to the obarray, and returns it. If
obarray is omitted, the value of the global variable
obarray is used.
(setq sym (intern "foo"))
=> foo
(eq sym 'foo)
=> t
(setq sym1 (intern "foo" other-obarray))
=> foo
(eq sym 'foo)
=> nil
Common Lisp note: In Common Lisp, you can intern an existing symbol in an obarray. In Emacs Lisp, you cannot do this, because the argument to
internmust be a string, not a symbol.
nil if obarray has no symbol with that name.
Therefore, you can use intern-soft to test whether a symbol with
a given name is already interned. If obarray is omitted, the
value of the global variable obarray is used.
(intern-soft "frazzle") ; No such symbol exists.
=> nil
(make-symbol "frazzle") ; Create an uninterned one.
=> frazzle
(intern-soft "frazzle") ; That one cannot be found.
=> nil
(setq sym (intern "frazzle")) ; Create an interned one.
=> frazzle
(intern-soft "frazzle") ; That one can be found!
=> frazzle
(eq sym 'frazzle) ; And it is the same one.
=> t
intern and
read.
nil. If obarray is
omitted, it defaults to the value of obarray, the standard
obarray for ordinary symbols.
(setq count 0)
=> 0
(defun count-syms (s)
(setq count (1+ count)))
=> count-syms
(mapatoms 'count-syms)
=> nil
count
=> 1871
See documentation in section Access to Documentation Strings, for another
example using mapatoms.
symbol is not actually in the obarray, unintern does
nothing. If obarray is nil, the current obarray is used.
If you provide a string instead of a symbol as symbol, it stands
for a symbol name. Then unintern deletes the symbol (if any) in
the obarray which has that name. If there is no such symbol,
unintern does nothing.
If unintern does delete a symbol, it returns t. Otherwise
it returns nil.
A property list (plist for short) is a list of paired elements stored in the property list cell of a symbol. Each of the pairs associates a property name (usually a symbol) with a property or value. Property lists are generally used to record information about a symbol, such as its documentation as a variable, the name of the file where it was defined, or perhaps even the grammatical class of the symbol (representing a word) in a language-understanding system.
Character positions in a string or buffer can also have property lists. See section Text Properties.
The property names and values in a property list can be any Lisp
objects, but the names are usually symbols. Property list functions
compare the property names using eq. Here is an example of a
property list, found on the symbol progn when the compiler is
loaded:
(lisp-indent-function 0 byte-compile byte-compile-progn)
Here lisp-indent-function and byte-compile are property
names, and the other two elements are the corresponding values.
Association lists (see section Association Lists) are very similar to property lists. In contrast to association lists, the order of the pairs in the property list is not significant since the property names must be distinct.
Property lists are better than association lists for attaching
information to various Lisp function names or variables. If your
program keeps all of its associations in one association list, it will
typically need to search that entire list each time it checks for an
association. This could be slow. By contrast, if you keep the same
information in the property lists of the function names or variables
themselves, each search will scan only the length of one property list,
which is usually short. This is why the documentation for a variable is
recorded in a property named variable-documentation. The byte
compiler likewise uses properties to record those functions needing
special treatment.
However, association lists have their own advantages. Depending on your application, it may be faster to add an association to the front of an association list than to update a property. All properties for a symbol are stored in the same property list, so there is a possibility of a conflict between different uses of a property name. (For this reason, it is a good idea to choose property names that are probably unique, such as by beginning the property name with the program's usual name-prefix for variables and functions.) An association list may be used like a stack where associations are pushed on the front of the list and later discarded; this is not possible with a property list.
(setplist 'foo '(a 1 b (2 3) c nil))
=> (a 1 b (2 3) c nil)
(symbol-plist 'foo)
=> (a 1 b (2 3) c nil)
For symbols in special obarrays, which are not used for ordinary purposes, it may make sense to use the property list cell in a nonstandard fashion; in fact, the abbrev mechanism does so (see section Abbrevs And Abbrev Expansion).
nil
is returned. Thus, there is no distinction between a value of
nil and the absence of the property.
The name property is compared with the existing property names
using eq, so any object is a legitimate property.
See put for an example.
put function returns value.
(put 'fly 'verb 'transitive)
=>'transitive
(put 'fly 'noun '(a buzzing little bug))
=> (a buzzing little bug)
(get 'fly 'verb)
=> transitive
(symbol-plist 'fly)
=> (verb transitive noun (a buzzing little bug))
These two functions are useful for manipulating property lists that are stored in places other than symbols:
(plist-get '(foo 4) 'foo)
=> 4
(setq my-plist '(bar t foo 4))
=> (bar t foo 4)
(setq my-plist (plist-put my-plist 'foo 69))
=> (bar t foo 69)
(setq my-plist (plist-put my-plist 'quux '(a)))
=> (bar t foo 69 quux (a))
You could define put in terms of plist-put as follows:
(defun put (symbol prop value)
(setplist symbol
(plist-put (symbol-plist symbol) prop value)))
The evaluation of expressions in Emacs Lisp is performed by the
Lisp interpreter---a program that receives a Lisp object as input
and computes its value as an expression. How it does this depends
on the data type of the object, according to rules described in this
chapter. The interpreter runs automatically to evaluate portions of
your program, but can also be called explicitly via the Lisp primitive
function eval.
A Lisp object that is intended for evaluation is called an expression or a form. The fact that expressions are data objects and not merely text is one of the fundamental differences between Lisp-like languages and typical programming languages. Any object can be evaluated, but in practice only numbers, symbols, lists and strings are evaluated very often.
It is very common to read a Lisp expression and then evaluate the
expression, but reading and evaluation are separate activities, and
either can be performed alone. Reading per se does not evaluate
anything; it converts the printed representation of a Lisp object to the
object itself. It is up to the caller of read whether this
object is a form to be evaluated, or serves some entirely different
purpose. See section Input Functions.
Do not confuse evaluation with command key interpretation. The
editor command loop translates keyboard input into a command (an
interactively callable function) using the active keymaps, and then
uses call-interactively to invoke the command. The execution of
the command itself involves evaluation if the command is written in
Lisp, but that is not a part of command key interpretation itself.
See section Command Loop.
Evaluation is a recursive process. That is, evaluation of a form may
call eval to evaluate parts of the form. For example, evaluation
of a function call first evaluates each argument of the function call,
and then evaluates each form in the function body. Consider evaluation
of the form (car x): the subform x must first be evaluated
recursively, so that its value can be passed as an argument to the
function car.
Evaluation of a function call ultimately calls the function specified in it. See section Functions. The execution of the function may itself work by evaluating the function definition; or the function may be a Lisp primitive implemented in C, or it may be a byte-compiled function (see section Byte Compilation).
The evaluation of forms takes place in a context called the environment, which consists of the current values and bindings of all Lisp variables.(2) Whenever a form refers to a variable without creating a new binding for it, the value of the variable's binding in the current environment is used. See section Variables.
Evaluation of a form may create new environments for recursive
evaluation by binding variables (see section Local Variables). These
environments are temporary and vanish by the time evaluation of the form
is complete. The form may also make changes that persist; these changes
are called side effects. An example of a form that produces side
effects is (setq foo 1).
The details of what evaluation means for each kind of form are described below (see section Kinds of Forms).
A Lisp object that is intended to be evaluated is called a form. How Emacs evaluates a form depends on its data type. Emacs has three different kinds of form that are evaluated differently: symbols, lists, and "all other types". This section describes all three kinds, one by one, starting with the "all other types" which are self-evaluating forms.
A self-evaluating form is any form that is not a list or symbol.
Self-evaluating forms evaluate to themselves: the result of evaluation
is the same object that was evaluated. Thus, the number 25 evaluates to
25, and the string "foo" evaluates to the string "foo".
Likewise, evaluation of a vector does not cause evaluation of the
elements of the vector--it returns the same vector with its contents
unchanged.
'123 ; A number, shown without evaluation.
=> 123
123 ; Evaluated as usual---result is the same.
=> 123
(eval '123) ; Evaluated ``by hand''---result is the same.
=> 123
(eval (eval '123)) ; Evaluating twice changes nothing.
=> 123
It is common to write numbers, characters, strings, and even vectors in Lisp code, taking advantage of the fact that they self-evaluate. However, it is quite unusual to do this for types that lack a read syntax, because there's no way to write them textually. It is possible to construct Lisp expressions containing these types by means of a Lisp program. Here is an example:
;; Build an expression containing a buffer object.
(setq print-exp (list 'print (current-buffer)))
=> (print #<buffer eval.texi>)
;; Evaluate it.
(eval print-exp)
-| #<buffer eval.texi>
=> #<buffer eval.texi>
When a symbol is evaluated, it is treated as a variable. The result is the variable's value, if it has one. If it has none (if its value cell is void), an error is signaled. For more information on the use of variables, see section Variables.
In the following example, we set the value of a symbol with
setq. Then we evaluate the symbol, and get back the value that
setq stored.
(setq a 123)
=> 123
(eval 'a)
=> 123
a
=> 123
The symbols nil and t are treated specially, so that the
value of nil is always nil, and the value of t is
always t; you cannot set or bind them to any other values. Thus,
these two symbols act like self-evaluating forms, even though
eval treats them like any other symbol. A symbol whose name
starts with `:' also self-evaluates in the same way; likewise,
its value ordinarily cannot be changed. See section Variables That Never Change.
A form that is a nonempty list is either a function call, a macro call, or a special form, according to its first element. These three kinds of forms are evaluated in different ways, described below. The remaining list elements constitute the arguments for the function, macro, or special form.
The first step in evaluating a nonempty list is to examine its first element. This element alone determines what kind of form the list is and how the rest of the list is to be processed. The first element is not evaluated, as it would be in some Lisp dialects such as Scheme.
If the first element of the list is a symbol then evaluation examines the symbol's function cell, and uses its contents instead of the original symbol. If the contents are another symbol, this process, called symbol function indirection, is repeated until it obtains a non-symbol. See section Naming a Function, for more information about using a symbol as a name for a function stored in the function cell of the symbol.
One possible consequence of this process is an infinite loop, in the
event that a symbol's function cell refers to the same symbol. Or a
symbol may have a void function cell, in which case the subroutine
symbol-function signals a void-function error. But if
neither of these things happens, we eventually obtain a non-symbol,
which ought to be a function or other suitable object.
More precisely, we should now have a Lisp function (a lambda
expression), a byte-code function, a primitive function, a Lisp macro, a
special form, or an autoload object. Each of these types is a case
described in one of the following sections. If the object is not one of
these types, the error invalid-function is signaled.
The following example illustrates the symbol indirection process. We
use fset to set the function cell of a symbol and
symbol-function to get the function cell contents
(see section Accessing Function Cell Contents). Specifically, we store the symbol car
into the function cell of first, and the symbol first into
the function cell of erste.
;; Build this function cell linkage: ;; ------------- ----- ------- ------- ;; | #<subr car> | <-- | car | <-- | first | <-- | erste | ;; ------------- ----- ------- -------
(symbol-function 'car)
=> #<subr car>
(fset 'first 'car)
=> car
(fset 'erste 'first)
=> first
(erste '(1 2 3)) ; Call the function referenced by erste.
=> 1
By contrast, the following example calls a function without any symbol function indirection, because the first element is an anonymous Lisp function, not a symbol.
((lambda (arg) (erste arg))
'(1 2 3))
=> 1
Executing the function itself evaluates its body; this does involve
symbol function indirection when calling erste.
The built-in function indirect-function provides an easy way to
perform symbol function indirection explicitly.
Here is how you could define indirect-function in Lisp:
(defun indirect-function (function)
(if (symbolp function)
(indirect-function (symbol-function function))
function))
If the first element of a list being evaluated is a Lisp function
object, byte-code object or primitive function object, then that list is
a function call. For example, here is a call to the function
+:
(+ 1 x)
The first step in evaluating a function call is to evaluate the
remaining elements of the list from left to right. The results are the
actual argument values, one value for each list element. The next step
is to call the function with this list of arguments, effectively using
the function apply (see section Calling Functions). If the function
is written in Lisp, the arguments are used to bind the argument
variables of the function (see section Lambda Expressions); then the forms
in the function body are evaluated in order, and the value of the last
body form becomes the value of the function call.
If the first element of a list being evaluated is a macro object, then the list is a macro call. When a macro call is evaluated, the elements of the rest of the list are not initially evaluated. Instead, these elements themselves are used as the arguments of the macro. The macro definition computes a replacement form, called the expansion of the macro, to be evaluated in place of the original form. The expansion may be any sort of form: a self-evaluating constant, a symbol, or a list. If the expansion is itself a macro call, this process of expansion repeats until some other sort of form results.
Ordinary evaluation of a macro call finishes by evaluating the expansion. However, the macro expansion is not necessarily evaluated right away, or at all, because other programs also expand macro calls, and they may or may not evaluate the expansions.
Normally, the argument expressions are not evaluated as part of computing the macro expansion, but instead appear as part of the expansion, so they are computed when the expansion is evaluated.
For example, given a macro defined as follows:
(defmacro cadr (x) (list 'car (list 'cdr x)))
an expression such as (cadr (assq 'handler list)) is a macro
call, and its expansion is:
(car (cdr (assq 'handler list)))
Note that the argument (assq 'handler list) appears in the
expansion.
See section Macros, for a complete description of Emacs Lisp macros.
A special form is a primitive function specially marked so that its arguments are not all evaluated. Most special forms define control structures or perform variable bindings--things which functions cannot do.
Each special form has its own rules for which arguments are evaluated and which are used without evaluation. Whether a particular argument is evaluated may depend on the results of evaluating other arguments.
Here is a list, in alphabetical order, of all of the special forms in Emacs Lisp with a reference to where each is described.
and
catch
catch and throw
cond
condition-case
defconst
defmacro
defun
defvar
function
if
interactive
let
let*
or
prog1
prog2
progn
quote
save-current-buffer
save-excursion
save-restriction
save-window-excursion
setq
setq-default
track-mouse
unwind-protect
while
with-output-to-temp-buffer
Common Lisp note: Here are some comparisons of special forms in GNU Emacs Lisp and Common Lisp.
setq,if, andcatchare special forms in both Emacs Lisp and Common Lisp.defunis a special form in Emacs Lisp, but a macro in Common Lisp.save-excursionis a special form in Emacs Lisp, but doesn't exist in Common Lisp.throwis a special form in Common Lisp (because it must be able to throw multiple values), but it is a function in Emacs Lisp (which doesn't have multiple values).
The autoload feature allows you to call a function or macro whose function definition has not yet been loaded into Emacs. It specifies which file contains the definition. When an autoload object appears as a symbol's function definition, calling that symbol as a function automatically loads the specified file; then it calls the real definition loaded from that file. See section Autoload.
The special form quote returns its single argument, as written,
without evaluating it. This provides a way to include constant symbols
and lists, which are not self-evaluating objects, in a program. (It is
not necessary to quote self-evaluating objects such as numbers, strings,
and vectors.)
Because quote is used so often in programs, Lisp provides a
convenient read syntax for it. An apostrophe character (`'')
followed by a Lisp object (in read syntax) expands to a list whose first
element is quote, and whose second element is the object. Thus,
the read syntax 'x is an abbreviation for (quote x).
Here are some examples of expressions that use quote:
(quote (+ 1 2))
=> (+ 1 2)
(quote foo)
=> foo
'foo
=> foo
''foo
=> (quote foo)
'(quote foo)
=> (quote foo)
['foo]
=> [(quote foo)]
Other quoting constructs include function (see section Anonymous Functions), which causes an anonymous lambda expression written in Lisp
to be compiled, and ``' (see section Backquote), which is used to quote
only part of a list, while computing and substituting other parts.
Most often, forms are evaluated automatically, by virtue of their
occurrence in a program being run. On rare occasions, you may need to
write code that evaluates a form that is computed at run time, such as
after reading a form from text being edited or getting one from a
property list. On these occasions, use the eval function.
The functions and variables described in this section evaluate forms, specify limits to the evaluation process, or record recently returned values. Loading a file also does evaluation (see section Loading).
Note: it is generally cleaner and more flexible to store a
function in a data structure, and call it with funcall or
apply, than to store an expression in the data structure and
evaluate it. Using functions provides the ability to pass information
to them as arguments.
Since eval is a function, the argument expression that appears
in a call to eval is evaluated twice: once as preparation before
eval is called, and again by the eval function itself.
Here is an example:
(setq foo 'bar)
=> bar
(setq bar 'baz)
=> baz
;; Here eval receives argument foo
(eval 'foo)
=> bar
;; Here eval receives argument bar, which is the value of foo
(eval foo)
=> baz
The number of currently active calls to eval is limited to
max-lisp-eval-depth (see below).
eval on them until the end of the region is
reached, or until an error is signaled and not handled.
If stream is non-nil, the values that result from
evaluating the expressions in the region are printed using stream.
See section Output Streams.
If read-function is non-nil, it should be a function, which
is used instead of read to read expressions one by one. This
function is called with one argument, the stream for reading input. You
can also use the variable load-read-function (see section How Programs Do Loading) to specify this function, but it is more robust to use the
read-function argument.
eval-region always returns nil.
eval-region except that it operates on the whole
buffer.
eval,
apply, and funcall before an error is signaled (with error
message "Lisp nesting exceeds max-lisp-eval-depth"). This limit,
with the associated error when it is exceeded, is one way that Lisp
avoids infinite recursion on an ill-defined function.
The depth limit counts internal uses of eval, apply, and
funcall, such as for calling the functions mentioned in Lisp
expressions, and recursive evaluation of function call arguments and
function body forms, as well as explicit calls in Lisp code.
The default value of this variable is 300. If you set it to a value less than 100, Lisp will reset it to 100 if the given value is reached. Entry to the Lisp debugger increases the value, if there is little room left, to make sure the debugger itself has room to execute.
max-specpdl-size provides another limit on nesting.
See section Local Variables.
(setq x 1)
=> 1
(list 'A (1+ 2) auto-save-default)
=> (A 3 t)
values
=> ((A 3 t) 1 ...)
This variable is useful for referring back to values of forms recently
evaluated. It is generally a bad idea to print the value of
values itself, since this may be very long. Instead, examine
particular elements, like this:
;; Refer to the most recent evaluation result.
(nth 0 values)
=> (A 3 t)
;; That put a new element on,
;; so all elements move back one.
(nth 1 values)
=> (A 3 t)
;; This gets the element that was next-to-most-recent
;; before this example.
(nth 3 values)
=> 1
A Lisp program consists of expressions or forms (see section Kinds of Forms). We control the order of execution of the forms by enclosing them in control structures. Control structures are special forms which control when, whether, or how many times to execute the forms they contain.
The simplest order of execution is sequential execution: first form a, then form b, and so on. This is what happens when you write several forms in succession in the body of a function, or at top level in a file of Lisp code--the forms are executed in the order written. We call this textual order. For example, if a function body consists of two forms a and b, evaluation of the function evaluates first a and then b, and the function's value is the value of b.
Explicit control structures make possible an order of execution other than sequential.
Emacs Lisp provides several kinds of control structure, including other varieties of sequencing, conditionals, iteration, and (controlled) jumps--all discussed below. The built-in control structures are special forms since their subforms are not necessarily evaluated or not evaluated sequentially. You can use macros to define your own control structure constructs (see section Macros).
Evaluating forms in the order they appear is the most common way
control passes from one form to another. In some contexts, such as in a
function body, this happens automatically. Elsewhere you must use a
control structure construct to do this: progn, the simplest
control construct of Lisp.
A progn special form looks like this:
(progn a b c ...)
and it says to execute the forms a, b, c and so on, in
that order. These forms are called the body of the progn form.
The value of the last form in the body becomes the value of the entire
progn.
In the early days of Lisp, progn was the only way to execute
two or more forms in succession and use the value of the last of them.
But programmers found they often needed to use a progn in the
body of a function, where (at that time) only one form was allowed. So
the body of a function was made into an "implicit progn":
several forms are allowed just as in the body of an actual progn.
Many other control structures likewise contain an implicit progn.
As a result, progn is not used as often as it used to be. It is
needed now most often inside an unwind-protect, and,
or, or in the then-part of an if.
(progn (print "The first form")
(print "The second form")
(print "The third form"))
-| "The first form"
-| "The second form"
-| "The third form"
=> "The third form"
Two other control constructs likewise evaluate a series of forms but return a different value:
(prog1 (print "The first form")
(print "The second form")
(print "The third form"))
-| "The first form"
-| "The second form"
-| "The third form"
=> "The first form"
Here is a way to remove the first element from a list in the variable
x, then return the value of that former element:
(prog1 (car x) (setq x (cdr x)))
(prog2 (print "The first form")
(print "The second form")
(print "The third form"))
-| "The first form"
-| "The second form"
-| "The third form"
=> "The second form"
Conditional control structures choose among alternatives. Emacs Lisp
has four conditional forms: if, which is much the same as in
other languages; when and unless, which are variants of
if; and cond, which is a generalized case statement.
if chooses between the then-form and the else-forms
based on the value of condition. If the evaluated condition is
non-nil, then-form is evaluated and the result returned.
Otherwise, the else-forms are evaluated in textual order, and the
value of the last one is returned. (The else part of if is
an example of an implicit progn. See section Sequencing.)
If condition has the value nil, and no else-forms are
given, if returns nil.
if is a special form because the branch that is not selected is
never evaluated--it is ignored. Thus, in the example below,
true is not printed because print is never called.
(if nil
(print 'true)
'very-false)
=> very-false
if where there are no else-forms,
and possibly several then-forms. In particular,
(when condition a b c)
is entirely equivalent to
(if condition (progn a b c) nil)
if where there is no then-form:
(unless condition a b c)
is entirely equivalent to
(if condition nil a b c)
cond chooses among an arbitrary number of alternatives. Each
clause in the cond must be a list. The CAR of this
list is the condition; the remaining elements, if any, the
body-forms. Thus, a clause looks like this:
(condition body-forms...)
cond tries the clauses in textual order, by evaluating the
condition of each clause. If the value of condition is
non-nil, the clause "succeeds"; then cond evaluates its
body-forms, and the value of the last of body-forms becomes
the value of the cond. The remaining clauses are ignored.
If the value of condition is nil, the clause "fails", so
the cond moves on to the following clause, trying its
condition.
If every condition evaluates to nil, so that every clause
fails, cond returns nil.
A clause may also look like this:
(condition)
Then, if condition is non-nil when tested, the value of
condition becomes the value of the cond form.
The following example has four clauses, which test for the cases where
the value of x is a number, string, buffer and symbol,
respectively:
(cond ((numberp x) x)
((stringp x) x)
((bufferp x)
(setq temporary-hack x) ; multiple body-forms
(buffer-name x)) ; in one clause
((symbolp x) (symbol-value x)))
Often we want to execute the last clause whenever none of the previous
clauses was successful. To do this, we use t as the
condition of the last clause, like this: (t
body-forms). The form t evaluates to t, which is
never nil, so this clause never fails, provided the cond
gets to it at all.
For example,
(cond ((eq a 'hack) 'foo)
(t "default"))
=> "default"
This expression is a cond which returns foo if the value
of a is hack, and returns the string "default" otherwise.
Any conditional construct can be expressed with cond or with
if. Therefore, the choice between them is a matter of style.
For example:
(if a b c) == (cond (a b) (t c))
This section describes three constructs that are often used together
with if and cond to express complicated conditions. The
constructs and and or can also be used individually as
kinds of multiple conditional constructs.
t if condition is nil, and nil otherwise.
The function not is identical to null, and we recommend
using the name null if you are testing for an empty list.
and special form tests whether all the conditions are
true. It works by evaluating the conditions one by one in the
order written.
If any of the conditions evaluates to nil, then the result
of the and must be nil regardless of the remaining
conditions; so and returns right away, ignoring the
remaining conditions.
If all the conditions turn out non-nil, then the value of
the last of them becomes the value of the and form.
Here is an example. The first condition returns the integer 1, which is
not nil. Similarly, the second condition returns the integer 2,
which is not nil. The third condition is nil, so the
remaining condition is never evaluated.
(and (print 1) (print 2) nil (print 3))
-| 1
-| 2
=> nil
Here is a more realistic example of using and:
(if (and (consp foo) (eq (car foo) 'x))
(message "foo is a list starting with x"))
Note that (car foo) is not executed if (consp foo) returns
nil, thus avoiding an error.
and can be expressed in terms of either if or cond.
For example:
(and arg1 arg2 arg3) == (if arg1 (if arg2 arg3)) == (cond (arg1 (cond (arg2 arg3))))
or special form tests whether at least one of the
conditions is true. It works by evaluating all the
conditions one by one in the order written.
If any of the conditions evaluates to a non-nil value, then
the result of the or must be non-nil; so or returns
right away, ignoring the remaining conditions. The value it
returns is the non-nil value of the condition just evaluated.
If all the conditions turn out nil, then the or
expression returns nil.
For example, this expression tests whether x is either 0 or
nil:
(or (eq x nil) (eq x 0))
Like the and construct, or can be written in terms of
cond. For example:
(or arg1 arg2 arg3)
==
(cond (arg1)
(arg2)
(arg3))
You could almost write or in terms of if, but not quite:
(if arg1 arg1
(if arg2 arg2
arg3))
This is not completely equivalent because it can evaluate arg1 or
arg2 twice. By contrast, (or arg1 arg2
arg3) never evaluates any argument more than once.
Iteration means executing part of a program repetitively. For
example, you might want to repeat some computation once for each element
of a list, or once for each integer from 0 to n. You can do this
in Emacs Lisp with the special form while:
while first evaluates condition. If the result is
non-nil, it evaluates forms in textual order. Then it
reevaluates condition, and if the result is non-nil, it
evaluates forms again. This process repeats until condition
evaluates to nil.
There is no limit on the number of iterations that may occur. The loop
will continue until either condition evaluates to nil or
until an error or throw jumps out of it (see section Nonlocal Exits).
The value of a while form is always nil.
(setq num 0)
=> 0
(while (< num 4)
(princ (format "Iteration %d." num))
(setq num (1+ num)))
-| Iteration 0.
-| Iteration 1.
-| Iteration 2.
-| Iteration 3.
=> nil
If you would like to execute something on each iteration before the
end-test, put it together with the end-test in a progn as the
first argument of while, as shown here:
(while (progn
(forward-line 1)
(not (looking-at "^$"))))
This moves forward one line and continues moving by lines until it
reaches an empty line. It is peculiar in that the while has no
body, just the end test (which also does the real work of moving point).
A nonlocal exit is a transfer of control from one point in a program to another remote point. Nonlocal exits can occur in Emacs Lisp as a result of errors; you can also use them under explicit control. Nonlocal exits unbind all variable bindings made by the constructs being exited.
catch and throw
Most control constructs affect only the flow of control within the
construct itself. The function throw is the exception to this
rule of normal program execution: it performs a nonlocal exit on
request. (There are other exceptions, but they are for error handling
only.) throw is used inside a catch, and jumps back to
that catch. For example:
(defun foo-outer ()
(catch 'foo
(foo-inner)))
(defun foo-inner ()
...
(if x
(throw 'foo t))
...)
The throw form, if executed, transfers control straight back to
the corresponding catch, which returns immediately. The code
following the throw is not executed. The second argument of
throw is used as the return value of the catch.
The function throw finds the matching catch based on the
first argument: it searches for a catch whose first argument is
eq to the one specified in the throw. If there is more
than one applicable catch, the innermost one takes precedence.
Thus, in the above example, the throw specifies foo, and
the catch in foo-outer specifies the same symbol, so that
catch is the applicable one (assuming there is no other matching
catch in between).
Executing throw exits all Lisp constructs up to the matching
catch, including function calls. When binding constructs such as
let or function calls are exited in this way, the bindings are
unbound, just as they are when these constructs exit normally
(see section Local Variables). Likewise, throw restores the buffer
and position saved by save-excursion (see section Excursions), and
the narrowing status saved by save-restriction and the window
selection saved by save-window-excursion (see section Window Configurations). It also runs any cleanups established with the
unwind-protect special form when it exits that form
(see section Cleaning Up from Nonlocal Exits).
The throw need not appear lexically within the catch
that it jumps to. It can equally well be called from another function
called within the catch. As long as the throw takes place
chronologically after entry to the catch, and chronologically
before exit from it, it has access to that catch. This is why
throw can be used in commands such as exit-recursive-edit
that throw back to the editor command loop (see section Recursive Editing).
Common Lisp note: Most other versions of Lisp, including Common Lisp, have several ways of transferring control nonsequentially:
return,return-from, andgo, for example. Emacs Lisp has onlythrow.
catch establishes a return point for the throw function.
The return point is distinguished from other such return points by
tag, which may be any Lisp object except nil. The argument
tag is evaluated normally before the return point is established.
With the return point in effect, catch evaluates the forms of the
body in textual order. If the forms execute normally, without
error or nonlocal exit, the value of the last body form is returned from
the catch.
If a throw is done within body specifying the same value
tag, the catch exits immediately; the value it returns is
whatever was specified as the second argument of throw.
throw is to return from a return point previously
established with catch. The argument tag is used to choose
among the various existing return points; it must be eq to the value
specified in the catch. If multiple return points match tag,
the innermost one is used.
The argument value is used as the value to return from that
catch.
If no return point is in effect with tag tag, then a no-catch
error is signaled with data (tag value).
catch and throw
One way to use catch and throw is to exit from a doubly
nested loop. (In most languages, this would be done with a "go to".)
Here we compute (foo i j) for i and j
varying from 0 to 9:
(defun search-foo ()
(catch 'loop
(let ((i 0))
(while (< i 10)
(let ((j 0))
(while (< j 10)
(if (foo i j)
(throw 'loop (list i j)))
(setq j (1+ j))))
(setq i (1+ i))))))
If foo ever returns non-nil, we stop immediately and return a
list of i and j. If foo always returns nil, the
catch returns normally, and the value is nil, since that
is the result of the while.
Here are two tricky examples, slightly different, showing two
return points at once. First, two return points with the same tag,
hack:
(defun catch2 (tag)
(catch tag
(throw 'hack 'yes)))
=> catch2
(catch 'hack
(print (catch2 'hack))
'no)
-| yes
=> no
Since both return points have tags that match the throw, it goes to
the inner one, the one established in catch2. Therefore,
catch2 returns normally with value yes, and this value is
printed. Finally the second body form in the outer catch, which is
'no, is evaluated and returned from the outer catch.
Now let's change the argument given to catch2:
(defun catch2 (tag)
(catch tag
(throw 'hack 'yes)))
=> catch2
(catch 'hack
(print (catch2 'quux))
'no)
=> yes
We still have two return points, but this time only the outer one has
the tag hack; the inner one has the tag quux instead.
Therefore, throw makes the outer catch return the value
yes. The function print is never called, and the
body-form 'no is never evaluated.
When Emacs Lisp attempts to evaluate a form that, for some reason, cannot be evaluated, it signals an error.
When an error is signaled, Emacs's default reaction is to print an error message and terminate execution of the current command. This is the right thing to do in most cases, such as if you type C-f at the end of the buffer.
In complicated programs, simple termination may not be what you want.
For example, the program may have made temporary changes in data
structures, or created temporary buffers that should be deleted before
the program is finished. In such cases, you would use
unwind-protect to establish cleanup expressions to be
evaluated in case of error. (See section Cleaning Up from Nonlocal Exits.) Occasionally, you may
wish the program to continue execution despite an error in a subroutine.
In these cases, you would use condition-case to establish
error handlers to recover control in case of error.
Resist the temptation to use error handling to transfer control from
one part of the program to another; use catch and throw
instead. See section Explicit Nonlocal Exits: catch and throw.
Most errors are signaled "automatically" within Lisp primitives
which you call for other purposes, such as if you try to take the
CAR of an integer or move forward a character at the end of the
buffer; you can also signal errors explicitly with the functions
error and signal.
Quitting, which happens when the user types C-g, is not considered an error, but it is handled almost like an error. See section Quitting.
format (see section Conversion of Characters and Strings) to
format-string and args.
These examples show typical uses of error:
(error "That is an error -- try something else")
error--> That is an error -- try something else
(error "You have committed %d errors" 10)
error--> You have committed 10 errors
error works by calling signal with two arguments: the
error symbol error, and a list containing the string returned by
format.
Warning: If you want to use your own string as an error message
verbatim, don't just write (error string). If string
contains `%', it will be interpreted as a format specifier, with
undesirable results. Instead, use (error "%s" string).
The argument error-symbol must be an error symbol---a symbol
bearing a property error-conditions whose value is a list of
condition names. This is how Emacs Lisp classifies different sorts of
errors.
The number and significance of the objects in data depends on
error-symbol. For example, with a wrong-type-arg error,
there should be two objects in the list: a predicate that describes the type
that was expected, and the object that failed to fit that type.
See section Error Symbols and Condition Names, for a description of error symbols.
Both error-symbol and data are available to any error
handlers that handle the error: condition-case binds a local
variable to a list of the form (error-symbol .
data) (see section Writing Code to Handle Errors). If the error is not handled,
these two values are used in printing the error message.
The function signal never returns (though in older Emacs versions
it could sometimes return).
(signal 'wrong-number-of-arguments '(x y))
error--> Wrong number of arguments: x, y
(signal 'no-such-error '("My unknown error condition"))
error--> peculiar error: "My unknown error condition"
Common Lisp note: Emacs Lisp has nothing like the Common Lisp concept of continuable errors.
When an error is signaled, signal searches for an active
handler for the error. A handler is a sequence of Lisp
expressions designated to be executed if an error happens in part of the
Lisp program. If the error has an applicable handler, the handler is
executed, and control resumes following the handler. The handler
executes in the environment of the condition-case that
established it; all functions called within that condition-case
have already been exited, and the handler cannot return to them.
If there is no applicable handler for the error, the current command is terminated and control returns to the editor command loop, because the command loop has an implicit handler for all kinds of errors. The command loop's handler uses the error symbol and associated data to print an error message.
An error that has no explicit handler may call the Lisp debugger. The
debugger is enabled if the variable debug-on-error (see section Entering the Debugger on an Error) is non-nil. Unlike error handlers, the debugger runs
in the environment of the error, so that you can examine values of
variables precisely as they were at the time of the error.
The usual effect of signaling an error is to terminate the command
that is running and return immediately to the Emacs editor command loop.
You can arrange to trap errors occurring in a part of your program by
establishing an error handler, with the special form
condition-case. A simple example looks like this:
(condition-case nil
(delete-file filename)
(error nil))
This deletes the file named filename, catching any error and
returning nil if an error occurs.
The second argument of condition-case is called the
protected form. (In the example above, the protected form is a
call to delete-file.) The error handlers go into effect when
this form begins execution and are deactivated when this form returns.
They remain in effect for all the intervening time. In particular, they
are in effect during the execution of functions called by this form, in
their subroutines, and so on. This is a good thing, since, strictly
speaking, errors can be signaled only by Lisp primitives (including
signal and error) called by the protected form, not by the
protected form itself.
The arguments after the protected form are handlers. Each handler
lists one or more condition names (which are symbols) to specify
which errors it will handle. The error symbol specified when an error
is signaled also defines a list of condition names. A handler applies
to an error if they have any condition names in common. In the example
above, there is one handler, and it specifies one condition name,
error, which covers all errors.
The search for an applicable handler checks all the established handlers
starting with the most recently established one. Thus, if two nested
condition-case forms offer to handle the same error, the inner of
the two will actually handle it.
If an error is handled by some condition-case form, this
ordinarily prevents the debugger from being run, even if
debug-on-error says this error should invoke the debugger.
See section Entering the Debugger on an Error. If you want to be able to debug errors that are
caught by a condition-case, set the variable
debug-on-signal to a non-nil value.
When an error is handled, control returns to the handler. Before this
happens, Emacs unbinds all variable bindings made by binding constructs
that are being exited and executes the cleanups of all
unwind-protect forms that are exited. Once control arrives at
the handler, the body of the handler is executed.
After execution of the handler body, execution returns from the
condition-case form. Because the protected form is exited
completely before execution of the handler, the handler cannot resume
execution at the point of the error, nor can it examine variable
bindings that were made within the protected form. All it can do is
clean up and proceed.
The condition-case construct is often used to trap errors that
are predictable, such as failure to open a file in a call to
insert-file-contents. It is also used to trap errors that are
totally unpredictable, such as when the program evaluates an expression
read from the user.
Error signaling and handling have some resemblance to throw and
catch, but they are entirely separate facilities. An error
cannot be caught by a catch, and a throw cannot be handled
by an error handler (though using throw when there is no suitable
catch signals an error that can be handled).
condition-case form; in this case, the condition-case has
no effect. The condition-case form makes a difference when an
error occurs during protected-form.
Each of the handlers is a list of the form (conditions
body...). Here conditions is an error condition name
to be handled, or a list of condition names; body is one or more
Lisp expressions to be executed when this handler handles an error.
Here are examples of handlers:
(error nil) (arith-error (message "Division by zero")) ((arith-error file-error) (message "Either division by zero or failure to open a file"))
Each error that occurs has an error symbol that describes what
kind of error it is. The error-conditions property of this
symbol is a list of condition names (see section Error Symbols and Condition Names). Emacs
searches all the active condition-case forms for a handler that
specifies one or more of these condition names; the innermost matching
condition-case handles the error. Within this
condition-case, the first applicable handler handles the error.
After executing the body of the handler, the condition-case
returns normally, using the value of the last form in the handler body
as the overall value.
The argument var is a variable. condition-case does not
bind this variable when executing the protected-form, only when it
handles an error. At that time, it binds var locally to an
error description, which is a list giving the particulars of the
error. The error description has the form (error-symbol
. data). The handler can refer to this list to decide what to
do. For example, if the error is for failure opening a file, the file
name is the second element of data---the third element of the
error description.
If var is nil, that means no variable is bound. Then the
error symbol and associated data are not available to the handler.
Here is an example of using condition-case to handle the error
that results from dividing by zero. The handler displays the error
message (but without a beep), then returns a very large number.
(defun safe-divide (dividend divisor)
(condition-case err
;; Protected form.
(/ dividend divisor)
;; The handler.
(arith-error ; Condition.
;; Display the usual message for this error.
(message "%s" (error-message-string err))
1000000)))
=> safe-divide
(safe-divide 5 0)
-| Arithmetic error: (arith-error)
=> 1000000
The handler specifies condition name arith-error so that it will handle only division-by-zero errors. Other kinds of errors will not be handled, at least not by this condition-case. Thus,
(safe-divide nil 3)
error--> Wrong type argument: number-or-marker-p, nil
Here is a condition-case that catches all kinds of errors,
including those signaled with error:
(setq baz 34)
=> 34
(condition-case err
(if (eq baz 35)
t
;; This is a call to the function error.
(error "Rats! The variable %s was %s, not 35" 'baz baz))
;; This is the handler; it is not a form.
(error (princ (format "The error was: %s" err))
2))
-| The error was: (error "Rats! The variable baz was 34, not 35")
=> 2
When you signal an error, you specify an error symbol to specify the kind of error you have in mind. Each error has one and only one error symbol to categorize it. This is the finest classification of errors defined by the Emacs Lisp language.
These narrow classifications are grouped into a hierarchy of wider
classes called error conditions, identified by condition
names. The narrowest such classes belong to the error symbols
themselves: each error symbol is also a condition name. There are also
condition names for more extensive classes, up to the condition name
error which takes in all kinds of errors. Thus, each error has
one or more condition names: error, the error symbol if that
is distinct from error, and perhaps some intermediate
classifications.
In order for a symbol to be an error symbol, it must have an
error-conditions property which gives a list of condition names.
This list defines the conditions that this kind of error belongs to.
(The error symbol itself, and the symbol error, should always be
members of this list.) Thus, the hierarchy of condition names is
defined by the error-conditions properties of the error symbols.
In addition to the error-conditions list, the error symbol
should have an error-message property whose value is a string to
be printed when that error is signaled but not handled. If the
error-message property exists, but is not a string, the error
message `peculiar error' is used.
Here is how we define a new error symbol, new-error:
(put 'new-error
'error-conditions
'(error my-own-errors new-error))
=> (error my-own-errors new-error)
(put 'new-error 'error-message "A new error")
=> "A new error"
This error has three condition names: new-error, the narrowest
classification; my-own-errors, which we imagine is a wider
classification; and error, which is the widest of all.
The error string should start with a capital letter but it should
not end with a period. This is for consistency with the rest of Emacs.
Naturally, Emacs will never signal new-error on its own; only
an explicit call to signal (see section How to Signal an Error) in your
code can do this:
(signal 'new-error '(x y))
error--> A new error: x, y
This error can be handled through any of the three condition names.
This example handles new-error and any other errors in the class
my-own-errors:
(condition-case foo
(bar nil t)
(my-own-errors nil))
The significant way that errors are classified is by their condition
names--the names used to match errors with handlers. An error symbol
serves only as a convenient way to specify the intended error message
and list of condition names. It would be cumbersome to give
signal a list of condition names rather than one error symbol.
By contrast, using only error symbols without condition names would
seriously decrease the power of condition-case. Condition names
make it possible to categorize errors at various levels of generality
when you write an error handler. Using error symbols alone would
eliminate all but the narrowest level of classification.
See section Standard Errors, for a list of all the standard error symbols and their conditions.
The unwind-protect construct is essential whenever you
temporarily put a data structure in an inconsistent state; it permits
you to make the data consistent again in the event of an error or throw.
unwind-protect executes the body with a guarantee that the
cleanup-forms will be evaluated if control leaves body, no
matter how that happens. The body may complete normally, or
execute a throw out of the unwind-protect, or cause an
error; in all cases, the cleanup-forms will be evaluated.
If the body forms finish normally, unwind-protect returns
the value of the last body form, after it evaluates the
cleanup-forms. If the body forms do not finish,
unwind-protect does not return any value in the normal sense.
Only the body is actually protected by the unwind-protect.
If any of the cleanup-forms themselves exits nonlocally (e.g., via
a throw or an error), unwind-protect is not
guaranteed to evaluate the rest of them. If the failure of one of the
cleanup-forms has the potential to cause trouble, then protect it
with another unwind-protect around that form.
The number of currently active unwind-protect forms counts,
together with the number of local variable bindings, against the limit
max-specpdl-size (see section Local Variables).
For example, here we make an invisible buffer for temporary use, and make sure to kill it before finishing:
(save-excursion
(let ((buffer (get-buffer-create " *temp*")))
(set-buffer buffer)
(unwind-protect
body
(kill-buffer buffer))))
You might think that we could just as well write (kill-buffer
(current-buffer)) and dispense with the variable buffer.
However, the way shown above is safer, if body happens to get an
error after switching to a different buffer! (Alternatively, you could
write another save-excursion around the body, to ensure that the
temporary buffer becomes current again in time to kill it.)
Emacs includes a standard macro called with-temp-buffer which
expands into more or less the code shown above (see section The Current Buffer).
Several of the macros defined in this manual use unwind-protect
in this way.
Here is an actual example taken from the file `ftp.el'. It
creates a process (see section Processes) to try to establish a connection
to a remote machine. As the function ftp-login is highly
susceptible to numerous problems that the writer of the function cannot
anticipate, it is protected with a form that guarantees deletion of the
process in the event of failure. Otherwise, Emacs might fill up with
useless subprocesses.
(let ((win nil))
(unwind-protect
(progn
(setq process (ftp-setup-buffer host file))
(if (setq win (ftp-login process host user password))
(message "Logged in")
(error "Ftp login failed")))
(or win (and process (delete-process process)))))
This example actually has a small bug: if the user types C-g to
quit, and the quit happens immediately after the function
ftp-setup-buffer returns but before the variable process is
set, the process will not be killed. There is no easy way to fix this bug,
but at least it is very unlikely.
A variable is a name used in a program to stand for a value. Nearly all programming languages have variables of some sort. In the text of a Lisp program, variables are written using the syntax for symbols.
In Lisp, unlike most programming languages, programs are represented primarily as Lisp objects and only secondarily as text. The Lisp objects used for variables are symbols: the symbol name is the variable name, and the variable's value is stored in the value cell of the symbol. The use of a symbol as a variable is independent of its use as a function name. See section Symbol Components.
The Lisp objects that constitute a Lisp program determine the textual form of the program--it is simply the read syntax for those Lisp objects. This is why, for example, a variable in a textual Lisp program is written using the read syntax for the symbol that represents the variable.
The simplest way to use a variable is globally. This means that the variable has just one value at a time, and this value is in effect (at least for the moment) throughout the Lisp system. The value remains in effect until you specify a new one. When a new value replaces the old one, no trace of the old value remains in the variable.
You specify a value for a symbol with setq. For example,
(setq x '(a b))
gives the variable x the value (a b). Note that
setq does not evaluate its first argument, the name of the
variable, but it does evaluate the second argument, the new value.
Once the variable has a value, you can refer to it by using the symbol by itself as an expression. Thus,
x => (a b)
assuming the setq form shown above has already been executed.
If you do set the same variable again, the new value replaces the old one:
x
=> (a b)
(setq x 4)
=> 4
x
=> 4
In Emacs Lisp, certain symbols normally evaluate to themselves. These
include nil and t, as well as any symbol whose name starts
with `:'. These symbols cannot be rebound, nor can their values be
changed. Any attempt to set or bind nil or t signals a
setting-constant error. The same is true for a symbol whose name
starts with `:', except that you are allowed to set such a symbol to
itself.
nil == 'nil
=> nil
(setq nil 500)
error--> Attempt to set constant symbol: nil
nil, you are allowed to set and bind symbols
whose names start with `:' as you wish. This is to make it
possible to run old Lisp programs which do that.
Global variables have values that last until explicitly superseded with new values. Sometimes it is useful to create variable values that exist temporarily--only until a certain part of the program finishes. These values are called local, and the variables so used are called local variables.
For example, when a function is called, its argument variables receive
new local values that last until the function exits. The let
special form explicitly establishes new local values for specified
variables; these last until exit from the let form.
Establishing a local value saves away the previous value (or lack of one) of the variable. When the life span of the local value is over, the previous value is restored. In the mean time, we say that the previous value is shadowed and not visible. Both global and local values may be shadowed (see section Scope).
If you set a variable (such as with setq) while it is local,
this replaces the local value; it does not alter the global value, or
previous local values, that are shadowed. To model this behavior, we
speak of a local binding of the variable as well as a local value.
The local binding is a conceptual place that holds a local value.
Entry to a function, or a special form such as let, creates the
local binding; exit from the function or from the let removes the
local binding. As long as the local binding lasts, the variable's value
is stored within it. Use of setq or set while there is a
local binding stores a different value into the local binding; it does
not create a new binding.
We also speak of the global binding, which is where (conceptually) the global value is kept.
A variable can have more than one local binding at a time (for
example, if there are nested let forms that bind it). In such a
case, the most recently created local binding that still exists is the
current binding of the variable. (This rule is called
dynamic scoping; see section Scoping Rules for Variable Bindings.) If there are no
local bindings, the variable's global binding is its current binding.
We sometimes call the current binding the most-local existing
binding, for emphasis. Ordinary evaluation of a symbol always returns
the value of its current binding.
The special forms let and let* exist to create
local bindings.
let-form
returns the value of the last form in forms.
Each of the bindings is either (i) a symbol, in which case
that symbol is bound to nil; or (ii) a list of the form
(symbol value-form), in which case symbol is
bound to the result of evaluating value-form. If value-form
is omitted, nil is used.
All of the value-forms in bindings are evaluated in the
order they appear and before binding any of the symbols to them.
Here is an example of this: Z is bound to the old value of
Y, which is 2, not the new value of Y, which is 1.
(setq Y 2)
=> 2
(let ((Y 1)
(Z Y))
(list Y Z))
=> (1 2)
let, but it binds each variable right
after computing its local value, before computing the local value for
the next variable. Therefore, an expression in bindings can
reasonably refer to the preceding symbols bound in this let*
form. Compare the following example with the example above for
let.
(setq Y 2)
=> 2
(let* ((Y 1)
(Z Y)) ; Use the just-established value of Y.
(list Y Z))
=> (1 1)
Here is a complete list of the other facilities that create local bindings:
condition-case (see section Errors).
Variables can also have buffer-local bindings (see section Buffer-Local Variables) and frame-local bindings (see section Frame-Local Variables); a few variables have terminal-local bindings (see section Multiple Displays). These kinds of bindings work somewhat like ordinary local bindings, but they are localized depending on "where" you are in Emacs, rather than localized in time.
unwind-protect cleanups (see section Nonlocal Exits)
that are allowed before signaling an error (with data "Variable
binding depth exceeds max-specpdl-size").
This limit, with the associated error when it is exceeded, is one way
that Lisp avoids infinite recursion on an ill-defined function.
max-lisp-eval-depth provides another limit on depth of nesting.
See section Eval.
The default value is 600. Entry to the Lisp debugger increases the value, if there is little room left, to make sure the debugger itself has room to execute.
If you have never given a symbol any value as a global variable, we
say that that symbol's global value is void. In other words, the
symbol's value cell does not have any Lisp object in it. If you try to
evaluate the symbol, you get a void-variable error rather than
a value.
Note that a value of nil is not the same as void. The symbol
nil is a Lisp object and can be the value of a variable just as any
other object can be; but it is a value. A void variable does not
have any value.
After you have given a variable a value, you can make it void once more
using makunbound.
void-variable, unless and until you set it again.
makunbound returns symbol.
(makunbound 'x) ; Make the global value of x void.
=> x
x
error--> Symbol's value as variable is void: x
If symbol is locally bound, makunbound affects the most
local existing binding. This is the only way a symbol can have a void
local binding, since all the constructs that create local bindings
create them with values. In this case, the voidness lasts at most as
long as the binding does; when the binding is removed due to exit from
the construct that made it, the previous local or global binding is
reexposed as usual, and the variable is no longer void unless the newly
reexposed binding was void all along.
(setq x 1) ; Put a value in the global binding.
=> 1
(let ((x 2)) ; Locally bind it.
(makunbound 'x) ; Void the local binding.
x)
error--> Symbol's value as variable is void: x
x ; The global binding is unchanged.
=> 1
(let ((x 2)) ; Locally bind it.
(let ((x 3)) ; And again.
(makunbound 'x) ; Void the innermost-local binding.
x)) ; And refer: it's void.
error--> Symbol's value as variable is void: x
(let ((x 2))
(let ((x 3))
(makunbound 'x)) ; Void inner binding, then remove it.
x) ; Now outer let binding is visible.
=> 2
A variable that has been made void with makunbound is
indistinguishable from one that has never received a value and has
always been void.
You can use the function boundp to test whether a variable is
currently void.
boundp returns t if variable (a symbol) is not void;
more precisely, if its current binding is not void. It returns
nil otherwise.
(boundp 'abracadabra) ; Starts out void.
=> nil
(let ((abracadabra 5)) ; Locally bind it.
(boundp 'abracadabra))
=> t
(boundp 'abracadabra) ; Still globally void.
=> nil
(setq abracadabra 5) ; Make it globally nonvoid.
=> 5
(boundp 'abracadabra)
=> t
You may announce your intention to use a symbol as a global variable
with a variable definition: a special form, either defconst
or defvar.
In Emacs Lisp, definitions serve three purposes. First, they inform
people who read the code that certain symbols are intended to be
used a certain way (as variables). Second, they inform the Lisp system
of these things, supplying a value and documentation. Third, they
provide information to utilities such as etags and
make-docfile, which create data bases of the functions and
variables in a program.
The difference between defconst and defvar is primarily
a matter of intent, serving to inform human readers of whether the value
should ever change. Emacs Lisp does not restrict the ways in which a
variable can be used based on defconst or defvar
declarations. However, it does make a difference for initialization:
defconst unconditionally initializes the variable, while
defvar initializes it only if it is void.
defvar.
If symbol is void and value is specified, defvar
evaluates it and sets symbol to the result. But if symbol
already has a value (i.e., it is not void), value is not even
evaluated, and symbol's value remains unchanged. If value
is omitted, the value of symbol is not changed in any case.
If symbol has a buffer-local binding in the current buffer,
defvar operates on the default value, which is buffer-independent,
not the current (buffer-local) binding. It sets the default value if
the default value is void. See section Buffer-Local Variables.
When you evaluate a top-level defvar form with C-M-x in
Emacs Lisp mode (eval-defun), a special feature of
eval-defun arranges to set the variable unconditionally, without
testing whether its value is void.
If the doc-string argument appears, it specifies the documentation
for the variable. (This opportunity to specify documentation is one of
the main benefits of defining the variable.) The documentation is
stored in the symbol's variable-documentation property. The
Emacs help functions (see section Documentation) look for this property.
If the first character of doc-string is `*', it means that
this variable is considered a user option. This lets users set the
variable conveniently using the commands set-variable and
edit-options. However, it is better to use defcustom
instead of defvar for user option variables, so you can specify
customization information. See section Writing Customization Definitions.
Here are some examples. This form defines foo but does not
initialize it:
(defvar foo)
=> foo
This example initializes the value of bar to 23, and gives
it a documentation string:
(defvar bar 23
"The normal weight of a bar.")
=> bar
The following form changes the documentation string for bar,
making it a user option, but does not change the value, since bar
already has a value. (The addition (1+ nil) would get an error
if it were evaluated, but since it is not evaluated, there is no error.)
(defvar bar (1+ nil)
"*The normal weight of a bar.")
=> bar
bar
=> 23
Here is an equivalent expression for the defvar special form:
(defvar symbol value doc-string)
==
(progn
(if (not (boundp 'symbol))
(setq symbol value))
(if 'doc-string
(put 'symbol 'variable-documentation 'doc-string))
'symbol)
The defvar form returns symbol, but it is normally used
at top level in a file where its value does not matter.
defconst.
defconst always evaluates value, and sets the value of
symbol to the result if value is given. If symbol
does have a buffer-local binding in the current buffer, defconst
sets the default value, not the buffer-local value. (But you should not
be making buffer-local bindings for a symbol that is defined with
defconst.)
Here, pi is a constant that presumably ought not to be changed
by anyone (attempts by the Indiana State Legislature notwithstanding).
As the second form illustrates, however, this is only advisory.
(defconst pi 3.1415 "Pi to five places.")
=> pi
(setq pi 3)
=> pi
pi
=> 3
t if variable is a user option--a
variable intended to be set by the user for customization--and
nil otherwise. (Variables other than user options exist for the
internal purposes of Lisp programs, and users need not know about them.)
User option variables are distinguished from other variables by the
first character of the variable-documentation property. If the
property exists and is a string, and its first character is `*',
then the variable is a user option.
If a user option variable has a variable-interactive property,
the set-variable command uses that value to control reading the
new value for the variable. The property's value is used as if it were
to interactive (see section Using interactive). However, this feature
is largely obsoleted by defcustom (see section Writing Customization Definitions).
Warning: If the defconst and defvar special
forms are used while the variable has a local binding, they set the
local binding's value; the global binding is not changed. This is not
what we really want. To prevent it, use these special forms at top
level in a file, where normally no local binding is in effect, and make
sure to load the file before making a local binding for the variable.
When defining and initializing a variable that holds a complicated
value (such as a keymap with bindings in it), it's best to put the
entire computation of the value into the defvar, like this:
(defvar my-mode-map
(let ((map (make-sparse-keymap)))
(define-key map "\C-c\C-a" 'my-command)
...
map)
docstring)
This method has several benefits. First, if the user quits while
loading the file, the variable is either still uninitialized or
initialized properly, never in-between. If it is still uninitialized,
reloading the file will initialize it properly. Second, reloading the
file once the variable is initialized will not alter it; that is
important if the user has run hooks to alter part of the contents (such
as, to rebind keys). Third, evaluating the defvar form with
C-M-x will reinitialize the map completely.
Putting so much code in the defvar form has one disadvantage:
it puts the documentation string far away from the line which names the
variable. Here's a safe way to avoid that:
(defvar my-mode-map nil
docstring)
(if my-mode-map
nil
(let ((map (make-sparse-keymap)))
(define-key my-mode-map "\C-c\C-a" 'my-command)
...
(setq my-mode-map map)))
This has all the same advantages as putting the initialization inside
the defvar, except that you must type C-M-x twice, once on
each form, if you do want to reinitialize the variable.
But be careful not to write the code like this:
(defvar my-mode-map nil
docstring)
(if my-mode-map
nil
(setq my-mode-map (make-sparse-keymap))
(define-key my-mode-map "\C-c\C-a" 'my-command)
...)
This code sets the variable, then alters it, but it does so in more than
one step. If the user quits just after the setq, that leaves the
variable neither correctly initialized nor void nor nil. Once
that happens, reloading the file will not initialize the variable; it
will remain incomplete.
The usual way to reference a variable is to write the symbol which
names it (see section Symbol Forms). This requires you to specify the
variable name when you write the program. Usually that is exactly what
you want to do. Occasionally you need to choose at run time which
variable to reference; then you can use symbol-value.
(setq abracadabra 5)
=> 5
(setq foo 9)
=> 9
;; Here the symbol abracadabra
;; is the symbol whose value is examined.
(let ((abracadabra 'foo))
(symbol-value 'abracadabra))
=> foo
;; Here the value of abracadabra,
;; which is foo,
;; is the symbol whose value is examined.
(let ((abracadabra 'foo))
(symbol-value abracadabra))
=> 9
(symbol-value 'abracadabra)
=> 5
A void-variable error is signaled if the current binding of
symbol is void.
The usual way to change the value of a variable is with the special
form setq. When you need to compute the choice of variable at
run time, use the function set.
setq does not evaluate symbol; it sets the symbol that you
write. We say that this argument is automatically quoted. The
`q' in setq stands for "quoted."
The value of the setq form is the value of the last form.
(setq x (1+ 2))
=> 3
x ; x now has a global value.
=> 3
(let ((x 5))
(setq x 6) ; The local binding of x is set.
x)
=> 6
x ; The global value is unchanged.
=> 3
Note that the first form is evaluated, then the first symbol is set, then the second form is evaluated, then the second symbol is set, and so on:
(setq x 10 ; Notice thatxis set before y (1+ x)) ; the value ofyis computed. => 11
set is a function, the expression written for
symbol is evaluated to obtain the symbol to set.
The most-local existing binding of the variable is the binding that is set; shadowed bindings are not affected.
(set one 1)
error--> Symbol's value as variable is void: one
(set 'one 1)
=> 1
(set 'two 'one)
=> one
(set two 2) ; two evaluates to symbol one.
=> 2
one ; So it is one that was set.
=> 2
(let ((one 1)) ; This binding of one is set,
(set 'one 3) ; not the global value.
one)
=> 3
one
=> 2
If symbol is not actually a symbol, a wrong-type-argument
error is signaled.
(set '(x y) 'z) error--> Wrong type argument: symbolp, (x y)
Logically speaking, set is a more fundamental primitive than
setq. Any use of setq can be trivially rewritten to use
set; setq could even be defined as a macro, given the
availability of set. However, set itself is rarely used;
beginners hardly need to know about it. It is useful only for choosing
at run time which variable to set. For example, the command
set-variable, which reads a variable name from the user and then
sets the variable, needs to use set.
Common Lisp note: In Common Lisp,
setalways changes the symbol's "special" or dynamic value, ignoring any lexical bindings. In Emacs Lisp, all variables and all bindings are dynamic, sosetalways affects the most local existing binding.
One other function for setting a variable is designed to add an element to a list if it is not already present in the list.
The argument symbol is not implicitly quoted; add-to-list
is an ordinary function, like set and unlike setq. Quote
the argument yourself if that is what you want.
Here's a scenario showing how to use add-to-list:
(setq foo '(a b))
=> (a b)
(add-to-list 'foo 'c) ;; Add c.
=> (c a b)
(add-to-list 'foo 'b) ;; No effect.
=> (c a b)
foo ;; foo was changed.
=> (c a b)
An equivalent expression for (add-to-list 'var
value) is this:
(or (member value var)
(setq var (cons value var)))
A given symbol foo can have several local variable bindings,
established at different places in the Lisp program, as well as a global
binding. The most recently established binding takes precedence over
the others.
Local bindings in Emacs Lisp have indefinite scope and dynamic extent. Scope refers to where textually in the source code the binding can be accessed. Indefinite scope means that any part of the program can potentially access the variable binding. Extent refers to when, as the program is executing, the binding exists. Dynamic extent means that the binding lasts as long as the activation of the construct that established it.
The combination of dynamic extent and indefinite scope is called dynamic scoping. By contrast, most programming languages use lexical scoping, in which references to a local variable must be located textually within the function or block that binds the variable.
Common Lisp note: Variables declared "special" in Common Lisp are dynamically scoped, like all variables in Emacs Lisp.
Emacs Lisp uses indefinite scope for local variable bindings. This means that any function anywhere in the program text might access a given binding of a variable. Consider the following function definitions:
(defun binder (x) ;xis bound inbinder. (foo 5)) ;foois some other function. (defun user () ;xis used ``free'' inuser. (list x))
In a lexically scoped language, the binding of x in
binder would never be accessible in user, because
user is not textually contained within the function
binder. However, in dynamically scoped Emacs Lisp, user
may or may not refer to the binding of x established in
binder, depending on circumstances:
user directly without calling binder at all,
then whatever binding of x is found, it cannot come from
binder.
foo as follows and then call binder, then the
binding made in binder will be seen in user:
(defun foo (lose) (user))
foo as follows and then call binder,
then the binding made in binder will not be seen in
user:
(defun foo (x) (user))Here, when
foo is called by binder, it binds x.
(The binding in foo is said to shadow the one made in
binder.) Therefore, user will access the x bound
by foo instead of the one bound by binder.
Emacs Lisp uses dynamic scoping because simple implementations of lexical scoping are slow. In addition, every Lisp system needs to offer dynamic scoping at least as an option; if lexical scoping is the norm, there must be a way to specify dynamic scoping instead for a particular variable. It might not be a bad thing for Emacs to offer both, but implementing it with dynamic scoping only was much easier.
Extent refers to the time during program execution that a variable name is valid. In Emacs Lisp, a variable is valid only while the form that bound it is executing. This is called dynamic extent. "Local" or "automatic" variables in most languages, including C and Pascal, have dynamic extent.
One alternative to dynamic extent is indefinite extent. This means that a variable binding can live on past the exit from the form that made the binding. Common Lisp and Scheme, for example, support this, but Emacs Lisp does not.
To illustrate this, the function below, make-add, returns a
function that purports to add n to its own argument m. This
would work in Common Lisp, but it does not do the job in Emacs Lisp,
because after the call to make-add exits, the variable n
is no longer bound to the actual argument 2.
(defun make-add (n)
(function (lambda (m) (+ n m)))) ; Return a function.
=> make-add
(fset 'add2 (make-add 2)) ; Define function add2
; with (make-add 2).
=> (lambda (m) (+ n m))
(add2 4) ; Try to add 2 to 4.
error--> Symbol's value as variable is void: n
Some Lisp dialects have "closures", objects that are like functions but record additional variable bindings. Emacs Lisp does not have closures.
A simple sample implementation (which is not how Emacs Lisp actually works) may help you understand dynamic binding. This technique is called deep binding and was used in early Lisp systems.
Suppose there is a stack of bindings, which are variable-value pairs.
At entry to a function or to a let form, we can push bindings
onto the stack for the arguments or local variables created there. We
can pop those bindings from the stack at exit from the binding
construct.
We can find the value of a variable by searching the stack from top to bottom for a binding for that variable; the value from that binding is the value of the variable. To set the variable, we search for the current binding, then store the new value into that binding.
As you can see, a function's bindings remain in effect as long as it continues execution, even during its calls to other functions. That is why we say the extent of the binding is dynamic. And any other function can refer to the bindings, if it uses the same variables while the bindings are in effect. That is why we say the scope is indefinite.
The actual implementation of variable scoping in GNU Emacs Lisp uses a technique called shallow binding. Each variable has a standard place in which its current value is always found--the value cell of the symbol.
In shallow binding, setting the variable works by storing a value in the value cell. Creating a new binding works by pushing the old value (belonging to a previous binding) onto a stack, and storing the new local value in the value cell. Eliminating a binding works by popping the old value off the stack, into the value cell.
We use shallow binding because it has the same results as deep binding, but runs faster, since there is never a need to search for a binding.
Binding a variable in one function and using it in another is a powerful technique, but if used without restraint, it can make programs hard to understand. There are two clean ways to use this technique:
case-fold-search is defined as "non-nil means ignore case
when searching"; various search and replace functions refer to it
directly or through their subroutines, but do not bind or set it.
Then you can bind the variable in other programs, knowing reliably what
the effect will be.
In either case, you should define the variable with defvar.
This helps other people understand your program by telling them to look
for inter-function usage. It also avoids a warning from the byte
compiler. Choose the variable's name to avoid name conflicts--don't
use short names like x.
Global and local variable bindings are found in most programming languages in one form or another. Emacs also supports additional, unusual kinds of variable binding: buffer-local bindings, which apply only in one buffer, and frame-local bindings, which apply only in one frame. Having different values for a variable in different buffers and/or frames is an important customization method.
This section describes buffer-local bindings; for frame-local bindings, see the following section, section Frame-Local Variables. (A few variables have bindings that are local to each terminal; see section Multiple Displays.)
A buffer-local variable has a buffer-local binding associated with a particular buffer. The binding is in effect when that buffer is current; otherwise, it is not in effect. If you set the variable while a buffer-local binding is in effect, the new value goes in that binding, so its other bindings are unchanged. This means that the change is visible only in the buffer where you made it.
The variable's ordinary binding, which is not associated with any specific buffer, is called the default binding. In most cases, this is the global binding.
A variable can have buffer-local bindings in some buffers but not in other buffers. The default binding is shared by all the buffers that don't have their own bindings for the variable. (This includes all newly created buffers.) If you set the variable in a buffer that does not have a buffer-local binding for it, this sets the default binding (assuming there are no frame-local bindings to complicate the matter), so the new value is visible in all the buffers that see the default binding.
The most common use of buffer-local bindings is for major modes to change
variables that control the behavior of commands. For example, C mode and
Lisp mode both set the variable paragraph-start to specify that only
blank lines separate paragraphs. They do this by making the variable
buffer-local in the buffer that is being put into C mode or Lisp mode, and
then setting it to the new value for that mode. See section Major Modes.
The usual way to make a buffer-local binding is with
make-local-variable, which is what major mode commands typically
use. This affects just the current buffer; all other buffers (including
those yet to be created) will continue to share the default value unless
they are explicitly given their own buffer-local bindings.
A more powerful operation is to mark the variable as
automatically buffer-local by calling
make-variable-buffer-local. You can think of this as making the
variable local in all buffers, even those yet to be created. More
precisely, the effect is that setting the variable automatically makes
the variable local to the current buffer if it is not already so. All
buffers start out by sharing the default value of the variable as usual,
but setting the variable creates a buffer-local binding for the current
buffer. The new value is stored in the buffer-local binding, leaving
the default binding untouched. This means that the default value cannot
be changed with setq in any buffer; the only way to change it is
with setq-default.
Warning: When a variable has buffer-local values in one or
more buffers, you can get Emacs very confused by binding the variable
with let, changing to a different current buffer in which a
different binding is in effect, and then exiting the let. This
can scramble the values of the buffer-local and default bindings.
To preserve your sanity, avoid using a variable in that way. If you
use save-excursion around each piece of code that changes to a
different current buffer, you will not have this problem
(see section Excursions). Here is an example of what to avoid:
(setq foo 'b)
(set-buffer "a")
(make-local-variable 'foo)
(setq foo 'a)
(let ((foo 'temp))
(set-buffer "b")
body...)
foo => 'a ; The old buffer-local value from buffer `a'
; is now the default value.
(set-buffer "a")
foo => 'temp ; The local let value that should be gone
; is now the buffer-local value in buffer `a'.
But save-excursion as shown here avoids the problem:
(let ((foo 'temp))
(save-excursion
(set-buffer "b")
body...))
Note that references to foo in body access the
buffer-local binding of buffer `b'.
When a file specifies local variable values, these become buffer-local values when you visit the file. See section `File Variables' in The GNU Emacs Manual.
The buffer-local value of variable starts out as the same value variable previously had. If variable was void, it remains void.
;; In buffer `b1':
(setq foo 5) ; Affects all buffers.
=> 5
(make-local-variable 'foo) ; Now it is local in `b1'.
=> foo
foo ; That did not change
=> 5 ; the value.
(setq foo 6) ; Change the value
=> 6 ; in `b1'.
foo
=> 6
;; In buffer `b2', the value hasn't changed.
(save-excursion
(set-buffer "b2")
foo)
=> 5
Making a variable buffer-local within a let-binding for that
variable does not work reliably, unless the buffer in which you do this
is not current either on entry to or exit from the let. This is
because let does not distinguish between different kinds of
bindings; it knows only which variable the binding was made for.
If the variable is terminal-local, this function signals an error. Such variables cannot have buffer-local bindings as well. See section Multiple Displays.
Note: do not use make-local-variable for a hook
variable. Instead, use make-local-hook. See section Hooks.
A peculiar wrinkle of this feature is that binding the variable (with
let or other binding constructs) does not create a buffer-local
binding for it. Only setting the variable (with set or
setq) does so.
The value returned is variable.
Warning: Don't assume that you should use
make-variable-buffer-local for user-option variables, simply
because users might want to customize them differently in
different buffers. Users can make any variable local, when they wish
to. It is better to leave the choice to them.
The time to use make-variable-buffer-local is when it is crucial
that no two buffers ever share the same binding. For example, when a
variable is used for internal purposes in a Lisp program which depends
on having separate values in separate buffers, then using
make-variable-buffer-local can be the best solution.
t if variable is buffer-local in buffer
buffer (which defaults to the current buffer); otherwise,
nil.
(make-local-variable 'foobar)
(makunbound 'foobar)
(make-local-variable 'bind-me)
(setq bind-me 69)
(setq lcl (buffer-local-variables))
;; First, built-in variables local in all buffers:
=> ((mark-active . nil)
(buffer-undo-list . nil)
(mode-name . "Fundamental")
...
;; Next, non-built-in buffer-local variables.
;; This one is buffer-local and void:
foobar
;; This one is buffer-local and nonvoid:
(bind-me . 69))
Note that storing new values into the CDRs of cons cells in this list does not change the buffer-local values of the variables.
If you kill the buffer-local binding of a variable that automatically becomes buffer-local when set, this makes the default value visible in the current buffer. However, if you set the variable again, that will once again create a buffer-local binding for it.
kill-local-variable returns variable.
This function is a command because it is sometimes useful to kill one buffer-local variable interactively, just as it is useful to create buffer-local variables interactively.
This function also resets certain other information pertaining to the
buffer: it sets the local keymap to nil, the syntax table to the
value of (standard-syntax-table), the case table to
(standard-case-table), and the abbrev table to the value of
fundamental-mode-abbrev-table.
The very first thing this function does is run the normal hook
change-major-mode-hook (see below).
Every major mode command begins by calling this function, which has the effect of switching to Fundamental mode and erasing most of the effects of the previous major mode. To ensure that this does its job, the variables that major modes set should not be marked permanent.
kill-all-local-variables returns nil.
kill-all-local-variables runs this normal hook
before it does anything else. This gives major modes a way to arrange
for something special to be done if the user switches to a different
major mode. For best results, make this variable buffer-local, so that
it will disappear after doing its job and will not interfere with the
subsequent major mode. See section Hooks.
A buffer-local variable is permanent if the variable name (a
symbol) has a permanent-local property that is non-nil.
Permanent locals are appropriate for data pertaining to where the file
came from or how to save it, rather than with how to edit the contents.
The global value of a variable with buffer-local bindings is also called the default value, because it is the value that is in effect whenever neither the current buffer nor the selected frame has its own binding for the variable.
The functions default-value and setq-default access and
change a variable's default value regardless of whether the current
buffer has a buffer-local binding. For example, you could use
setq-default to change the default setting of
paragraph-start for most buffers; and this would work even when
you are in a C or Lisp mode buffer that has a buffer-local value for
this variable.
The special forms defvar and defconst also set the
default value (if they set the variable at all), rather than any
buffer-local or frame-local value.
symbol-value (see section Accessing Variable Values).
default-boundp tells you whether symbol's
default value is nonvoid. If (default-boundp 'foo) returns
nil, then (default-value 'foo) would get an error.
default-boundp is to default-value as boundp is to
symbol-value.
setq-default form is the value of the last form.
If a symbol is not buffer-local for the current buffer, and is not
marked automatically buffer-local, setq-default has the same
effect as setq. If symbol is buffer-local for the current
buffer, then this changes the value that other buffers will see (as long
as they don't have a buffer-local value), but not the value that the
current buffer sees.
;; In buffer `foo':
(make-local-variable 'buffer-local)
=> buffer-local
(setq buffer-local 'value-in-foo)
=> value-in-foo
(setq-default buffer-local 'new-default)
=> new-default
buffer-local
=> value-in-foo
(default-value 'buffer-local)
=> new-default
;; In (the new) buffer `bar':
buffer-local
=> new-default
(default-value 'buffer-local)
=> new-default
(setq buffer-local 'another-default)
=> another-default
(default-value 'buffer-local)
=> another-default
;; Back in buffer `foo':
buffer-local
=> value-in-foo
(default-value 'buffer-local)
=> another-default
setq-default, except that symbol is
an ordinary evaluated argument.
(set-default (car '(a b c)) 23)
=> 23
(default-value 'a)
=> 23
Just as variables can have buffer-local bindings, they can also have
frame-local bindings. These bindings belong to one frame, and are in
effect when that frame is selected. Frame-local bindings are actually
frame parameters: you create a frame-local binding in a specific frame
by calling modify-frame-parameters and specifying the variable
name as the parameter name.
To enable frame-local bindings for a certain variable, call the function
make-variable-frame-local.
If the variable is terminal-local, this function signals an error, because such variables cannot have frame-local bindings as well. See section Multiple Displays. A few variables that are implemented specially in Emacs can be (and usually are) buffer-local, but can never be frame-local.
Buffer-local bindings take precedence over frame-local bindings. Thus,
consider a variable foo: if the current buffer has a buffer-local
binding for foo, that binding is active; otherwise, if the
selected frame has a frame-local binding for foo, that binding is
active; otherwise, the default binding of foo is active.
Here is an example. First we prepare a few bindings for foo:
(setq f1 (selected-frame)) (make-variable-frame-local 'foo) ;; Make a buffer-local binding forfooin `b1'. (set-buffer (get-buffer-create "b1")) (make-local-variable 'foo) (setq foo '(b 1)) ;; Make a frame-local binding forfooin a new frame. ;; Store that frame inf2. (setq f2 (make-frame)) (modify-frame-parameters f2 '((foo . (f 2))))
Now we examine foo in various contexts. Whenever the
buffer `b1' is current, its buffer-local binding is in effect,
regardless of the selected frame:
(select-frame f1)
(set-buffer (get-buffer-create "b1"))
foo
=> (b 1)
(select-frame f2)
(set-buffer (get-buffer-create "b1"))
foo
=> (b 1)
Otherwise, the frame gets a chance to provide the binding; when frame
f2 is selected, its frame-local binding is in effect:
(select-frame f2)
(set-buffer (get-buffer "*scratch*"))
foo
=> (f 2)
When neither the current buffer nor the selected frame provides a binding, the default binding is used:
(select-frame f1)
(set-buffer (get-buffer "*scratch*"))
foo
=> nil
When the active binding of a variable is a frame-local binding, setting
the variable changes that binding. You can observe the result with
frame-parameters:
(select-frame f2)
(set-buffer (get-buffer "*scratch*"))
(setq foo 'nobody)
(assq 'foo (frame-parameters f2))
=> (foo . nobody)
We have considered the idea of bindings that are local to a category
of frames--for example, all color frames, or all frames with dark
backgrounds. We have not implemented them because it is not clear that
this feature is really useful. You can get more or less the same
results by adding a function to after-make-frame-hook, set up to
define a particular frame parameter according to the appropriate
conditions for each frame.
It would also be possible to implement window-local bindings. We don't know of many situations where they would be useful, and it seems that indirect buffers (see section Indirect Buffers) with buffer-local bindings offer a way to handle these situations more robustly.
If sufficient application is found for either of these two kinds of local bindings, we will provide it in a subsequent Emacs version.
A Lisp program is composed mainly of Lisp functions. This chapter explains what functions are, how they accept arguments, and how to define them.
In a general sense, a function is a rule for carrying on a computation given several values called arguments. The result of the computation is called the value of the function. The computation can also have side effects: lasting changes in the values of variables or the contents of data structures.
Here are important terms for functions in Emacs Lisp and for other function-like objects.
car or append. These functions are also called
built-in functions or subrs. (Special forms are also
considered primitives.)
Usually the reason we implement a function as a primitive is either
because it is fundamental, because it provides a low-level interface to
operating system services, or because it needs to run fast. Primitives
can be modified or added only by changing the C sources and recompiling
the editor. See section Writing Emacs Primitives.
command-execute can invoke; it
is a possible definition for a key sequence. Some functions are
commands; a function written in Lisp is a command if it contains an
interactive declaration (see section Defining Commands). Such a function
can be called from Lisp expressions like other functions; in this case,
the fact that the function is a command makes no difference.
Keyboard macros (strings and vectors) are commands also, even though
they are not functions. A symbol is a command if its function
definition is a command; such symbols can be invoked with M-x.
The symbol is a function as well if the definition is a function.
See section Command Loop Overview.
t if object is any kind of function,
or a special form or macro.
t if object is a built-in function
(i.e., a Lisp primitive).
(subrp 'message) ; message is a symbol,
=> nil ; not a subr object.
(subrp (symbol-function 'message))
=> t
t if object is a byte-code
function. For example:
(byte-code-function-p (symbol-function 'next-line))
=> t
A function written in Lisp is a list that looks like this:
(lambda (arg-variables...) [documentation-string] [interactive-declaration] body-forms...)
Such a list is called a lambda expression. In Emacs Lisp, it actually is valid as an expression--it evaluates to itself. In some other Lisp dialects, a lambda expression is not a valid expression at all. In either case, its main use is not to be evaluated as an expression, but to be called as a function.
The first element of a lambda expression is always the symbol
lambda. This indicates that the list represents a function. The
reason functions are defined to start with lambda is so that
other lists, intended for other uses, will not accidentally be valid as
functions.
The second element is a list of symbols--the argument variable names. This is called the lambda list. When a Lisp function is called, the argument values are matched up against the variables in the lambda list, which are given local bindings with the values provided. See section Local Variables.
The documentation string is a Lisp string object placed within the function definition to describe the function for the Emacs help facilities. See section Documentation Strings of Functions.
The interactive declaration is a list of the form (interactive
code-string). This declares how to provide arguments if the
function is used interactively. Functions with this declaration are called
commands; they can be called using M-x or bound to a key.
Functions not intended to be called in this way should not have interactive
declarations. See section Defining Commands, for how to write an interactive
declaration.
The rest of the elements are the body of the function: the Lisp code to do the work of the function (or, as a Lisp programmer would say, "a list of Lisp forms to evaluate"). The value returned by the function is the value returned by the last element of the body.
Consider for example the following function:
(lambda (a b c) (+ a b c))
We can call this function by writing it as the CAR of an expression, like this:
((lambda (a b c) (+ a b c)) 1 2 3)
This call evaluates the body of the lambda expression with the variable
a bound to 1, b bound to 2, and c bound to 3.
Evaluation of the body adds these three numbers, producing the result 6;
therefore, this call to the function returns the value 6.
Note that the arguments can be the results of other function calls, as in this example:
((lambda (a b c) (+ a b c)) 1 (* 2 3) (- 5 4))
This evaluates the arguments 1, (* 2 3), and (- 5
4) from left to right. Then it applies the lambda expression to the
argument values 1, 6 and 1 to produce the value 8.
It is not often useful to write a lambda expression as the CAR of
a form in this way. You can get the same result, of making local
variables and giving them values, using the special form let
(see section Local Variables). And let is clearer and easier to use.
In practice, lambda expressions are either stored as the function
definitions of symbols, to produce named functions, or passed as
arguments to other functions (see section Anonymous Functions).
However, calls to explicit lambda expressions were very useful in the
old days of Lisp, before the special form let was invented. At
that time, they were the only way to bind and initialize local
variables.
Our simple sample function, (lambda (a b c) (+ a b c)),
specifies three argument variables, so it must be called with three
arguments: if you try to call it with only two arguments or four
arguments, you get a wrong-number-of-arguments error.
It is often convenient to write a function that allows certain
arguments to be omitted. For example, the function substring
accepts three arguments--a string, the start index and the end
index--but the third argument defaults to the length of the
string if you omit it. It is also convenient for certain functions to
accept an indefinite number of arguments, as the functions list
and + do.
To specify optional arguments that may be omitted when a function
is called, simply include the keyword &optional before the optional
arguments. To specify a list of zero or more extra arguments, include the
keyword &rest before one final argument.
Thus, the complete syntax for an argument list is as follows:
(required-vars... [&optional optional-vars...] [&rest rest-var])
The square brackets indicate that the &optional and &rest
clauses, and the variables that follow them, are optional.
A call to the function requires one actual argument for each of the
required-vars. There may be actual arguments for zero or more of
the optional-vars, and there cannot be any actual arguments beyond
that unless the lambda list uses &rest. In that case, there may
be any number of extra actual arguments.
If actual arguments for the optional and rest variables are omitted,
then they always default to nil. There is no way for the
function to distinguish between an explicit argument of nil and
an omitted argument. However, the body of the function is free to
consider nil an abbreviation for some other meaningful value.
This is what substring does; nil as the third argument to
substring means to use the length of the string supplied.
Common Lisp note: Common Lisp allows the function to specify what default value to use when an optional argument is omitted; Emacs Lisp always uses
nil. Emacs Lisp does not support "supplied-p" variables that tell you whether an argument was explicitly passed.
For example, an argument list that looks like this:
(a b &optional c d &rest e)
binds a and b to the first two actual arguments, which are
required. If one or two more arguments are provided, c and
d are bound to them respectively; any arguments after the first
four are collected into a list and e is bound to that list. If
there are only two arguments, c is nil; if two or three
arguments, d is nil; if four arguments or fewer, e
is nil.
There is no way to have required arguments following optional
ones--it would not make sense. To see why this must be so, suppose
that c in the example were optional and d were required.
Suppose three actual arguments are given; which variable would the third
argument be for? Similarly, it makes no sense to have any more
arguments (either required or optional) after a &rest argument.
Here are some examples of argument lists and proper calls:
((lambda (n) (1+ n)) ; One required:
1) ; requires exactly one argument.
=> 2
((lambda (n &optional n1) ; One required and one optional:
(if n1 (+ n n1) (1+ n))) ; 1 or 2 arguments.
1 2)
=> 3
((lambda (n &rest ns) ; One required and one rest:
(+ n (apply '+ ns))) ; 1 or more arguments.
1 2 3 4 5)
=> 15
A lambda expression may optionally have a documentation string just after the lambda list. This string does not affect execution of the function; it is a kind of comment, but a systematized comment which actually appears inside the Lisp world and can be used by the Emacs help facilities. See section Documentation, for how the documentation-string is accessed.
It is a good idea to provide documentation strings for all the functions in your program, even those that are called only from within your program. Documentation strings are like comments, except that they are easier to access.
The first line of the documentation string should stand on its own,
because apropos displays just this first line. It should consist
of one or two complete sentences that summarize the function's purpose.
The start of the documentation string is usually indented in the source file, but since these spaces come before the starting double-quote, they are not part of the string. Some people make a practice of indenting any additional lines of the string so that the text lines up in the program source. This is a mistake. The indentation of the following lines is inside the string; what looks nice in the source code will look ugly when displayed by the help commands.
You may wonder how the documentation string could be optional, since there are required components of the function that follow it (the body). Since evaluation of a string returns that string, without any side effects, it has no effect if it is not the last form in the body. Thus, in practice, there is no confusion between the first form of the body and the documentation string; if the only body form is a string then it serves both as the return value and as the documentation.
In most computer languages, every function has a name; the idea of a
function without a name is nonsensical. In Lisp, a function in the
strictest sense has no name. It is simply a list whose first element is
lambda, a byte-code function object, or a primitive subr-object.
However, a symbol can serve as the name of a function. This happens when you put the function in the symbol's function cell (see section Symbol Components). Then the symbol itself becomes a valid, callable function, equivalent to the list or subr-object that its function cell refers to. The contents of the function cell are also called the symbol's function definition. The procedure of using a symbol's function definition in place of the symbol is called symbol function indirection; see section Symbol Function Indirection.
In practice, nearly all functions are given names in this way and
referred to through their names. For example, the symbol car works
as a function and does what it does because the primitive subr-object
#<subr car> is stored in its function cell.
We give functions names because it is convenient to refer to them by
their names in Lisp expressions. For primitive subr-objects such as
#<subr car>, names are the only way you can refer to them: there
is no read syntax for such objects. For functions written in Lisp, the
name is more convenient to use in a call than an explicit lambda
expression. Also, a function with a name can refer to itself--it can
be recursive. Writing the function's name in its own definition is much
more convenient than making the function definition point to itself
(something that is not impossible but that has various disadvantages in
practice).
We often identify functions with the symbols used to name them. For
example, we often speak of "the function car", not
distinguishing between the symbol car and the primitive
subr-object that is its function definition. For most purposes, there
is no need to distinguish.
Even so, keep in mind that a function need not have a unique name. While
a given function object usually appears in the function cell of only
one symbol, this is just a matter of convenience. It is easy to store
it in several symbols using fset; then each of the symbols is
equally well a name for the same function.
A symbol used as a function name may also be used as a variable; these two uses of a symbol are independent and do not conflict. (Some Lisp dialects, such as Scheme, do not distinguish between a symbol's value and its function definition; a symbol's value as a variable is also its function definition.) If you have not given a symbol a function definition, you cannot use it as a function; whether the symbol has a value as a variable makes no difference to this.
We usually give a name to a function when it is first created. This
is called defining a function, and it is done with the
defun special form.
defun is the usual way to define new Lisp functions. It
defines the symbol name as a function that looks like this:
(lambda argument-list . body-forms)
defun stores this lambda expression in the function cell of
name. It returns the value name, but usually we ignore this
value.
As described previously (see section Lambda Expressions),
argument-list is a list of argument names and may include the
keywords &optional and &rest. Also, the first two of the
body-forms may be a documentation string and an interactive
declaration.
There is no conflict if the same symbol name is also used as a variable, since the symbol's value cell is independent of the function cell. See section Symbol Components.
Here are some examples:
(defun foo () 5)
=> foo
(foo)
=> 5
(defun bar (a &optional b &rest c)
(list a b c))
=> bar
(bar 1 2 3 4 5)
=> (1 2 (3 4 5))
(bar 1)
=> (1 nil nil)
(bar)
error--> Wrong number of arguments.
(defun capitalize-backwards ()
"Upcase the last letter of a word."
(interactive)
(backward-word 1)
(forward-word 1)
(backward-char 1)
(capitalize-word 1))
=> capitalize-backwards
Be careful not to redefine existing functions unintentionally.
defun redefines even primitive functions such as car
without any hesitation or notification. Redefining a function already
defined is often done deliberately, and there is no way to distinguish
deliberate redefinition from unintentional redefinition.
The proper place to use defalias is where a specific function
name is being defined--especially where that name appears explicitly in
the source file being loaded. This is because defalias records
which file defined the function, just like defun
(see section Unloading).
By contrast, in programs that manipulate function definitions for other
purposes, it is better to use fset, which does not keep such
records.
See also defsubst, which defines a function like defun
and tells the Lisp compiler to open-code it. See section Inline Functions.
Defining functions is only half the battle. Functions don't do anything until you call them, i.e., tell them to run. Calling a function is also known as invocation.
The most common way of invoking a function is by evaluating a list.
For example, evaluating the list (concat "a" "b") calls the
function concat with arguments "a" and "b".
See section Evaluation, for a description of evaluation.
When you write a list as an expression in your program, the function
name it calls is written in your program. This means that you choose
which function to call, and how many arguments to give it, when you
write the program. Usually that's just what you want. Occasionally you
need to compute at run time which function to call. To do that, use the
function funcall. When you also need to determine at run time
how many arguments to pass, use apply.
funcall calls function with arguments, and returns
whatever function returns.
Since funcall is a function, all of its arguments, including
function, are evaluated before funcall is called. This
means that you can use any expression to obtain the function to be
called. It also means that funcall does not see the expressions
you write for the arguments, only their values. These values are
not evaluated a second time in the act of calling function;
funcall enters the normal procedure for calling a function at the
place where the arguments have already been evaluated.
The argument function must be either a Lisp function or a
primitive function. Special forms and macros are not allowed, because
they make sense only when given the "unevaluated" argument
expressions. funcall cannot provide these because, as we saw
above, it never knows them in the first place.
(setq f 'list)
=> list
(funcall f 'x 'y 'z)
=> (x y z)
(funcall f 'x 'y '(z))
=> (x y (z))
(funcall 'and t nil)
error--> Invalid function: #<subr and>
Compare these example with the examples of apply.
apply calls function with arguments, just like
funcall but with one difference: the last of arguments is a
list of objects, which are passed to function as separate
arguments, rather than a single list. We say that apply
spreads this list so that each individual element becomes an
argument.
apply returns the result of calling function. As with
funcall, function must either be a Lisp function or a
primitive function; special forms and macros do not make sense in
apply.
(setq f 'list)
=> list
(apply f 'x 'y 'z)
error--> Wrong type argument: listp, z
(apply '+ 1 2 '(3 4))
=> 10
(apply '+ '(1 2 3 4))
=> 10
(apply 'append '((a b c) nil (x y z) nil))
=> (a b c x y z)
For an interesting example of using apply, see the description of
mapcar, in section Mapping Functions.
It is common for Lisp functions to accept functions as arguments or
find them in data structures (especially in hook variables and property
lists) and call them using funcall or apply. Functions
that accept function arguments are often called functionals.
Sometimes, when you call a functional, it is useful to supply a no-op function as the argument. Here are two different kinds of no-op function:
nil.
A mapping function applies a given function to each element of a
list or other collection. Emacs Lisp has several such functions;
mapcar and mapconcat, which scan a list, are described
here. See section Creating and Interning Symbols, for the function mapatoms which
maps over the symbols in an obarray.
These mapping functions do not allow char-tables because a char-table
is a sparse array whose nominal range of indices is very large. To map
over a char-table in a way that deals properly with its sparse nature,
use the function map-char-table (see section Char-Tables).
mapcar applies function to each element of sequence
in turn, and returns a list of the results.
The argument sequence can be any kind of sequence except a char-table; that is, a list, a vector, a bool-vector, or a string. The result is always a list. The length of the result is the same as the length of sequence.
For example:
(mapcar 'car '((a b) (c d) (e f)))
=> (a c e)
(mapcar '1+ [1 2 3])
=> (2 3 4)
(mapcar 'char-to-string "abc")
=> ("a" "b" "c")
;; Call each function in my-hooks.
(mapcar 'funcall my-hooks)
(defun mapcar* (function &rest args)
"Apply FUNCTION to successive cars of all ARGS.
Return the list of results."
;; If no list is exhausted,
(if (not (memq 'nil args))
;; apply function to CARs.
(cons (apply function (mapcar 'car args))
(apply 'mapcar* function
;; Recurse for rest of elements.
(mapcar 'cdr args)))))
(mapcar* 'cons '(a b c) '(1 2 3 4))
=> ((a . 1) (b . 2) (c . 3))
mapconcat applies function to each element of
sequence: the results, which must be strings, are concatenated.
Between each pair of result strings, mapconcat inserts the string
separator. Usually separator contains a space or comma or
other suitable punctuation.
The argument function must be a function that can take one argument and return a string. The argument sequence can be any kind of sequence except a char-table; that is, a list, a vector, a bool-vector, or a string.
(mapconcat 'symbol-name
'(The cat in the hat)
" ")
=> "The cat in the hat"
(mapconcat (function (lambda (x) (format "%c" (1+ x))))
"HAL-8000"
"")
=> "IBM.9111"
In Lisp, a function is a list that starts with lambda, a
byte-code function compiled from such a list, or alternatively a
primitive subr-object; names are "extra". Although usually functions
are defined with defun and given names at the same time, it is
occasionally more concise to use an explicit lambda expression--an
anonymous function. Such a list is valid wherever a function name is.
Any method of creating such a list makes a valid function. Even this:
(setq silly (append '(lambda (x)) (list (list '+ (* 3 4) 'x)))) => (lambda (x) (+ 12 x))
This computes a list that looks like (lambda (x) (+ 12 x)) and
makes it the value (not the function definition!) of
silly.
Here is how we might call this function:
(funcall silly 1) => 13
(It does not work to write (silly 1), because this function
is not the function definition of silly. We have not given
silly any function definition, just a value as a variable.)
Most of the time, anonymous functions are constants that appear in
your program. For example, you might want to pass one as an argument to
the function mapcar, which applies any given function to each
element of a list.
Here we define a function change-property which
uses a function as its third argument:
(defun change-property (symbol prop function)
(let ((value (get symbol prop)))
(put symbol prop (funcall function value))))
Here we define a function that uses change-property,
passing it a function to double a number:
(defun double-property (symbol prop) (change-property symbol prop '(lambda (x) (* 2 x))))
In such cases, we usually use the special form function instead
of simple quotation to quote the anonymous function, like this:
(defun double-property (symbol prop)
(change-property symbol prop
(function (lambda (x) (* 2 x)))))
Using function instead of quote makes a difference if you
compile the function double-property. For example, if you
compile the second definition of double-property, the anonymous
function is compiled as well. By contrast, if you compile the first
definition which uses ordinary quote, the argument passed to
change-property is the precise list shown:
(lambda (x) (* x 2))
The Lisp compiler cannot assume this list is a function, even though it
looks like one, since it does not know what change-property will
do with the list. Perhaps it will check whether the CAR of the third
element is the symbol *! Using function tells the
compiler it is safe to go ahead and compile the constant function.
We sometimes write function instead of quote when
quoting the name of a function, but this usage is just a sort of
comment:
(function symbol) == (quote symbol) == 'symbol
The read syntax #' is a short-hand for using function.
For example,
#'(lambda (x) (* x x))
is equivalent to
(function (lambda (x) (* x x)))
quote. However, it serves as a
note to the Emacs Lisp compiler that function-object is intended
to be used only as a function, and therefore can safely be compiled.
Contrast this with quote, in section Quoting.
See documentation in section Access to Documentation Strings, for a
realistic example using function and an anonymous function.
The function definition of a symbol is the object stored in the function cell of the symbol. The functions described here access, test, and set the function cell of symbols.
See also the function indirect-function in section Symbol Function Indirection.
void-function error is
signaled.
This function does not check that the returned object is a legitimate function.
(defun bar (n) (+ n 2))
=> bar
(symbol-function 'bar)
=> (lambda (n) (+ n 2))
(fset 'baz 'bar)
=> bar
(symbol-function 'baz)
=> bar
If you have never given a symbol any function definition, we say that
that symbol's function cell is void. In other words, the function
cell does not have any Lisp object in it. If you try to call such a symbol
as a function, it signals a void-function error.
Note that void is not the same as nil or the symbol
void. The symbols nil and void are Lisp objects,
and can be stored into a function cell just as any other object can be
(and they can be valid functions if you define them in turn with
defun). A void function cell contains no object whatsoever.
You can test the voidness of a symbol's function definition with
fboundp. After you have given a symbol a function definition, you
can make it void once more using fmakunbound.
t if the symbol has an object in its
function cell, nil otherwise. It does not check that the object
is a legitimate function.
void-function
error. (See also makunbound, in section When a Variable is "Void".)
(defun foo (x) x)
=> foo
(foo 1)
=>1
(fmakunbound 'foo)
=> foo
(foo 1)
error--> Symbol's function definition is void: foo
There are three normal uses of this function:
defalias instead of
fset; see section Defining Functions.)
defun. For example, you can use fset
to give a symbol s1 a function definition which is another symbol
s2; then s1 serves as an alias for whatever definition
s2 presently has. (Once again use defalias instead of
fset if you think of this as the definition of s1.)
defun
were not a primitive, it could be written in Lisp (as a macro) using
fset.
Here are examples of these uses:
;; Savefoo's definition inold-foo. (fset 'old-foo (symbol-function 'foo)) ;; Make the symbolcarthe function definition ofxfirst. ;; (Most likely,defaliaswould be better thanfsethere.) (fset 'xfirst 'car) => car (xfirst '(1 2 3)) => 1 (symbol-function 'xfirst) => car (symbol-function (symbol-function 'xfirst)) => #<subr car> ;; Define a named keyboard macro. (fset 'kill-two-lines "\^u2\^k") => "\^u2\^k" ;; Here is a function that alters other functions. (defun copy-function-definition (new old) "Define NEW with the same function definition as OLD." (fset new (symbol-function old)))
When writing a function that extends a previously defined function, the following idiom is sometimes used:
(fset 'old-foo (symbol-function 'foo)) (defun foo () "Just like old-foo, except more so." (old-foo) (more-so))
This does not work properly if foo has been defined to autoload.
In such a case, when foo calls old-foo, Lisp attempts
to define old-foo by loading a file. Since this presumably
defines foo rather than old-foo, it does not produce the
proper results. The only way to avoid this problem is to make sure the
file is loaded before moving aside the old definition of foo.
But it is unmodular and unclean, in any case, for a Lisp file to redefine a function defined elsewhere. It is cleaner to use the advice facility (see section Advising Emacs Lisp Functions).
You can define an inline function by using defsubst instead
of defun. An inline function works just like an ordinary
function except for one thing: when you compile a call to the function,
the function's definition is open-coded into the caller.
Making a function inline makes explicit calls run faster. But it also has disadvantages. For one thing, it reduces flexibility; if you change the definition of the function, calls already inlined still use the old definition until you recompile them. Since the flexibility of redefining functions is an important feature of Emacs, you should not make a function inline unless its speed is really crucial.
Another disadvantage is that making a large function inline can increase the size of compiled code both in files and in memory. Since the speed advantage of inline functions is greatest for small functions, you generally should not make large functions inline.
It's possible to define a macro to expand into the same code that an
inline function would execute. (See section Macros.) But the macro would be
limited to direct use in expressions--a macro cannot be called with
apply, mapcar and so on. Also, it takes some work to
convert an ordinary function into a macro. To convert it into an inline
function is very easy; simply replace defun with defsubst.
Since each argument of an inline function is evaluated exactly once, you
needn't worry about how many times the body uses the arguments, as you
do for macros. (See section Evaluating Macro Arguments Repeatedly.)
Inline functions can be used and open-coded later on in the same file, following the definition, just like macros.
Here is a table of several functions that do things related to function calling and function definitions. They are documented elsewhere, but we provide cross references here.
apply
autoload
call-interactively
commandp
documentation
eval
funcall
function
ignore
indirect-function
interactive
interactive.
interactive-p
mapatoms
mapcar
map-char-table
mapconcat
undefined
Macros enable you to define new control constructs and other language features. A macro is defined much like a function, but instead of telling how to compute a value, it tells how to compute another Lisp expression which will in turn compute the value. We call this expression the expansion of the macro.
Macros can do this because they operate on the unevaluated expressions for the arguments, not on the argument values as functions do. They can therefore construct an expansion containing these argument expressions or parts of them.
If you are using a macro to do something an ordinary function could do, just for the sake of speed, consider using an inline function instead. See section Inline Functions.
Suppose we would like to define a Lisp construct to increment a
variable value, much like the ++ operator in C. We would like to
write (inc x) and have the effect of (setq x (1+ x)).
Here's a macro definition that does the job:
(defmacro inc (var) (list 'setq var (list '1+ var)))
When this is called with (inc x), the argument var is the
symbol x---not the value of x, as it would
be in a function. The body of the macro uses this to construct the
expansion, which is (setq x (1+ x)). Once the macro definition
returns this expansion, Lisp proceeds to evaluate it, thus incrementing
x.
A macro call looks just like a function call in that it is a list which starts with the name of the macro. The rest of the elements of the list are the arguments of the macro.
Evaluation of the macro call begins like evaluation of a function call except for one crucial difference: the macro arguments are the actual expressions appearing in the macro call. They are not evaluated before they are given to the macro definition. By contrast, the arguments of a function are results of evaluating the elements of the function call list.
Having obtained the arguments, Lisp invokes the macro definition just
as a function is invoked. The argument variables of the macro are bound
to the argument values from the macro call, or to a list of them in the
case of a &rest argument. And the macro body executes and
returns its value just as a function body does.
The second crucial difference between macros and functions is that the value returned by the macro body is not the value of the macro call. Instead, it is an alternate expression for computing that value, also known as the expansion of the macro. The Lisp interpreter proceeds to evaluate the expansion as soon as it comes back from the macro.
Since the expansion is evaluated in the normal manner, it may contain calls to other macros. It may even be a call to the same macro, though this is unusual.
You can see the expansion of a given macro call by calling
macroexpand.
macroexpand. If form is not a macro call to begin with, it
is returned as given.
Note that macroexpand does not look at the subexpressions of
form (although some macro definitions may do so). Even if they
are macro calls themselves, macroexpand does not expand them.
The function macroexpand does not expand calls to inline functions.
Normally there is no need for that, since a call to an inline function is
no harder to understand than a call to an ordinary function.
If environment is provided, it specifies an alist of macro definitions that shadow the currently defined macros. Byte compilation uses this feature.
(defmacro inc (var)
(list 'setq var (list '1+ var)))
=> inc
(macroexpand '(inc r))
=> (setq r (1+ r))
(defmacro inc2 (var1 var2)
(list 'progn (list 'inc var1) (list 'inc var2)))
=> inc2
(macroexpand '(inc2 r s))
=> (progn (inc r) (inc s)) ; inc not expanded here.
You might ask why we take the trouble to compute an expansion for a macro and then evaluate the expansion. Why not have the macro body produce the desired results directly? The reason has to do with compilation.
When a macro call appears in a Lisp program being compiled, the Lisp compiler calls the macro definition just as the interpreter would, and receives an expansion. But instead of evaluating this expansion, it compiles the expansion as if it had appeared directly in the program. As a result, the compiled code produces the value and side effects intended for the macro, but executes at full compiled speed. This would not work if the macro body computed the value and side effects itself--they would be computed at compile time, which is not useful.
In order for compilation of macro calls to work, the macros must
already be defined in Lisp when the calls to them are compiled. The
compiler has a special feature to help you do this: if a file being
compiled contains a defmacro form, the macro is defined
temporarily for the rest of the compilation of that file. To make this
feature work, you must put the defmacro in the same file where it
is used, and before its first use.
Byte-compiling a file executes any require calls at top-level
in the file. This is in case the file needs the required packages for
proper compilation. One way to ensure that necessary macro definitions
are available during compilation is to require the files that define
them (see section Features). To avoid loading the macro definition files
when someone runs the compiled program, write
eval-when-compile around the require calls (see section Evaluation During Compilation).
A Lisp macro is a list whose CAR is macro. Its CDR should
be a function; expansion of the macro works by applying the function
(with apply) to the list of unevaluated argument-expressions
from the macro call.
It is possible to use an anonymous Lisp macro just like an anonymous
function, but this is never done, because it does not make sense to pass
an anonymous macro to functionals such as mapcar. In practice,
all Lisp macros have names, and they are usually defined with the
special form defmacro.
defmacro defines the symbol name as a macro that looks
like this:
(macro lambda argument-list . body-forms)
(Note that the CDR of this list is a function--a lambda expression.)
This macro object is stored in the function cell of name. The
value returned by evaluating the defmacro form is name, but
usually we ignore this value.
The shape and meaning of argument-list is the same as in a
function, and the keywords &rest and &optional may be used
(see section Other Features of Argument Lists). Macros may have a documentation string, but
any interactive declaration is ignored since macros cannot be
called interactively.
Macros often need to construct large list structures from a mixture of constants and nonconstant parts. To make this easier, use the ``' syntax (usually called backquote).
Backquote allows you to quote a list, but selectively evaluate
elements of that list. In the simplest case, it is identical to the
special form quote (see section Quoting). For example, these
two forms yield identical results:
`(a list of (+ 2 3) elements)
=> (a list of (+ 2 3) elements)
'(a list of (+ 2 3) elements)
=> (a list of (+ 2 3) elements)
The special marker `,' inside of the argument to backquote indicates a value that isn't constant. Backquote evaluates the argument of `,' and puts the value in the list structure:
(list 'a 'list 'of (+ 2 3) 'elements)
=> (a list of 5 elements)
`(a list of ,(+ 2 3) elements)
=> (a list of 5 elements)
Substitution with `,' is allowed at deeper levels of the list structure also. For example:
(defmacro t-becomes-nil (variable)
`(if (eq ,variable t)
(setq ,variable nil)))
(t-becomes-nil foo)
== (if (eq foo t) (setq foo nil))
You can also splice an evaluated value into the resulting list, using the special marker `,@'. The elements of the spliced list become elements at the same level as the other elements of the resulting list. The equivalent code without using ``' is often unreadable. Here are some examples:
(setq some-list '(2 3))
=> (2 3)
(cons 1 (append some-list '(4) some-list))
=> (1 2 3 4 2 3)
`(1 ,@some-list 4 ,@some-list)
=> (1 2 3 4 2 3)
(setq list '(hack foo bar))
=> (hack foo bar)
(cons 'use
(cons 'the
(cons 'words (append (cdr list) '(as elements)))))
=> (use the words foo bar as elements)
`(use the words ,@(cdr list) as elements)
=> (use the words foo bar as elements)
In old Emacs versions, before version 19.29, ``' used a different syntax which required an extra level of parentheses around the entire backquote construct. Likewise, each `,' or `,@' substitution required an extra level of parentheses surrounding both the `,' or `,@' and the following expression. The old syntax required whitespace between the ``', `,' or `,@' and the following expression.
This syntax is still accepted, for compatibility with old Emacs versions, but we recommend not using it in new programs.
The basic facts of macro expansion have counterintuitive consequences. This section describes some important consequences that can lead to trouble, and rules to follow to avoid trouble.
When defining a macro you must pay attention to the number of times the arguments will be evaluated when the expansion is executed. The following macro (used to facilitate iteration) illustrates the problem. This macro allows us to write a simple "for" loop such as one might find in Pascal.
(defmacro for (var from init to final do &rest body)
"Execute a simple \"for\" loop.
For example, (for i from 1 to 10 do (print i))."
(list 'let (list (list var init))
(cons 'while (cons (list '<= var final)
(append body (list (list 'inc var)))))))
=> for
(for i from 1 to 3 do
(setq square (* i i))
(princ (format "\n%d %d" i square)))
==>
(let ((i 1))
(while (<= i 3)
(setq square (* i i))
(princ (format "%d %d" i square))
(inc i)))
-|1 1
-|2 4
-|3 9
=> nil
The arguments from, to, and do in this macro are
"syntactic sugar"; they are entirely ignored. The idea is that you
will write noise words (such as from, to, and do)
in those positions in the macro call.
Here's an equivalent definition simplified through use of backquote:
(defmacro for (var from init to final do &rest body)
"Execute a simple \"for\" loop.
For example, (for i from 1 to 10 do (print i))."
`(let ((,var ,init))
(while (<= ,var ,final)
,@body
(inc ,var))))
Both forms of this definition (with backquote and without) suffer from
the defect that final is evaluated on every iteration. If
final is a constant, this is not a problem. If it is a more
complex form, say (long-complex-calculation x), this can slow
down the execution significantly. If final has side effects,
executing it more than once is probably incorrect.
A well-designed macro definition takes steps to avoid this problem by
producing an expansion that evaluates the argument expressions exactly
once unless repeated evaluation is part of the intended purpose of the
macro. Here is a correct expansion for the for macro:
(let ((i 1)
(max 3))
(while (<= i max)
(setq square (* i i))
(princ (format "%d %d" i square))
(inc i)))
Here is a macro definition that creates this expansion:
(defmacro for (var from init to final do &rest body)
"Execute a simple for loop: (for i from 1 to 10 do (print i))."
`(let ((,var ,init)
(max ,final))
(while (<= ,var max)
,@body
(inc ,var))))
Unfortunately, this fix introduces another problem, described in the following section.
The new definition of for has a new problem: it introduces a
local variable named max which the user does not expect. This
causes trouble in examples such as the following:
(let ((max 0))
(for x from 0 to 10 do
(let ((this (frob x)))
(if (< max this)
(setq max this)))))
The references to max inside the body of the for, which
are supposed to refer to the user's binding of max, really access
the binding made by for.
The way to correct this is to use an uninterned symbol instead of
max (see section Creating and Interning Symbols). The uninterned symbol can be
bound and referred to just like any other symbol, but since it is
created by for, we know that it cannot already appear in the
user's program. Since it is not interned, there is no way the user can
put it into the program later. It will never appear anywhere except
where put by for. Here is a definition of for that works
this way:
(defmacro for (var from init to final do &rest body)
"Execute a simple for loop: (for i from 1 to 10 do (print i))."
(let ((tempvar (make-symbol "max")))
`(let ((,var ,init)
(,tempvar ,final))
(while (<= ,var ,tempvar)
,@body
(inc ,var)))))
This creates an uninterned symbol named max and puts it in the
expansion instead of the usual interned symbol max that appears
in expressions ordinarily.
Another problem can happen if the macro definition itself
evaluates any of the macro argument expressions, such as by calling
eval (see section Eval). If the argument is supposed to refer to the
user's variables, you may have trouble if the user happens to use a
variable with the same name as one of the macro arguments. Inside the
macro body, the macro argument binding is the most local binding of this
variable, so any references inside the form being evaluated do refer to
it. Here is an example:
(defmacro foo (a)
(list 'setq (eval a) t))
=> foo
(setq x 'b)
(foo x) ==> (setq b t)
=> t ; and b has been set.
;; but
(setq a 'c)
(foo a) ==> (setq a t)
=> t ; but this set a, not c.
It makes a difference whether the user's variable is named a or
x, because a conflicts with the macro argument variable
a.
Another problem with calling eval in a macro definition is that
it probably won't do what you intend in a compiled program. The
byte-compiler runs macro definitions while compiling the program, when
the program's own computations (which you might have wished to access
with eval) don't occur and its local variable bindings don't
exist.
To avoid these problems, don't evaluate an argument expression while computing the macro expansion. Instead, substitute the expression into the macro expansion, so that its value will be computed as part of executing the expansion. This is how the other examples in this chapter work.
Occasionally problems result from the fact that a macro call is expanded each time it is evaluated in an interpreted function, but is expanded only once (during compilation) for a compiled function. If the macro definition has side effects, they will work differently depending on how many times the macro is expanded.
Therefore, you should avoid side effects in computation of the macro expansion, unless you really know what you are doing.
One special kind of side effect can't be avoided: constructing Lisp objects. Almost all macro expansions include constructed lists; that is the whole point of most macros. This is usually safe; there is just one case where you must be careful: when the object you construct is part of a quoted constant in the macro expansion.
If the macro is expanded just once, in compilation, then the object is constructed just once, during compilation. But in interpreted execution, the macro is expanded each time the macro call runs, and this means a new object is constructed each time.
In most clean Lisp code, this difference won't matter. It can matter only if you perform side-effects on the objects constructed by the macro definition. Thus, to avoid trouble, avoid side effects on objects constructed by macro definitions. Here is an example of how such side effects can get you into trouble:
(defmacro empty-object ()
(list 'quote (cons nil nil)))
(defun initialize (condition)
(let ((object (empty-object)))
(if condition
(setcar object condition))
object))
If initialize is interpreted, a new list (nil) is
constructed each time initialize is called. Thus, no side effect
survives between calls. If initialize is compiled, then the
macro empty-object is expanded during compilation, producing a
single "constant" (nil) that is reused and altered each time
initialize is called.
One way to avoid pathological cases like this is to think of
empty-object as a funny kind of constant, not as a memory
allocation construct. You wouldn't use setcar on a constant such
as '(nil), so naturally you won't use it on (empty-object)
either.
This chapter describes how to declare user options for customization, and also customization groups for classifying them. We use the term customization item to include both kinds of customization definitions--as well as face definitions (see section Defining Faces).
All kinds of customization declarations (for variables and groups, and for faces) accept keyword arguments for specifying various information. This section describes some keywords that apply to all kinds.
All of these keywords, except :tag, can be used more than once
in a given item. Each use of the keyword has an independent effect.
The keyword :tag is an exception because any given item can only
display one name.
:tag name
:group group
:group in a defgroup, it makes the new group a subgroup of
group.
If you use this keyword more than once, you can put a single item into
more than one group. Displaying any of those groups will show this
item. Be careful not to overdo this!
:link link-data
(custom-manual info-node)
"(emacs)Top". The link appears as
`[manual]' in the customization buffer.
(info-link info-node)
custom-manual except that the link appears
in the customization buffer with the Info node name.
(url-link url)
:tag name after the first element of the link-data;
for example, (info-link :tag "foo" "(emacs)Top") makes a link to
the Emacs manual which appears in the buffer as `foo'.
An item can have more than one external link; however, most items have
none at all.
:load file
load-library, and only if the file is
not already loaded.
:require feature
require.
The most common reason to use :require is when a variable enables
a feature such as a minor mode, and just setting the variable won't have
any effect unless the code which implements the mode is loaded.
Each Emacs Lisp package should have one main customization group which contains all the options, faces and other groups in the package. If the package has a small number of options and faces, use just one group and put everything in it. When there are more than twelve or so options and faces, then you should structure them into subgroups, and put the subgroups under the package's main customization group. It is OK to put some of the options and faces in the package's main group alongside the subgroups.
The package's main or only group should be a member of one or more of
the standard customization groups. (To display the full list of them,
use M-x customize.) Choose one or more of them (but not too
many), and add your group to each of them using the :group
keyword.
The way to declare new customization groups is with defgroup.
The argument members is a list specifying an initial set of
customization items to be members of the group. However, most often
members is nil, and you specify the group's members by
using the :group keyword when defining those members.
If you want to specify group members through members, each element
should have the form (name widget). Here name
is a symbol, and widget is a widget type for editing that symbol.
Useful widgets are custom-variable for a variable,
custom-face for a face, and custom-group for a group.
In addition to the common keywords (see section Common Keywords for All Kinds of Items), you can
use this keyword in defgroup:
:prefix prefix
The prefix-discarding feature is currently turned off, which means
that :prefix currently has no effect. We did this because we
found that discarding the specified prefixes often led to confusing
names for options. This happened because the people who wrote the
defgroup definitions for various groups added :prefix
keywords whenever they make logical sense--that is, whenever the
variables in the library have a common prefix.
In order to obtain good results with :prefix, it would be
necessary to check the specific effects of discarding a particular
prefix, given the specific items in a group and their names and
documentation. If the resulting text is not clear, then :prefix
should not be used in that case.
It should be possible to recheck all the customization groups, delete
the :prefix specifications which give unclear results, and then
turn this feature back on, if someone would like to do the work.
Use defcustom to declare user-editable variables.
If option is void, defcustom initializes it to
default. default should be an expression to compute the
value; be careful in writing it, because it can be evaluated on more
than one occasion.
defcustom accepts the following additional keywords:
:type type
:options list
hook. In that
case, the elements of list should be functions that are useful as
elements of the hook value. The user is not restricted to using only
these functions, but they are offered as convenient alternatives.
:version version
(defcustom foo-max 34 "*Maximum number of foo's allowed." :type 'integer :group 'foo :version "20.3")
:set setfunction
set-default.
:get getfunction
default-value.
:initialize function
defcustom is evaluated. It should take two arguments, the
symbol and value. Here are some predefined functions meant for use in
this way:
custom-initialize-set
:set function to initialize the variable, but
do not reinitialize it if it is already non-void. This is the default
:initialize function.
custom-initialize-default
custom-initialize-set, but use the function
set-default to set the variable, instead of the variable's
:set function. This is the usual choice for a variable whose
:set function enables or disables a minor mode; with this choice,
defining the variable will not call the minor mode function, but
customizing the variable will do so.
custom-initialize-reset
:set function to initialize the variable. If the
variable is already non-void, reset it by calling the :set
function using the current value (returned by the :get method).
custom-initialize-changed
:set function to initialize the variable, if it is
already set or has been customized; otherwise, just use
set-default.
The :require option is useful for an option that turns on the
operation of a certain feature. Assuming that the package is coded to
check the value of the option, you still need to arrange for the package
to be loaded. You can do that with :require. See section Common Keywords for All Kinds of Items. Here is an example, from the library `paren.el':
(defcustom show-paren-mode nil
"Toggle Show Paren mode@enddots{}"
:set (lambda (symbol value)
(show-paren-mode (or value 0)))
:initialize 'custom-initialize-default
:type 'boolean
:group 'paren-showing
:require 'paren)
Internally, defcustom uses the symbol property
standard-value to record the expression for the default value,
and saved-value to record the value saved by the user with the
customization buffer. The saved-value property is actually a
list whose car is an expression which evaluates to the value.
When you define a user option with defcustom, you must specify
its customization type. That is a Lisp object which describes (1)
which values are legitimate and (2) how to display the value in the
customization buffer for editing.
You specify the customization type in defcustom with the
:type keyword. The argument of :type is evaluated; since
types that vary at run time are rarely useful, normally you use a quoted
constant. For example:
(defcustom diff-command "diff" "*The command to use to run diff." :type '(string) :group 'diff)
In general, a customization type is a list whose first element is a symbol, one of the customization type names defined in the following sections. After this symbol come a number of arguments, depending on the symbol. Between the type symbol and its arguments, you can optionally write keyword-value pairs (see section Type Keywords).
Some of the type symbols do not use any arguments; those are called
simple types. For a simple type, if you do not use any
keyword-value pairs, you can omit the parentheses around the type
symbol. For example just string as a customization type is
equivalent to (string).
This section describes all the simple customization types.
sexp
sexp as a fall-back for any option, if you don't want to
take the time to work out a more specific type to use.
integer
number
string
regexp
string except that the string must be a valid regular
expression.
character
file
(file :must-match t)
directory
hook
:options keyword in a hook variable's
defcustom to specify a list of functions recommended for use in
the hook; see section Defining Customization Variables.
symbol
function
variable
face
boolean
nil or t. Note that by
using choice and const together (see the next section),
you can specify that the value must be nil or t, but also
specify the text to describe each value in a way that fits the specific
meaning of the alternative.
When none of the simple types is appropriate, you can use composite types, which build new types from other types. Here are several ways of doing that:
(restricted-sexp :match-alternatives criteria)
nil or non-nil according to
the argument. Using a predicate in the list says that objects for which
the predicate returns non-nil are acceptable.
'object. This sort of element
in the list says that object itself is an acceptable value.
(restricted-sexp :match-alternatives
(integerp 't 'nil))
allows integers, t and nil as legitimate values.
The customization buffer shows all legitimate values using their read
syntax, and the user edits them textually.
(cons car-type cdr-type)
(cons string
symbol) is a customization type which matches values such as
("foo" . foo).
In the customization buffer, the CAR and the CDR are
displayed and edited separately, each according to the type
that you specify for it.
(list element-types...)
(list integer string function) describes a list of
three elements; the first element must be an integer, the second a
string, and the third a function.
In the customization buffer, each element is displayed and edited
separately, according to the type specified for it.
(vector element-types...)
list except that the value must be a vector instead of a
list. The elements work the same as in list.
(choice alternative-types...)
(choice integer string) allows either an
integer or a string.
In the customization buffer, the user selects one of the alternatives
using a menu, and can then edit the value in the usual way for that
alternative.
Normally the strings in this menu are determined automatically from the
choices; however, you can specify different strings for the menu by
including the :tag keyword in the alternatives. For example, if
an integer stands for a number of spaces, while a string is text to use
verbatim, you might write the customization type this way,
(choice (integer :tag "Number of spaces")
(string :tag "Literal text"))
so that the menu offers `Number of spaces' and `Literal Text'.
In any alternative for which nil is not a valid value, other than
a const, you should specify a valid default for that alternative
using the :value keyword. See section Type Keywords.
(const value)
const is inside of choice. For example,
(choice integer (const nil)) allows either an integer or
nil.
:tag is often used with const, inside of choice.
For example,
(choice (const :tag "Yes" t)
(const :tag "No" nil)
(const :tag "Ask" foo))
describes a variable for which t means yes, nil means no,
and foo means "ask."
(other value)
other is as the last element of choice.
For example,
(choice (const :tag "Yes" t)
(const :tag "No" nil)
(other :tag "Ask" foo))
describes a variable for which t means yes, nil means no,
and anything else means "ask." If the user chooses `Ask' from
the menu of alternatives, that specifies the value foo; but any
other value (not t, nil or foo) displays as
`Ask', just like foo.
(function-item function)
const, but used for values which are functions. This
displays the documentation string as well as the function name.
The documentation string is either the one you specify with
:doc, or function's own documentation string.
(variable-item variable)
const, but used for values which are variable names. This
displays the documentation string as well as the variable name. The
documentation string is either the one you specify with :doc, or
variable's own documentation string.
(set elements...)
(repeat element-type)
The :inline feature lets you splice a variable number of
elements into the middle of a list or vector. You use it in a
set, choice or repeat type which appears among the
element-types of a list or vector.
Normally, each of the element-types in a list or vector
describes one and only one element of the list or vector. Thus, if an
element-type is a repeat, that specifies a list of unspecified
length which appears as one element.
But when the element-type uses :inline, the value it matches is
merged directly into the containing sequence. For example, if it
matches a list with three elements, those become three elements of the
overall sequence. This is analogous to using `,@' in the backquote
construct.
For example, to specify a list whose first element must be t
and whose remaining arguments should be zero or more of foo and
bar, use this customization type:
(list (const t) (set :inline t foo bar))
This matches values such as (t), (t foo), (t bar)
and (t foo bar).
When the element-type is a choice, you use :inline not
in the choice itself, but in (some of) the alternatives of the
choice. For example, to match a list which must start with a
file name, followed either by the symbol t or two strings, use
this customization type:
(list file
(choice (const t)
(list :inline t string string)))
If the user chooses the first alternative in the choice, then the
overall list has two elements and the second element is t. If
the user chooses the second alternative, then the overall list has three
elements and the second and third must be strings.
You can specify keyword-argument pairs in a customization type after the type name symbol. Here are the keywords you can use, and their meanings:
:value default
choice; it specifies the default value to use, at first, if and
when the user selects this alternative with the menu in the
customization buffer.
Of course, if the actual value of the option fits this alternative, it
will appear showing the actual value, not default.
If nil is not a valid value for the alternative, then it is
essential to specify a valid default with :value.
:format format-string
:action
attribute specifies what the button will do if the user invokes it;
its value is a function which takes two arguments--the widget which
the button appears in, and the event.
There is no way to specify two different buttons with different
actions.
:sample-face.
:tag
keyword.
:action action
:button-face face
:button-prefix prefix
:button-suffix suffix
nil
:tag tag
:doc doc
:format, and use `%d' or `%h'
in that value.
The usual reason to specify a documentation string for a type is to
provide more information about the meanings of alternatives inside a
:choice type or the parts of some other composite type.
:help-echo motion-doc
widget-forward or
widget-backward, it will display the string motion-doc
in the echo area.
:match function
nil if
the value is acceptable.
Loading a file of Lisp code means bringing its contents into the Lisp environment in the form of Lisp objects. Emacs finds and opens the file, reads the text, evaluates each form, and then closes the file.
The load functions evaluate all the expressions in a file just
as the eval-current-buffer function evaluates all the
expressions in a buffer. The difference is that the load functions
read and evaluate the text in the file as found on disk, not the text
in an Emacs buffer.
The loaded file must contain Lisp expressions, either as source code or as byte-compiled code. Each form in the file is called a top-level form. There is no special format for the forms in a loadable file; any form in a file may equally well be typed directly into a buffer and evaluated there. (Indeed, most code is tested this way.) Most often, the forms are function definitions and variable definitions.
A file containing Lisp code is often called a library. Thus, the "Rmail library" is a file containing code for Rmail mode. Similarly, a "Lisp library directory" is a directory of files containing Lisp code.
Emacs Lisp has several interfaces for loading. For example,
autoload creates a placeholder object for a function defined in a
file; trying to call the autoloading function loads the file to get the
function's real definition (see section Autoload). require loads a
file if it isn't already loaded (see section Features). Ultimately,
all these facilities call the load function to do the work.
To find the file, load first looks for a file named
`filename.elc', that is, for a file whose name is
filename with `.elc' appended. If such a file exists, it is
loaded. If there is no file by that name, then load looks for a
file named `filename.el'. If that file exists, it is loaded.
Finally, if neither of those names is found, load looks for a
file named filename with nothing appended, and loads it if it
exists. (The load function is not clever about looking at
filename. In the perverse case of a file named `foo.el.el',
evaluation of (load "foo.el") will indeed find it.)
If the optional argument nosuffix is non-nil, then the
suffixes `.elc' and `.el' are not tried. In this case, you
must specify the precise file name you want. By specifying the precise
file name and using t for nosuffix, you can prevent
perverse file names such as `foo.el.el' from being tried.
If the optional argument must-suffix is non-nil, then
load insists that the file name used must end in either
`.el' or `.elc', unless it contains an explicit directory
name. If filename does not contain an explicit directory name,
and does not end in a suffix, then load insists on adding one.
If filename is a relative file name, such as `foo' or
`baz/foo.bar', load searches for the file using the variable
load-path. It appends filename to each of the directories
listed in load-path, and loads the first file it finds whose name
matches. The current default directory is tried only if it is specified
in load-path, where nil stands for the default directory.
load tries all three possible suffixes in the first directory in
load-path, then all three suffixes in the second directory, and
so on. See section Library Search.
If you get a warning that `foo.elc' is older than `foo.el', it means you should consider recompiling `foo.el'. See section Byte Compilation.
When loading a source file (not compiled), load performs
character set translation just as Emacs would do when visiting the file.
See section Coding Systems.
Messages like `Loading foo...' and `Loading foo...done' appear
in the echo area during loading unless nomessage is
non-nil.
Any unhandled errors while loading a file terminate loading. If the
load was done for the sake of autoload, any function definitions
made during the loading are undone.
If load can't find the file to load, then normally it signals the
error file-error (with `Cannot open load file
filename'). But if missing-ok is non-nil, then
load just returns nil.
You can use the variable load-read-function to specify a function
for load to use instead of read for reading expressions.
See below.
load returns t if the file loads successfully.
load-path is not used, and suffixes are not appended. Use this
command if you wish to specify precisely the file name to load.
load, except in how it reads its argument interactively.
nil if Emacs is in the process of loading a
file, and it is nil otherwise.
load and eval-region to use instead of read.
The function should accept one argument, just as read does.
Normally, the variable's value is nil, which means those
functions should use read.
Note: Instead of using this variable, it is cleaner to use
another, newer feature: to pass the function as the read-function
argument to eval-region. See section Eval.
For information about how load is used in building Emacs, see
section Building Emacs.
When Emacs loads a Lisp library, it searches for the library
in a list of directories specified by the variable load-path.
load. Each element is a string (which must be
a directory name) or nil (which stands for the current working
directory).
The value of load-path is initialized from the environment
variable EMACSLOADPATH, if that exists; otherwise its default
value is specified in `emacs/src/paths.h' when Emacs is built.
Then the list is expanded by adding subdirectories of the directories
in the list.
The syntax of EMACSLOADPATH is the same as used for PATH;
`:' (or `;', according to the operating system) separates
directory names, and `.' is used for the current default directory.
Here is an example of how to set your EMACSLOADPATH variable from
a csh `.login' file:
setenv EMACSLOADPATH .:/user/bil/emacs:/usr/local/share/emacs/20.3/lisp
Here is how to set it using sh:
export EMACSLOADPATH EMACSLOADPATH=.:/user/bil/emacs:/usr/local/share/emacs/20.3/lisp
Here is an example of code you can place in a `.emacs' file to add
several directories to the front of your default load-path:
(setq load-path
(append (list nil "/user/bil/emacs"
"/usr/local/lisplib"
"~/emacs")
load-path))
In this example, the path searches the current working directory first, followed then by the `/user/bil/emacs' directory, the `/usr/local/lisplib' directory, and the `~/emacs' directory, which are then followed by the standard directories for Lisp code.
Dumping Emacs uses a special value of load-path. If the value of
load-path at the end of dumping is unchanged (that is, still the
same special value), the dumped Emacs switches to the ordinary
load-path value when it starts up, as described above. But if
load-path has any other value at the end of dumping, that value
is used for execution of the dumped Emacs also.
Therefore, if you want to change load-path temporarily for
loading a few libraries in `site-init.el' or `site-load.el',
you should bind load-path locally with let around the
calls to load.
The default value of load-path, when running an Emacs which has
been installed on the system, includes two special directories (and
their subdirectories as well):
"/usr/local/share/emacs/version/site-lisp"
and
"/usr/local/share/emacs/site-lisp"
The first one is for locally installed packages for a particular Emacs version; the second is for locally installed packages meant for use with all installed Emacs versions.
There are several reasons why a Lisp package that works well in one Emacs version can cause trouble in another. Sometimes packages need updating for incompatible changes in Emacs; sometimes they depend on undocumented internal Emacs data that can change without notice; sometimes a newer Emacs version incorporates a version of the package, and should be used only with that version.
Emacs finds these directories' subdirectories and adds them to
load-path when it starts up. Both immediate subdirectories and
subdirectories multiple levels down are added to load-path.
Not all subdirectories are included, though. Subdirectories whose names do not start with a letter or digit are excluded. Subdirectories named `RCS' are excluded. Also, a subdirectory which contains a file named `.nosearch' is excluded. You can use these methods to prevent certain subdirectories of the `site-lisp' directories from being searched.
If you run Emacs from the directory where it was built--that is, an
executable that has not been formally installed--then load-path
normally contains two additional directories. These are the lisp
and site-lisp subdirectories of the main build directory. (Both
are represented as absolute file names.)
load does, and the
argument nosuffix has the same meaning as in load: don't
add suffixes `.elc' or `.el' to the specified name
library.
If the path is non-nil, that list of directories is used
instead of load-path.
When locate-library is called from a program, it returns the file
name as a string. When the user runs locate-library
interactively, the argument interactive-call is t, and this
tells locate-library to display the file name in the echo area.
When Emacs Lisp programs contain string constants with non-ASCII characters, these can be represented within Emacs either as unibyte strings or as multibyte strings (see section Text Representations). Which representation is used depends on how the file is read into Emacs. If it is read with decoding into multibyte representation, the text of the Lisp program will be multibyte text, and its string constants will be multibyte strings. If a file containing Latin-1 characters (for example) is read without decoding, the text of the program will be unibyte text, and its string constants will be unibyte strings. See section Coding Systems.
To make the results more predictable, Emacs always performs decoding into the multibyte representation when loading Lisp files, even if it was started with the `--unibyte' option. This means that string constants with non-ASCII characters translate into multibyte strings. The only exception is when a particular file specifies no decoding.
The reason Emacs is designed this way is so that Lisp programs give
predictable results, regardless of how Emacs was started. In addition,
this enables programs that depend on using multibyte text to work even
in a unibyte Emacs. Of course, such programs should be designed to
notice whether the user prefers unibyte or multibyte text, by checking
default-enable-multibyte-characters, and convert representations
appropriately.
In most Emacs Lisp programs, the fact that non-ASCII strings are multibyte strings should not be noticeable, since inserting them in unibyte buffers converts them to unibyte automatically. However, if this does make a difference, you can force a particular Lisp file to be interpreted as unibyte by writing `-*-unibyte: t;-*-' in a comment on the file's first line. With that designator, the file will be unconditionally be interpreted as unibyte, even in an ordinary multibyte Emacs session.
The autoload facility allows you to make a function or macro known in Lisp, but put off loading the file that defines it. The first call to the function automatically reads the proper file to install the real definition and other associated code, then runs the real definition as if it had been loaded all along.
There are two ways to set up an autoloaded function: by calling
autoload, and by writing a special "magic" comment in the
source before the real definition. autoload is the low-level
primitive for autoloading; any Lisp program can call autoload at
any time. Magic comments are the most convenient way to make a function
autoload, for packages installed along with Emacs. These comments do
nothing on their own, but they serve as a guide for the command
update-file-autoloads, which constructs calls to autoload
and arranges to execute them when Emacs is built.
If filename does not contain either a directory name, or the
suffix .el or .elc, then autoload insists on adding
one of these suffixes, and it will not load from a file whose name is
just filename with no added suffix.
The argument docstring is the documentation string for the
function. Normally, this should be identical to the documentation string
in the function definition itself. Specifying the documentation string
in the call to autoload makes it possible to look at the
documentation without loading the function's real definition.
If interactive is non-nil, that says function can be
called interactively. This lets completion in M-x work without
loading function's real definition. The complete interactive
specification is not given here; it's not needed unless the user
actually calls function, and when that happens, it's time to load
the real definition.
You can autoload macros and keymaps as well as ordinary functions.
Specify type as macro if function is really a macro.
Specify type as keymap if function is really a
keymap. Various parts of Emacs need to know this information without
loading the real definition.
An autoloaded keymap loads automatically during key lookup when a prefix
key's binding is the symbol function. Autoloading does not occur
for other kinds of access to the keymap. In particular, it does not
happen when a Lisp program gets the keymap from the value of a variable
and calls define-key; not even if the variable name is the same
symbol function.
If function already has a non-void function definition that is not
an autoload object, autoload does nothing and returns nil.
If the function cell of function is void, or is already an autoload
object, then it is defined as an autoload object like this:
(autoload filename docstring interactive type)
For example,
(symbol-function 'run-prolog)
=> (autoload "prolog" 169681 t nil)
In this case, "prolog" is the name of the file to load, 169681
refers to the documentation string in the
`emacs/etc/DOC-version' file (see section Documentation Basics),
t means the function is interactive, and nil that it is
not a macro or a keymap.
The autoloaded file usually contains other definitions and may require
or provide one or more features. If the file is not completely loaded
(due to an error in the evaluation of its contents), any function
definitions or provide calls that occurred during the load are
undone. This is to ensure that the next attempt to call any function
autoloading from this file will try again to load the file. If not for
this, then some of the functions in the file might be defined by the
aborted load, but fail to work properly for the lack of certain
subroutines not loaded successfully because they come later in the file.
If the autoloaded file fails to define the desired Lisp function or
macro, then an error is signaled with data "Autoloading failed to
define function function-name".
A magic autoload comment consists of `;;;###autoload', on a line
by itself, just before the real definition of the function in its
autoloadable source file. The command M-x update-file-autoloads
writes a corresponding autoload call into `loaddefs.el'.
Building Emacs loads `loaddefs.el' and thus calls autoload.
M-x update-directory-autoloads is even more powerful; it updates
autoloads for all files in the current directory.
The same magic comment can copy any kind of form into `loaddefs.el'. If the form following the magic comment is not a function definition, it is copied verbatim. You can also use a magic comment to execute a form at build time without executing it when the file itself is loaded. To do this, write the form on the same line as the magic comment. Since it is in a comment, it does nothing when you load the source file; but M-x update-file-autoloads copies it to `loaddefs.el', where it is executed while building Emacs.
The following example shows how doctor is prepared for
autoloading with a magic comment:
;;;###autoload (defun doctor () "Switch to *doctor* buffer and start giving psychotherapy." (interactive) (switch-to-buffer "*doctor*") (doctor-mode))
Here's what that produces in `loaddefs.el':
(autoload 'doctor "doctor" "\ Switch to *doctor* buffer and start giving psychotherapy." t)
The backslash and newline immediately following the double-quote are a
convention used only in the preloaded Lisp files such as
`loaddefs.el'; they tell make-docfile to put the
documentation string in the `etc/DOC' file. See section Building Emacs.
You can load a given file more than once in an Emacs session. For example, after you have rewritten and reinstalled a function definition by editing it in a buffer, you may wish to return to the original version; you can do this by reloading the file it came from.
When you load or reload files, bear in mind that the load and
load-library functions automatically load a byte-compiled file
rather than a non-compiled file of similar name. If you rewrite a file
that you intend to save and reinstall, you need to byte-compile the new
version; otherwise Emacs will load the older, byte-compiled file instead
of your newer, non-compiled file! If that happens, the message
displayed when loading the file includes, `(compiled; note, source is
newer)', to remind you to recompile it.
When writing the forms in a Lisp library file, keep in mind that the
file might be loaded more than once. For example, think about whether
each variable should be reinitialized when you reload the library;
defvar does not change the value if the variable is already
initialized. (See section Defining Global Variables.)
The simplest way to add an element to an alist is like this:
(setq minor-mode-alist
(cons '(leif-mode " Leif") minor-mode-alist))
But this would add multiple elements if the library is reloaded. To avoid the problem, write this:
(or (assq 'leif-mode minor-mode-alist)
(setq minor-mode-alist
(cons '(leif-mode " Leif") minor-mode-alist)))
To add an element to a list just once, you can also use add-to-list
(see section How to Alter a Variable Value).
Occasionally you will want to test explicitly whether a library has already been loaded. Here's one way to test, in a library, whether it has been loaded before:
(defvar foo-was-loaded nil) (unless foo-was-loaded execute-first-time-only (setq foo-was-loaded t))
If the library uses provide to provide a named feature, you can
use featurep earlier in the file to test whether the
provide call has been executed before.
provide and require are an alternative to
autoload for loading files automatically. They work in terms of
named features. Autoloading is triggered by calling a specific
function, but a feature is loaded the first time another program asks
for it by name.
A feature name is a symbol that stands for a collection of functions, variables, etc. The file that defines them should provide the feature. Another program that uses them may ensure they are defined by requiring the feature. This loads the file of definitions if it hasn't been loaded already.
To require the presence of a feature, call require with the
feature name as argument. require looks in the global variable
features to see whether the desired feature has been provided
already. If not, it loads the feature from the appropriate file. This
file should call provide at the top level to add the feature to
features; if it fails to do so, require signals an error.
For example, in `emacs/lisp/prolog.el',
the definition for run-prolog includes the following code:
(defun run-prolog () "Run an inferior Prolog process, with I/O via buffer *prolog*." (interactive) (require 'comint) (switch-to-buffer (make-comint "prolog" prolog-program-name)) (inferior-prolog-mode))
The expression (require 'comint) loads the file `comint.el'
if it has not yet been loaded. This ensures that make-comint is
defined. Features are normally named after the files that provide them,
so that require need not be given the file name.
The `comint.el' file contains the following top-level expression:
(provide 'comint)
This adds comint to the global features list, so that
(require 'comint) will henceforth know that nothing needs to be
done.
When require is used at top level in a file, it takes effect
when you byte-compile that file (see section Byte Compilation) as well as
when you load it. This is in case the required package contains macros
that the byte compiler must know about.
Although top-level calls to require are evaluated during
byte compilation, provide calls are not. Therefore, you can
ensure that a file of definitions is loaded before it is byte-compiled
by including a provide followed by a require for the same
feature, as in the following example.
(provide 'my-feature) ; Ignored by byte compiler,
; evaluated by load.
(require 'my-feature) ; Evaluated by byte compiler.
The compiler ignores the provide, then processes the
require by loading the file in question. Loading the file does
execute the provide call, so the subsequent require call
does nothing when the file is loaded.
The direct effect of calling provide is to add feature to
the front of the list features if it is not already in the list.
The argument feature must be a symbol. provide returns
feature.
features
=> (bar bish)
(provide 'foo)
=> foo
features
=> (foo bar bish)
When a file is loaded to satisfy an autoload, and it stops due to an
error in the evaluating its contents, any function definitions or
provide calls that occurred during the load are undone.
See section Autoload.
(featurep feature); see below). The
argument feature must be a symbol.
If the feature is not present, then require loads filename
with load. If filename is not supplied, then the name of
the symbol feature is used as the base file name to load.
However, in this case, require insists on finding feature
with an added suffix; a file whose name is just feature won't be
used.
If loading the file fails to provide feature, require
signals an error, `Required feature feature was not
provided'.
t if feature has been provided in the
current Emacs session (i.e., if feature is a member of
features.)
provide. The order of the elements in the
features list is not significant.
You can discard the functions and variables loaded by a library to
reclaim memory for other Lisp objects. To do this, use the function
unload-feature:
defun, defalias, defsubst,
defmacro, defconst, defvar, and defcustom.
It then restores any autoloads formerly associated with those symbols.
(Loading saves these in the autoload property of the symbol.)
Before restoring the previous definitions, unload-feature runs
remove-hook to remove functions in the library from certain
hooks. These hooks include variables whose names end in `hook' or
`-hooks', plus those listed in loadhist-special-hooks. This
is to prevent Emacs from ceasing to function because important hooks
refer to functions that are no longer defined.
If these measures are not sufficient to prevent malfunction, a library
can define an explicit unload hook. If feature-unload-hook
is defined, it is run as a normal hook before restoring the previous
definitions, instead of the usual hook-removing actions. The
unload hook ought to undo all the global state changes made by the
library that might cease to work once the library is unloaded.
Ordinarily, unload-feature refuses to unload a library on which
other loaded libraries depend. (A library a depends on library
b if a contains a require for b.) If the
optional argument force is non-nil, dependencies are
ignored and you can unload any library.
The unload-feature function is written in Lisp; its actions are
based on the variable load-history.
Each element is a list and describes one library. The CAR of the list is the name of the library, as a string. The rest of the list is composed of these kinds of objects:
(require . feature) indicating
features that were required.
(provide . feature) indicating
features that were provided.
The value of load-history may have one element whose CAR is
nil. This element describes definitions made with
eval-buffer on a buffer that is not visiting a file.
The command eval-region updates load-history, but does so
by adding the symbols defined to the element for the file being visited,
rather than replacing that element. See section Eval.
Preloaded libraries don't contribute to load-history.
You can ask for code to be executed if and when a particular library is
loaded, by calling eval-after-load.
The library name library must exactly match the argument of
load. To get the proper results when an installed library is
found by searching load-path, you should not include any
directory names in library.
An error in form does not undo the load, but does prevent execution of the rest of form.
In general, well-designed Lisp programs should not use this feature.
The clean and modular ways to interact with a Lisp library are (1)
examine and set the library's variables (those which are meant for
outside use), and (2) call the library's functions. If you wish to
do (1), you can do it immediately--there is no need to wait for when
the library is loaded. To do (2), you must load the library (preferably
with require).
But it is OK to use eval-after-load in your personal
customizations if you don't feel they must meet the design standards for
programs meant for wider use.
(filename forms...)
The function load checks after-load-alist in order to
implement eval-after-load.
Emacs Lisp has a compiler that translates functions written in Lisp into a special representation called byte-code that can be executed more efficiently. The compiler replaces Lisp function definitions with byte-code. When a byte-code function is called, its definition is evaluated by the byte-code interpreter.
Because the byte-compiled code is evaluated by the byte-code interpreter, instead of being executed directly by the machine's hardware (as true compiled code is), byte-code is completely transportable from machine to machine without recompilation. It is not, however, as fast as true compiled code.
Compiling a Lisp file with the Emacs byte compiler always reads the file as multibyte text, even if Emacs was started with `--unibyte', unless the file specifies otherwise. This is so that compilation gives results compatible with running the same file without compilation. See section Loading Non-ASCII Characters.
In general, any version of Emacs can run byte-compiled code produced by recent earlier versions of Emacs, but the reverse is not true. A major incompatible change was introduced in Emacs version 19.29, and files compiled with versions since that one will definitely not run in earlier versions unless you specify a special option. See section Documentation Strings and Compilation. In addition, the modifier bits in keyboard characters were renumbered in Emacs 19.29; as a result, files compiled in versions before 19.29 will not work in subsequent versions if they contain character constants with modifier bits.
See section Debugging Problems in Compilation, for how to investigate errors occurring in byte compilation.
A byte-compiled function is not as efficient as a primitive function written in C, but runs much faster than the version written in Lisp. Here is an example:
(defun silly-loop (n)
"Return time before and after N iterations of a loop."
(let ((t1 (current-time-string)))
(while (> (setq n (1- n))
0))
(list t1 (current-time-string))))
=> silly-loop
(silly-loop 100000)
=> ("Fri Mar 18 17:25:57 1994"
"Fri Mar 18 17:26:28 1994") ; 31 seconds
(byte-compile 'silly-loop)
=> [Compiled code not shown]
(silly-loop 100000)
=> ("Fri Mar 18 17:26:52 1994"
"Fri Mar 18 17:26:58 1994") ; 6 seconds
In this example, the interpreted code required 31 seconds to run, whereas the byte-compiled code required 6 seconds. These results are representative, but actual results will vary greatly.
You can byte-compile an individual function or macro definition with
the byte-compile function. You can compile a whole file with
byte-compile-file, or several files with
byte-recompile-directory or batch-byte-compile.
The byte compiler produces error messages and warnings about each file in a buffer called `*Compile-Log*'. These report things in your program that suggest a problem but are not necessarily erroneous.
Be careful when writing macro calls in files that you may someday byte-compile. Macro calls are expanded when they are compiled, so the macros must already be defined for proper compilation. For more details, see section Macros and Byte Compilation.
Normally, compiling a file does not evaluate the file's contents or
load the file. But it does execute any require calls at top
level in the file. One way to ensure that necessary macro definitions
are available during compilation is to require the file that defines
them (see section Features). To avoid loading the macro definition files
when someone runs the compiled program, write
eval-when-compile around the require calls (see section Evaluation During Compilation).
byte-compile returns the new, compiled definition of
symbol.
If symbol's definition is a byte-code function object,
byte-compile does nothing and returns nil. Lisp records
only one function definition for any symbol, and if that is already
compiled, non-compiled code is not available anywhere. So there is no
way to "compile the same definition again."
(defun factorial (integer)
"Compute factorial of INTEGER."
(if (= 1 integer) 1
(* integer (factorial (1- integer)))))
=> factorial
(byte-compile 'factorial)
=>
#[(integer)
"^H\301U\203^H^@\301\207\302^H\303^HS!\"\207"
[integer 1 * factorial]
4 "Compute factorial of INTEGER."]
The result is a byte-code function object. The string it contains is the actual byte-code; each character in it is an instruction or an operand of an instruction. The vector contains all the constants, variable names and function names used by the function, except for certain primitives that are coded as special instructions.
Compilation works by reading the input file one form at a time. If it is a definition of a function or macro, the compiled function or macro definition is written out. Other forms are batched together, then each batch is compiled, and written so that its compiled code will be executed when the file is read. All comments are discarded when the input file is read.
This command returns t. When called interactively, it prompts
for the file name.
% ls -l push*
-rw-r--r-- 1 lewis 791 Oct 5 20:31 push.el
(byte-compile-file "~/emacs/push.el")
=> t
% ls -l push*
-rw-r--r-- 1 lewis 791 Oct 5 20:31 push.el
-rw-rw-rw- 1 lewis 638 Oct 8 20:25 push.elc
When a `.el' file has no corresponding `.elc' file, flag
says what to do. If it is nil, these files are ignored. If it
is non-nil, the user is asked whether to compile each such file.
The returned value of this command is unpredictable.
byte-compile-file on files specified on the
command line. This function must be used only in a batch execution of
Emacs, as it kills Emacs on completion. An error in one file does not
prevent processing of subsequent files, but no output file will be
generated for it, and the Emacs process will terminate with a nonzero
status code.
% emacs -batch -f batch-byte-compile *.el
byte-code. Don't call
this function yourself--only the byte compiler knows how to generate
valid calls to this function.
In Emacs version 18, byte-code was always executed by way of a call to
the function byte-code. Nowadays, byte-code is usually executed
as part of a byte-code function object, and only rarely through an
explicit call to byte-code.
Functions and variables loaded from a byte-compiled file access their documentation strings dynamically from the file whenever needed. This saves space within Emacs, and makes loading faster because the documentation strings themselves need not be processed while loading the file. Actual access to the documentation strings becomes slower as a result, but this normally is not enough to bother users.
Dynamic access to documentation strings does have drawbacks:
If your site installs Emacs following the usual procedures, these problems will never normally occur. Installing a new version uses a new directory with a different name; as long as the old version remains installed, its files will remain unmodified in the places where they are expected to be.
However, if you have built Emacs yourself and use it from the directory where you built it, you will experience this problem occasionally if you edit and recompile Lisp files. When it happens, you can cure the problem by reloading the file after recompiling it.
Byte-compiled files made with recent versions of Emacs (since 19.29)
will not load into older versions because the older versions don't
support this feature. You can turn off this feature at compile time by
setting byte-compile-dynamic-docstrings to nil; then you
can compile files that will load into older Emacs versions. You can do
this globally, or for one source file by specifying a file-local binding
for the variable. One way to do that is by adding this string to the
file's first line:
-*-byte-compile-dynamic-docstrings: nil;-*-
nil, the byte compiler generates compiled files
that are set up for dynamic loading of documentation strings.
The dynamic documentation string feature writes compiled files that use a special Lisp reader construct, `#@count'. This construct skips the next count characters. It also uses the `#$' construct, which stands for "the name of this file, as a string." It is usually best not to use these constructs in Lisp source files, since they are not designed to be clear to humans reading the file.
When you compile a file, you can optionally enable the dynamic function loading feature (also known as lazy loading). With dynamic function loading, loading the file doesn't fully read the function definitions in the file. Instead, each function definition contains a place-holder which refers to the file. The first time each function is called, it reads the full definition from the file, to replace the place-holder.
The advantage of dynamic function loading is that loading the file becomes much faster. This is a good thing for a file which contains many separate user-callable functions, if using one of them does not imply you will probably also use the rest. A specialized mode which provides many keyboard commands often has that usage pattern: a user may invoke the mode, but use only a few of the commands it provides.
The dynamic loading feature has certain disadvantages:
These problems will never happen in normal circumstances with installed Emacs files. But they are quite likely to happen with Lisp files that you are changing. The easiest way to prevent these problems is to reload the new compiled file immediately after each recompilation.
The byte compiler uses the dynamic function loading feature if the
variable byte-compile-dynamic is non-nil at compilation
time. Do not set this variable globally, since dynamic loading is
desirable only for certain files. Instead, enable the feature for
specific source files with file-local variable bindings. For example,
you could do it by writing this text in the source file's first line:
-*-byte-compile-dynamic: t;-*-
nil, the byte compiler generates compiled files
that are set up for dynamic function loading.
These features permit you to write code to be evaluated during compilation of a program.
You can get a similar result by putting body in a separate file
and referring to that file with require. That method is
preferable when body is large.
Common Lisp Note: At top level, this is analogous to the Common
Lisp idiom (eval-when (compile eval) ...). Elsewhere, the
Common Lisp `#.' reader macro (but not when interpreting) is closer
to what eval-when-compile does.
Byte-compiled functions have a special data type: they are byte-code function objects.
Internally, a byte-code function object is much like a vector; however, the evaluator handles this data type specially when it appears as a function to be called. The printed representation for a byte-code function object is like that for a vector, with an additional `#' before the opening `['.
A byte-code function object must have at least four elements; there is no maximum number, but only the first six elements have any normal use. They are:
nil. The value may
be a number or a list, in case the documentation string is stored in a
file. Use the function documentation to get the real
documentation string (see section Access to Documentation Strings).
nil for a function that isn't interactive.
Here's an example of a byte-code function object, in printed
representation. It is the definition of the command
backward-sexp.
#[(&optional arg) "^H\204^F^@\301^P\302^H[!\207" [arg 1 forward-sexp] 2 254435 "p"]
The primitive way to create a byte-code object is with
make-byte-code:
You should not try to come up with the elements for a byte-code function yourself, because if they are inconsistent, Emacs may crash when you call the function. Always leave it to the byte compiler to create these objects; it makes the elements consistent (we hope).
You can access the elements of a byte-code object using aref;
you can also use vconcat to create a vector with the same
elements.
People do not write byte-code; that job is left to the byte compiler. But we provide a disassembler to satisfy a cat-like curiosity. The disassembler converts the byte-compiled code into humanly readable form.
The byte-code interpreter is implemented as a simple stack machine. It pushes values onto a stack of its own, then pops them off to use them in calculations whose results are themselves pushed back on the stack. When a byte-code function returns, it pops a value off the stack and returns it as the value of the function.
In addition to the stack, byte-code functions can use, bind, and set ordinary Lisp variables, by transferring values between variables and the stack.
standard-output. The
argument object can be a function name or a lambda expression.
As a special exception, if this function is used interactively, it outputs to a buffer named `*Disassemble*'.
Here are two examples of using the disassemble function. We
have added explanatory comments to help you relate the byte-code to the
Lisp source; these do not appear in the output of disassemble.
These examples show unoptimized byte-code. Nowadays byte-code is
usually optimized, but we did not want to rewrite these examples, since
they still serve their purpose.
(defun factorial (integer)
"Compute factorial of an integer."
(if (= 1 integer) 1
(* integer (factorial (1- integer)))))
=> factorial
(factorial 4)
=> 24
(disassemble 'factorial)
-| byte-code for factorial:
doc: Compute factorial of an integer.
args: (integer)
0 constant 1 ; Push 1 onto stack.
1 varref integer ; Get value of integer
; from the environment
; and push the value
; onto the stack.
2 eqlsign ; Pop top two values off stack,
; compare them,
; and push result onto stack.
3 goto-if-nil 10 ; Pop and test top of stack;
; if nil, go to 10,
; else continue.
6 constant 1 ; Push 1 onto top of stack.
7 goto 17 ; Go to 17 (in this case, 1 will be
; returned by the function).
10 constant * ; Push symbol * onto stack.
11 varref integer ; Push value of integer onto stack.
12 constant factorial ; Push factorial onto stack.
13 varref integer ; Push value of integer onto stack.
14 sub1 ; Pop integer, decrement value,
; push new value onto stack.
; Stack now contains:
; - decremented value of integer
; - factorial
; - value of integer
; - *
15 call 1 ; Call function factorial using
; the first (i.e., the top) element
; of the stack as the argument;
; push returned value onto stack.
; Stack now contains:
; - result of recursive
; call to factorial
; - value of integer
; - *
16 call 2 ; Using the first two
; (i.e., the top two)
; elements of the stack
; as arguments,
; call the function *,
; pushing the result onto the stack.
17 return ; Return the top element
; of the stack.
=> nil
The silly-loop function is somewhat more complex:
(defun silly-loop (n)
"Return time before and after N iterations of a loop."
(let ((t1 (current-time-string)))
(while (> (setq n (1- n))
0))
(list t1 (current-time-string))))
=> silly-loop
(disassemble 'silly-loop)
-| byte-code for silly-loop:
doc: Return time before and after N iterations of a loop.
args: (n)
0 constant current-time-string ; Push
; current-time-string
; onto top of stack.
1 call 0 ; Call current-time-string
; with no argument,
; pushing result onto stack.
2 varbind t1 ; Pop stack and bind t1
; to popped value.
3 varref n ; Get value of n from
; the environment and push
; the value onto the stack.
4 sub1 ; Subtract 1 from top of stack.
5 dup ; Duplicate the top of the stack;
; i.e., copy the top of
; the stack and push the
; copy onto the stack.
6 varset n ; Pop the top of the stack,
; and bind n to the value.
; In effect, the sequence dup varset
; copies the top of the stack
; into the value of n
; without popping it.
7 constant 0 ; Push 0 onto stack.
8 gtr ; Pop top two values off stack,
; test if n is greater than 0
; and push result onto stack.
9 goto-if-nil-else-pop 17 ; Goto 17 if n <= 0
; (this exits the while loop).
; else pop top of stack
; and continue
12 constant nil ; Push nil onto stack
; (this is the body of the loop).
13 discard ; Discard result of the body
; of the loop (a while loop
; is always evaluated for
; its side effects).
14 goto 3 ; Jump back to beginning
; of while loop.
17 discard ; Discard result of while loop
; by popping top of stack.
; This result is the value nil that
; was not popped by the goto at 9.
18 varref t1 ; Push value of t1 onto stack.
19 constant current-time-string ; Push
; current-time-string
; onto top of stack.
20 call 0 ; Call current-time-string again.
21 list2 ; Pop top two elements off stack,
; create a list of them,
; and push list onto stack.
22 unbind 1 ; Unbind t1 in local environment.
23 return ; Return value of the top of stack.
=> nil
The advice feature lets you add to the existing definition of a function, by advising the function. This is a clean method for a library to customize functions defined by other parts of Emacs--cleaner than redefining the whole function.
Each function can have multiple pieces of advice, separately defined. Each defined piece of advice can be enabled or disabled explicitly. The enabled pieces of advice for any given function actually take effect when you activate advice for that function, or when that function is subsequently defined or redefined.
Usage Note: Advice is useful for altering the behavior of existing calls to an existing function. If you want the new behavior for new calls, or for key bindings, it is cleaner to define a new function (or a new command) which uses the existing function.
The command next-line moves point down vertically one or more
lines; it is the standard binding of C-n. When used on the last
line of the buffer, this command inserts a newline to create a line to
move to (if next-line-add-newlines is non-nil).
Suppose you wanted to add a similar feature to previous-line,
which would insert a new line at the beginning of the buffer for the
command to move to. How could you do this?
You could do it by redefining the whole function, but that is not modular. The advice feature provides a cleaner alternative: you can effectively add your code to the existing function definition, without actually changing or even seeing that definition. Here is how to do this:
(defadvice previous-line (before next-line-at-end (arg))
"Insert an empty line when moving up from the top line."
(if (and next-line-add-newlines (= arg 1)
(save-excursion (beginning-of-line) (bobp)))
(progn
(beginning-of-line)
(newline))))
This expression defines a piece of advice for the function
previous-line. This piece of advice is named
next-line-at-end, and the symbol before says that it is
before-advice which should run before the regular definition of
previous-line. (arg) specifies how the advice code can
refer to the function's arguments.
When this piece of advice runs, it creates an additional line, in the situation where that is appropriate, but does not move point to that line. This is the correct way to write the advice, because the normal definition will run afterward and will move back to the newly inserted line.
Defining the advice doesn't immediately change the function
previous-line. That happens when you activate the advice,
like this:
(ad-activate 'previous-line)
This is what actually begins to use the advice that has been defined so
far for the function previous-line. Henceforth, whenever that
function is run, whether invoked by the user with C-p or
M-x, or called from Lisp, it runs the advice first, and its
regular definition second.
This example illustrates before-advice, which is one class of advice: it runs before the function's base definition. There are two other advice classes: after-advice, which runs after the base definition, and around-advice, which lets you specify an expression to wrap around the invocation of the base definition.
To define a piece of advice, use the macro defadvice. A call
to defadvice has the following syntax, which is based on the
syntax of defun and defmacro, but adds more:
(defadvice function (class name
[position] [arglist]
flags...)
[documentation-string]
[interactive-form]
body-forms...)
Here, function is the name of the function (or macro or special form) to be advised. From now on, we will write just "function" when describing the entity being advised, but this always includes macros and special forms.
class specifies the class of the advice--one of before,
after, or around. Before-advice runs before the function
itself; after-advice runs after the function itself; around-advice is
wrapped around the execution of the function itself. After-advice and
around-advice can override the return value by setting
ad-return-value.
The argument name is the name of the advice, a non-nil
symbol. The advice name uniquely identifies one piece of advice, within all
the pieces of advice in a particular class for a particular
function. The name allows you to refer to the piece of
advice--to redefine it, or to enable or disable it.
In place of the argument list in an ordinary definition, an advice definition calls for several different pieces of information.
The optional position specifies where, in the current list of
advice of the specified class, this new advice should be placed.
It should be either first, last or a number that specifies
a zero-based position (first is equivalent to 0). If no position
is specified, the default is first. Position values outside the
range of existing positions in this class are mapped to the beginning or
the end of the range, whichever is closer. The position value is
ignored when redefining an existing piece of advice.
The optional arglist can be used to define the argument list for the sake of advice. This becomes the argument list of the combined definition that is generated in order to run the advice (see section The Combined Definition). Therefore, the advice expressions can use the argument variables in this list to access argument values.
This argument list must be compatible with the argument list of the original function, so that it can handle the ways the function is actually called. If more than one piece of advice specifies an argument list, then the first one (the one with the smallest position) found in the list of all classes of advice is used.
The remaining elements, flags, are symbols that specify further information about how to use this piece of advice. Here are the valid symbols and their meanings:
activate
protect
unwind-protect form, so that it will execute even if the
previous code gets an error or uses throw. See section Cleaning Up from Nonlocal Exits.
compile
activate is also specified.
See section The Combined Definition.
disable
preactivate
defadvice is
compiled or macroexpanded. This generates a compiled advised definition
according to the current advice state, which will be used during
activation if appropriate.
This is useful only if this defadvice is byte-compiled.
The optional documentation-string serves to document this piece of
advice. When advice is active for function, the documentation for
function (as returned by documentation) combines the
documentation strings of all the advice for function with the
documentation string of its original function definition.
The optional interactive-form form can be supplied to change the interactive behavior of the original function. If more than one piece of advice has an interactive-form, then the first one (the one with the smallest position) found among all the advice takes precedence.
The possibly empty list of body-forms specifies the body of the advice. The body of an advice can access or change the arguments, the return value, the binding environment, and perform any other kind of side effect.
Warning: When you advise a macro, keep in mind that macros are expanded when a program is compiled, not when a compiled program is run. All subroutines used by the advice need to be available when the byte compiler expands the macro.
Around-advice lets you "wrap" a Lisp expression "around" the
original function definition. You specify where the original function
definition should go by means of the special symbol ad-do-it.
Where this symbol occurs inside the around-advice body, it is replaced
with a progn containing the forms of the surrounded code. Here
is an example:
(defadvice foo (around foo-around)
"Ignore case in `foo'."
(let ((case-fold-search t))
ad-do-it))
Its effect is to make sure that case is ignored in
searches when the original definition of foo is run.
If the around-advice does not use ad-do-it, then it does not run
the original function definition. This provides a way to override the
original definition completely. (It also overrides lower-positioned
pieces of around-advice).
The macro defadvice resembles defun in that the code for
the advice, and all other information about it, are explicitly stated in
the source code. You can also create advice whose details are computed,
using the function ad-add-advice.
ad-add-advice adds advice as a piece of advice to
function in class class. The argument advice has
this form:
(name protected enabled definition)
Here protected and enabled are flags, and definition
is the expression that says what the advice should do. If enabled
is nil, this piece of advice is initially disabled
(see section Enabling and Disabling Advice).
If function already has one or more pieces of advice in the
specified class, then position specifies where in the list
to put the new piece of advice. The value of position can either
be first, last, or a number (counting from 0 at the
beginning of the list). Numbers outside the range are mapped to the
closest extreme position.
If function already has a piece of advice with the same name, then the position argument is ignored and the old advice is replaced with the new one.
By default, advice does not take effect when you define it--only when
you activate advice for the function that was advised. You can
request the activation of advice for a function when you define the
advice, by specifying the activate flag in the defadvice.
But normally you activate the advice for a function by calling the
function ad-activate or one of the other activation commands
listed below.
Separating the activation of advice from the act of defining it permits you to add several pieces of advice to one function efficiently, without redefining the function over and over as each advice is added. More importantly, it permits defining advice for a function before that function is actually defined.
When a function's advice is first activated, the function's original definition is saved, and all enabled pieces of advice for that function are combined with the original definition to make a new definition. (Pieces of advice that are currently disabled are not used; see section Enabling and Disabling Advice.) This definition is installed, and optionally byte-compiled as well, depending on conditions described below.
In all of the commands to activate advice, if compile is t,
the command also compiles the combined definition which implements the
advice.
To activate advice for a function whose advice is already active is not a no-op. It is a useful operation which puts into effect any changes in that function's advice since the previous activation of advice for that function.
Reactivating a function's advice is useful for putting into effect all the changes that have been made in its advice (including enabling and disabling specific pieces of advice; see section Enabling and Disabling Advice) since the last time it was activated.
If the advised definition was constructed during "preactivation"
(see section Preactivation), then that definition must already be compiled,
because it was constructed during byte-compilation of the file that
contained the defadvice with the preactivate flag.
Each piece of advice has a flag that says whether it is enabled or
not. By enabling or disabling a piece of advice, you can turn it on
and off without having to undefine and redefine it. For example, here is
how to disable a particular piece of advice named my-advice for
the function foo:
(ad-disable-advice 'foo 'before 'my-advice)
This function by itself only changes the enable flag for a piece of
advice. To make the change take effect in the advised definition, you
must activate the advice for foo again:
(ad-activate 'foo)
You can also disable many pieces of advice at once, for various functions, using a regular expression. As always, the changes take real effect only when you next reactivate advice for the functions in question.
Constructing a combined definition to execute advice is moderately expensive. When a library advises many functions, this can make loading the library slow. In that case, you can use preactivation to construct suitable combined definitions in advance.
To use preactivation, specify the preactivate flag when you
define the advice with defadvice. This defadvice call
creates a combined definition which embodies this piece of advice
(whether enabled or not) plus any other currently enabled advice for the
same function, and the function's own definition. If the
defadvice is compiled, that compiles the combined definition
also.
When the function's advice is subsequently activated, if the enabled advice for the function matches what was used to make this combined definition, then the existing combined definition is used, thus avoiding the need to construct one. Thus, preactivation never causes wrong results--but it may fail to do any good, if the enabled advice at the time of activation doesn't match what was used for preactivation.
Here are some symptoms that can indicate that a preactivation did not work properly, because of a mismatch.
byte-compile is included in the value of features even
though you did not ever explicitly use the byte-compiler.
Compiled preactivated advice works properly even if the function itself is not defined until later; however, the function needs to be defined when you compile the preactivated advice.
There is no elegant way to find out why preactivated advice is not being
used. What you can do is to trace the function
ad-cache-id-verification-code (with the function
trace-function-background) before the advised function's advice
is activated. After activation, check the value returned by
ad-cache-id-verification-code for that function: verified
means that the preactivated advice was used, while other values give
some information about why they were considered inappropriate.
Warning: There is one known case that can make preactivation fail, in that a preconstructed combined definition is used even though it fails to match the current state of advice. This can happen when two packages define different pieces of advice with the same name, in the same class, for the same function. But you should avoid that anyway.
The simplest way to access the arguments of an advised function in the body of a piece of advice is to use the same names that the function definition uses. To do this, you need to know the names of the argument variables of the original function.
While this simple method is sufficient in many cases, it has a disadvantage: it is not robust, because it hard-codes the argument names into the advice. If the definition of the original function changes, the advice might break.
Another method is to specify an argument list in the advice itself. This avoids the need to know the original function definition's argument names, but it has a limitation: all the advice on any particular function must use the same argument list, because the argument list actually used for all the advice comes from the first piece of advice for that function.
A more robust method is to use macros that are translated into the proper access forms at activation time, i.e., when constructing the advised definition. Access macros access actual arguments by position regardless of how these actual arguments get distributed onto the argument variables of a function. This is robust because in Emacs Lisp the meaning of an argument is strictly determined by its position in the argument list.
Now an example. Suppose the function foo is defined as
(defun foo (x y &optional z &rest r) ...)
and is then called with
(foo 0 1 2 3 4 5 6)
which means that x is 0, y is 1, z is 2 and r is
(3 4 5 6) within the body of foo. Here is what
ad-get-arg and ad-get-args return in this case:
(ad-get-arg 0) => 0 (ad-get-arg 1) => 1 (ad-get-arg 2) => 2 (ad-get-arg 3) => 3 (ad-get-args 2) => (2 3 4 5 6) (ad-get-args 4) => (4 5 6)
Setting arguments also makes sense in this example:
(ad-set-arg 5 "five")
has the effect of changing the sixth argument to "five". If this
happens in advice executed before the body of foo is run, then
r will be (3 4 "five" 6) within that body.
Here is an example of setting a tail of the argument list:
(ad-set-args 0 '(5 4 3 2 1 0))
If this happens in advice executed before the body of foo is run,
then within that body, x will be 5, y will be 4, z
will be 3, and r will be (2 1 0) inside the body of
foo.
These argument constructs are not really implemented as Lisp macros. Instead they are implemented specially by the advice mechanism.
When the advice facility constructs the combined definition, it needs
to know the argument list of the original function. This is not always
possible for primitive functions. When advice cannot determine the
argument list, it uses (&rest ad-subr-args), which always works
but is inefficient because it constructs a list of the argument values.
You can use ad-define-subr-args to declare the proper argument
names for a primitive function:
For example,
(ad-define-subr-args 'fset '(sym newdef))
specifies the argument list for the function fset.
Suppose that a function has n pieces of before-advice, m pieces of around-advice and k pieces of after-advice. Assuming no piece of advice is protected, the combined definition produced to implement the advice for a function looks like this:
(lambda arglist
[ [advised-docstring] [(interactive ...)] ]
(let (ad-return-value)
before-0-body-form...
....
before-n-1-body-form...
around-0-body-form...
around-1-body-form...
....
around-m-1-body-form...
(setq ad-return-value
apply original definition to arglist)
other-around-m-1-body-form...
....
other-around-1-body-form...
other-around-0-body-form...
after-0-body-form...
....
after-k-1-body-form...
ad-return-value))
Macros are redefined as macros, which means adding macro to
the beginning of the combined definition.
The interactive form is present if the original function or some piece
of advice specifies one. When an interactive primitive function is
advised, a special method is used: to call the primitive with
call-interactively so that it will read its own arguments.
In this case, the advice cannot access the arguments.
The body forms of the various advice in each class are assembled according to their specified order. The forms of around-advice l are included in one of the forms of around-advice l - 1.
The innermost part of the around advice onion is
apply original definition to arglist
whose form depends on the type of the original function. The variable
ad-return-value is set to whatever this returns. The variable is
visible to all pieces of advice, which can access and modify it before
it is actually returned from the advised function.
The semantic structure of advised functions that contain protected
pieces of advice is the same. The only difference is that
unwind-protect forms ensure that the protected advice gets
executed even if some previous piece of advice had an error or a
non-local exit. If any around-advice is protected, then the whole
around-advice onion is protected as a result.
There are three ways to investigate a problem in an Emacs Lisp program, depending on what you are doing with the program when the problem appears.
Another useful debugging tool is the dribble file. When a dribble file is open, Emacs copies all keyboard input characters to that file. Afterward, you can examine the file to find out what input was used. See section Terminal Input.
For debugging problems in terminal descriptions, the
open-termscript function can be useful. See section Terminal Output.
The ordinary Lisp debugger provides the ability to suspend evaluation of a form. While evaluation is suspended (a state that is commonly known as a break), you may examine the run time stack, examine the values of local or global variables, or change those values. Since a break is a recursive edit, all the usual editing facilities of Emacs are available; you can even run programs that will enter the debugger recursively. See section Recursive Editing.
The most important time to enter the debugger is when a Lisp error happens. This allows you to investigate the immediate causes of the error.
However, entry to the debugger is not a normal consequence of an
error. Many commands frequently cause Lisp errors when invoked
inappropriately (such as C-f at the end of the buffer), and during
ordinary editing it would be very inconvenient to enter the debugger
each time this happens. So if you want errors to enter the debugger, set
the variable debug-on-error to non-nil. (The command
toggle-debug-on-error provides an easy way to do this.)
debug-on-error is t, all
kinds of errors call the debugger (except those listed in
debug-ignored-errors). If it is nil, none call the
debugger.
The value can also be a list of error conditions that should call the
debugger. For example, if you set it to the list
(void-variable), then only errors about a variable that has no
value invoke the debugger.
When this variable is non-nil, Emacs does not create an error
handler around process filter functions and sentinels. Therefore,
errors in these functions also invoke the debugger. See section Processes.
debug-on-error.
The normal value of this variable lists several errors that happen often
during editing but rarely result from bugs in Lisp programs. However,
"rarely" is not "never"; if your program fails with an error that
matches this list, you will need to change this list in order to debug
the error. The easiest way is usually to set
debug-ignored-errors to nil.
condition-case never run the
debugger, even if debug-on-error is non-nil. In other
words, condition-case gets a chance to handle the error before
the debugger gets a chance.
If you set debug-on-signal to a non-nil value, then the
debugger gets the first chance at every error; an error will invoke the
debugger regardless of any condition-case, if it fits the
criteria specified by the values of debug-on-error and
debug-ignored-errors.
Warning: This variable is strong medicine! Various parts of
Emacs handle errors in the normal course of affairs, and you may not
even realize that errors happen there. If you set
debug-on-signal to a non-nil value, those errors will
enter the debugger.
Warning: debug-on-signal has no effect when
debug-on-error is nil.
To debug an error that happens during loading of the `.emacs'
file, use the option `--debug-init', which binds
debug-on-error to t while loading `.emacs', and
bypasses the condition-case which normally catches errors in the
init file.
If your `.emacs' file sets debug-on-error, the effect may
not last past the end of loading `.emacs'. (This is an undesirable
byproduct of the code that implements the `--debug-init' command
line option.) The best way to make `.emacs' set
debug-on-error permanently is with after-init-hook, like
this:
(add-hook 'after-init-hook
'(lambda () (setq debug-on-error t)))
When a program loops infinitely and fails to return, your first problem is to stop the loop. On most operating systems, you can do this with C-g, which causes quit.
Ordinary quitting gives no information about why the program was
looping. To get more information, you can set the variable
debug-on-quit to non-nil. Quitting with C-g is not
considered an error, and debug-on-error has no effect on the
handling of C-g. Likewise, debug-on-quit has no effect on
errors.
Once you have the debugger running in the middle of the infinite loop, you can proceed from the debugger using the stepping commands. If you step through the entire loop, you will probably get enough information to solve the problem.
quit
is signaled and not handled. If debug-on-quit is non-nil,
then the debugger is called whenever you quit (that is, type C-g).
If debug-on-quit is nil, then the debugger is not called
when you quit. See section Quitting.
To investigate a problem that happens in the middle of a program, one useful technique is to enter the debugger whenever a certain function is called. You can do this to the function in which the problem occurs, and then step through the function, or you can do this to a function called shortly before the problem, step quickly over the call to that function, and then step through its caller.
(debug 'debug) into
the function definition as the first form.
Any function defined as Lisp code may be set to break on entry, regardless of whether it is interpreted code or compiled code. If the function is a command, it will enter the debugger when called from Lisp and when called interactively (after the reading of the arguments). You can't debug primitive functions (i.e., those written in C) this way.
When debug-on-entry is called interactively, it prompts for
function-name in the minibuffer. If the function is already set
up to invoke the debugger on entry, debug-on-entry does nothing.
debug-on-entry always returns function-name.
Note: if you redefine a function after using
debug-on-entry on it, the code to enter the debugger is discarded
by the redefinition. In effect, redefining the function cancels
the break-on-entry feature for that function.
(defun fact (n)
(if (zerop n) 1
(* n (fact (1- n)))))
=> fact
(debug-on-entry 'fact)
=> fact
(fact 3)
------ Buffer: *Backtrace* ------
Entering:
* fact(3)
eval-region(4870 4878 t)
byte-code("...")
eval-last-sexp(nil)
(let ...)
eval-insert-last-sexp(nil)
* call-interactively(eval-insert-last-sexp)
------ Buffer: *Backtrace* ------
(symbol-function 'fact)
=> (lambda (n)
(debug (quote debug))
(if (zerop n) 1 (* n (fact (1- n)))))
debug-on-entry on
function-name. When called interactively, it prompts for
function-name in the minibuffer. If function-name is
nil or the empty string, it cancels break-on-entry for all
functions.
Calling cancel-debug-on-entry does nothing to a function which is
not currently set up to break on entry. It always returns
function-name.
You can cause the debugger to be called at a certain point in your
program by writing the expression (debug) at that point. To do
this, visit the source file, insert the text `(debug)' at the
proper place, and type C-M-x. Warning: if you do this
for temporary debugging purposes, be sure to undo this insertion before
you save the file!
The place where you insert `(debug)' must be a place where an
additional form can be evaluated and its value ignored. (If the value
of (debug) isn't ignored, it will alter the execution of the
program!) The most common suitable places are inside a progn or
an implicit progn (see section Sequencing).
When the debugger is entered, it displays the previously selected buffer in one window and a buffer named `*Backtrace*' in another window. The backtrace buffer contains one line for each level of Lisp function execution currently going on. At the beginning of this buffer is a message describing the reason that the debugger was invoked (such as the error message and associated data, if it was invoked due to an error).
The backtrace buffer is read-only and uses a special major mode, Debugger mode, in which letters are defined as debugger commands. The usual Emacs editing commands are available; thus, you can switch windows to examine the buffer that was being edited at the time of the error, switch buffers, visit files, or do any other sort of editing. However, the debugger is a recursive editing level (see section Recursive Editing) and it is wise to go back to the backtrace buffer and exit the debugger (with the q command) when you are finished with it. Exiting the debugger gets out of the recursive edit and kills the backtrace buffer.
The backtrace buffer shows you the functions that are executing and their argument values. It also allows you to specify a stack frame by moving point to the line describing that frame. (A stack frame is the place where the Lisp interpreter records information about a particular invocation of a function.) The frame whose line point is on is considered the current frame. Some of the debugger commands operate on the current frame.
The debugger itself must be run byte-compiled, since it makes assumptions about how many stack frames are used for the debugger itself. These assumptions are false if the debugger is running interpreted.
Inside the debugger (in Debugger mode), these special commands are available in addition to the usual cursor motion commands. (Keep in mind that all the usual facilities of Emacs, such as switching windows or buffers, are still available.)
The most important use of debugger commands is for stepping through code, so that you can see how control flows. The debugger can step through the control structures of an interpreted function, but cannot do so in a byte-compiled function. If you would like to step through a byte-compiled function, replace it with an interpreted definition of the same function. (To do this, visit the source for the function and type C-M-x on its definition.)
Here is a list of Debugger mode commands:
debug and use its return value. Otherwise, r has the same
effect as c, and the specified return value does not matter.
You can't use r when the debugger was entered due to an error.
Here we describe in full detail the function debug that is used
to invoke the debugger.
The Debugger mode c and r commands exit the recursive edit;
then debug switches back to the previous buffer and returns to
whatever called debug. This is the only way the function
debug can return to its caller.
The use of the debugger-args is that debug displays the
rest of its arguments at the top of the `*Backtrace*' buffer, so
that the user can see them. Except as described below, this is the
only way these arguments are used.
However, certain values for first argument to debug have a
special significance. (Normally, these values are used only by the
internals of Emacs, and not by programmers calling debug.) Here
is a table of these special values:
lambda
lambda means debug was called because
of entry to a function when debug-on-next-call was
non-nil. The debugger displays `Entering:' as a line of
text at the top of the buffer.
debug
debug as first argument indicates a call to debug because
of entry to a function that was set to debug on entry. The debugger
displays `Entering:', just as in the lambda case. It also
marks the stack frame for that function so that it will invoke the
debugger when exited.
t
t, this indicates a call to
debug due to evaluation of a list form when
debug-on-next-call is non-nil. The debugger displays the
following as the top line in the buffer:
Beginning evaluation of function call form:
exit
exit, it indicates the exit of a stack
frame previously marked to invoke the debugger on exit. The second
argument given to debug in this case is the value being returned
from the frame. The debugger displays `Return value:' in the top
line of the buffer, followed by the value being returned.
error
error, the debugger indicates that
it is being entered because an error or quit was signaled and not
handled, by displaying `Signaling:' followed by the error signaled
and any arguments to signal. For example,
(let ((debug-on-error t)) (/ 1 0)) ------ Buffer: *Backtrace* ------ Signaling: (arith-error) /(1 0) ... ------ Buffer: *Backtrace* ------If an error was signaled, presumably the variable
debug-on-error is non-nil. If quit was signaled,
then presumably the variable debug-on-quit is non-nil.
nil
nil as the first of the debugger-args when you want
to enter the debugger explicitly. The rest of the debugger-args
are printed on the top line of the buffer. You can use this feature to
display messages--for example, to remind yourself of the conditions
under which debug is called.
This section describes functions and variables used internally by the debugger.
debug.
The first argument that Lisp hands to the function indicates why it
was called. The convention for arguments is detailed in the description
of debug.
debug to fill up the
`*Backtrace*' buffer. It is written in C, since it must have access
to the stack to determine which function calls are active. The return
value is always nil.
In the following example, a Lisp expression calls backtrace
explicitly. This prints the backtrace to the stream
standard-output: in this case, to the buffer
`backtrace-output'. Each line of the backtrace represents one
function call. The line shows the values of the function's arguments if
they are all known. If they are still being computed, the line says so.
The arguments of special forms are elided.
(with-output-to-temp-buffer "backtrace-output"
(let ((var 1))
(save-excursion
(setq var (eval '(progn
(1+ var)
(list 'testing (backtrace))))))))
=> nil
----------- Buffer: backtrace-output ------------
backtrace()
(list ...computing arguments...)
(progn ...)
eval((progn (1+ var) (list (quote testing) (backtrace))))
(setq ...)
(save-excursion ...)
(let ...)
(with-output-to-temp-buffer ...)
eval-region(1973 2142 #<buffer *scratch*>)
byte-code("... for eval-print-last-sexp ...")
eval-print-last-sexp(nil)
* call-interactively(eval-print-last-sexp)
----------- Buffer: backtrace-output ------------
The character `*' indicates a frame whose debug-on-exit flag is set.
nil, it says to call the debugger before
the next eval, apply or funcall. Entering the
debugger sets debug-on-next-call to nil.
The d command in the debugger works by setting this variable.
nil, this will cause the debugger to be entered when that
frame later exits. Even a nonlocal exit through that frame will enter
the debugger.
This function is used only by the debugger.
nil. The debugger can set this variable to leave
information for future debugger invocations during the same command
invocation.
The advantage, for the debugger, of using this variable rather than an ordinary global variable is that the data will never carry over to a subsequent command invocation.
backtrace-frame is intended for use in Lisp
debuggers. It returns information about what computation is happening
in the stack frame frame-number levels down.
If that frame has not evaluated the arguments yet (or is a special
form), the value is (nil function arg-forms...).
If that frame has evaluated its arguments and called its function
already, the value is (t function
arg-values...).
In the return value, function is whatever was supplied as the
CAR of the evaluated list, or a lambda expression in the
case of a macro call. If the function has a &rest argument, that
is represented as the tail of the list arg-values.
If frame-number is out of range, backtrace-frame returns
nil.
Edebug is a source-level debugger for Emacs Lisp programs with which you can:
The first three sections below should tell you enough about Edebug to enable you to use it.
To debug a Lisp program with Edebug, you must first instrument
the Lisp code that you want to debug. A simple way to do this is to
first move point into the definition of a function or macro and then do
C-u C-M-x (eval-defun with a prefix argument). See
section Instrumenting for Edebug, for alternative ways to instrument code.
Once a function is instrumented, any call to the function activates Edebug. Activating Edebug may stop execution and let you step through the function, or it may update the display and continue execution while checking for debugging commands, depending on which Edebug execution mode you have selected. The default execution mode is step, which does stop execution. See section Edebug Execution Modes.
Within Edebug, you normally view an Emacs buffer showing the source of the Lisp code you are debugging. This is referred to as the source code buffer. This buffer is temporarily read-only.
An arrow at the left margin indicates the line where the function is executing. Point initially shows where within the line the function is executing, but this ceases to be true if you move point yourself.
If you instrument the definition of fac (shown below) and then
execute (fac 3), here is what you normally see. Point is at the
open-parenthesis before if.
(defun fac (n)
=>-!-(if (< 0 n)
(* n (fac (1- n)))
1))
The places within a function where Edebug can stop execution are called
stop points. These occur both before and after each subexpression
that is a list, and also after each variable reference.
Here we show with periods the stop points found in the function
fac:
(defun fac (n)
.(if .(< 0 n.).
.(* n. .(fac (1- n.).).).
1).)
The special commands of Edebug are available in the source code buffer
in addition to the commands of Emacs Lisp mode. For example, you can
type the Edebug command SPC to execute until the next stop point.
If you type SPC once after entry to fac, here is the
display you will see:
(defun fac (n)
=>(if -!-(< 0 n)
(* n (fac (1- n)))
1))
When Edebug stops execution after an expression, it displays the expression's value in the echo area.
Other frequently used commands are b to set a breakpoint at a stop point, g to execute until a breakpoint is reached, and q to exit Edebug and return to the top-level command loop. Type ? to display a list of all Edebug commands.
In order to use Edebug to debug Lisp code, you must first instrument the code. Instrumenting code inserts additional code into it, to invoke Edebug at the proper places.
Once you have loaded Edebug, the command C-M-x
(eval-defun) is redefined so that when invoked with a prefix
argument on a definition, it instruments the definition before
evaluating it. (The source code itself is not modified.) If the
variable edebug-all-defs is non-nil, that inverts the
meaning of the prefix argument: then C-M-x instruments the
definition unless it has a prefix argument. The default value of
edebug-all-defs is nil. The command M-x
edebug-all-defs toggles the value of the variable
edebug-all-defs.
If edebug-all-defs is non-nil, then the commands
eval-region, eval-current-buffer, and eval-buffer
also instrument any definitions they evaluate. Similarly,
edebug-all-forms controls whether eval-region should
instrument any form, even non-defining forms. This doesn't apply
to loading or evaluations in the minibuffer. The command M-x
edebug-all-forms toggles this option.
Another command, M-x edebug-eval-top-level-form, is available to
instrument any top-level form regardless of the values of
edebug-all-defs and edebug-all-forms.
While Edebug is active, the command I
(edebug-instrument-callee) instruments the definition of the
function or macro called by the list form after point, if is not already
instrumented. This is possible only if Edebug knows where to find the
source for that function; after loading Edebug, eval-region
records the position of every definition it evaluates, even if not
instrumenting it. See also the i command (see section Jumping), which
steps into the call after instrumenting the function.
Edebug knows how to instrument all the standard special forms,
interactive forms with an expression argument, anonymous lambda
expressions, and other defining forms. Edebug cannot know what a
user-defined macro will do with the arguments of a macro call, so you
must tell it; see section Instrumenting Macro Calls, for details.
When Edebug is about to instrument code for the first time in a
session, it runs the hook edebug-setup-hook, then sets it to
nil. You can use this to arrange to load Edebug specifications
(see section Instrumenting Macro Calls) associated with a package you are
using, but actually load them only if you use Edebug.
To remove instrumentation from a definition, simply re-evaluate its
definition in a way that does not instrument. There are two ways of
evaluating forms that never instrument them: from a file with
load, and from the minibuffer with eval-expression
(M-:).
If Edebug detects a syntax error while instrumenting, it leaves point
at the erroneous code and signals an invalid-read-syntax error.
See section Evaluation, for other evaluation functions available inside of Edebug.
Edebug supports several execution modes for running the program you are debugging. We call these alternatives Edebug execution modes; do not confuse them with major or minor modes. The current Edebug execution mode determines how far Edebug continues execution before stopping--whether it stops at each stop point, or continues to the next breakpoint, for example--and how much Edebug displays the progress of the evaluation before it stops.
Normally, you specify the Edebug execution mode by typing a command to continue the program in a certain mode. Here is a table of these commands. All except for S resume execution of the program, at least for a certain distance.
edebug-stop).
edebug-step-mode).
edebug-next-mode). Also see edebug-forward-sexp in
section Miscellaneous Edebug Commands.
edebug-trace-mode).
edebug-Trace-fast-mode).
edebug-go-mode). See section Breakpoints.
edebug-continue-mode).
edebug-Continue-fast-mode).
edebug-Go-nonstop-mode). You
can still stop the program by typing S, or any editing command.
In general, the execution modes earlier in the above list run the program more slowly or stop sooner than the modes later in the list.
While executing or tracing, you can interrupt the execution by typing any Edebug command. Edebug stops the program at the next stop point and then executes the command you typed. For example, typing t during execution switches to trace mode at the next stop point. You can use S to stop execution without doing anything else.
If your function happens to read input, a character you type intending to interrupt execution may be read by the function instead. You can avoid such unintended results by paying attention to when your program wants input.
Keyboard macros containing the commands in this section do not
completely work: exiting from Edebug, to resume the program, loses track
of the keyboard macro. This is not easy to fix. Also, defining or
executing a keyboard macro outside of Edebug does not affect commands
inside Edebug. This is usually an advantage. But see the
edebug-continue-kbd-macro option (see section Edebug Options).
When you enter a new Edebug level, the initial execution mode comes from
the value of the variable edebug-initial-mode. By default, this
specifies step mode. Note that you may reenter the same Edebug level
several times if, for example, an instrumented function is called
several times from one command.
The commands described in this section execute until they reach a specified location. All except i make a temporary breakpoint to establish the place to stop, then switch to go mode. Any other breakpoint reached before the intended stop point will also stop execution. See section Breakpoints, for the details on breakpoints.
These commands may fail to work as expected in case of nonlocal exit, because a nonlocal exit can bypass the temporary breakpoint where you expected the program to stop.
edebug-goto-here).
edebug-forward-sexp).
The h command proceeds to the stop point near the current location of point, using a temporary breakpoint. See section Breakpoints, for more information about breakpoints.
The f command runs the program forward over one expression. More precisely, it sets a temporary breakpoint at the position that C-M-f would reach, then executes in go mode so that the program will stop at breakpoints.
With a prefix argument n, the temporary breakpoint is placed n sexps beyond point. If the containing list ends before n more elements, then the place to stop is after the containing expression.
Be careful that the position C-M-f finds is a place that the
program will really get to; this may not be true in a
cond, for example.
The f command does forward-sexp starting at point, rather
than at the stop point, for flexibility. If you want to execute one
expression from the current stop point, type w first, to
move point there, and then type f.
The o command continues "out of" an expression. It places a temporary breakpoint at the end of the sexp containing point. If the containing sexp is a function definition itself, o continues until just before the last sexp in the definition. If that is where you are now, it returns from the function and then stops. In other words, this command does not exit the currently executing function unless you are positioned after the last sexp.
The i command steps into the function or macro called by the list form after point, and stops at its first stop point. Note that the form need not be the one about to be evaluated. But if the form is a function call about to be evaluated, remember to use this command before any of the arguments are evaluated, since otherwise it will be too late.
The i command instruments the function or macro it's supposed to step into, if it isn't instrumented already. This is convenient, but keep in mind that the function or macro remains instrumented unless you explicitly arrange to deinstrument it.
Some miscellaneous Edebug commands are described here.
edebug-help).
abort-recursive-edit).
top-level). This
exits all recursive editing levels, including all levels of Edebug
activity. However, instrumented code protected with
unwind-protect or condition-case forms may resume
debugging.
top-level-nonstop).
edebug-previous-result).
edebug-backtrace).
You cannot use debugger commands in the backtrace buffer in Edebug as
you would in the standard debugger.
The backtrace buffer is killed automatically when you continue
execution.
From the Edebug recursive edit, you may invoke commands that activate Edebug again recursively. Any time Edebug is active, you can quit to the top level with q or abort one recursive edit level with C-]. You can display a backtrace of all the pending evaluations with d.
Edebug's step mode stops execution at the next stop point reached. There are three other ways to stop Edebug execution once it has started: breakpoints, the global break condition, and source breakpoints.
While using Edebug, you can specify breakpoints in the program you are testing: points where execution should stop. You can set a breakpoint at any stop point, as defined in section Using Edebug. For setting and unsetting breakpoints, the stop point that is affected is the first one at or after point in the source code buffer. Here are the Edebug commands for breakpoints:
edebug-set-breakpoint). If you use a prefix argument, the
breakpoint is temporary (it turns off the first time it stops the
program).
edebug-unset-breakpoint).
nil value
(edebug-set-conditional-breakpoint). With a prefix argument, the
breakpoint is temporary.
edebug-next-breakpoint).
While in Edebug, you can set a breakpoint with b and unset one with u. First move point to the Edebug stop point of your choice, then type b or u to set or unset a breakpoint there. Unsetting a breakpoint where none has been set has no effect.
Re-evaluating or reinstrumenting a definition forgets all its breakpoints.
A conditional breakpoint tests a condition each time the program
gets there. Any errors that occur as a result of evaluating the
condition are ignored, as if the result were nil. To set a
conditional breakpoint, use x, and specify the condition
expression in the minibuffer. Setting a conditional breakpoint at a
stop point that has a previously established conditional breakpoint puts
the previous condition expression in the minibuffer so you can edit it.
You can make a conditional or unconditional breakpoint temporary by using a prefix argument with the command to set the breakpoint. When a temporary breakpoint stops the program, it is automatically unset.
Edebug always stops or pauses at a breakpoint except when the Edebug mode is Go-nonstop. In that mode, it ignores breakpoints entirely.
To find out where your breakpoints are, use the B command, which moves point to the next breakpoint following point, within the same function, or to the first breakpoint if there are no following breakpoints. This command does not continue execution--it just moves point in the buffer.
A global break condition stops execution when a specified
condition is satisfied, no matter where that may occur. Edebug
evaluates the global break condition at every stop point. If it
evaluates to a non-nil value, then execution stops or pauses
depending on the execution mode, as if a breakpoint had been hit. If
evaluating the condition gets an error, execution does not stop.
The condition expression is stored in
edebug-global-break-condition. You can specify a new expression
using the X command (edebug-set-global-break-condition).
The global break condition is the simplest way to find where in your
code some event occurs, but it makes code run much more slowly. So you
should reset the condition to nil when not using it.
All breakpoints in a definition are forgotten each time you
reinstrument it. To make a breakpoint that won't be forgotten, you can
write a source breakpoint, which is simply a call to the function
edebug in your source code. You can, of course, make such a call
conditional. For example, in the fac function, insert the first
line as shown below to stop when the argument reaches zero:
(defun fac (n)
(if (= n 0) (edebug))
(if (< 0 n)
(* n (fac (1- n)))
1))
When the fac definition is instrumented and the function is
called, the call to edebug acts as a breakpoint. Depending on
the execution mode, Edebug stops or pauses there.
If no instrumented code is being executed when edebug is called,
that function calls debug.
Emacs normally displays an error message when an error is signaled and
not handled with condition-case. While Edebug is active and
executing instrumented code, it normally responds to all unhandled
errors. You can customize this with the options edebug-on-error
and edebug-on-quit; see section Edebug Options.
When Edebug responds to an error, it shows the last stop point encountered before the error. This may be the location of a call to a function which was not instrumented, within which the error actually occurred. For an unbound variable error, the last known stop point might be quite distant from the offending variable reference. In that case you might want to display a full backtrace (see section Miscellaneous Edebug Commands).
If you change debug-on-error or debug-on-quit while
Edebug is active, these changes will be forgotten when Edebug becomes
inactive. Furthermore, during Edebug's recursive edit, these variables
are bound to the values they had outside of Edebug.
These Edebug commands let you view aspects of the buffer and window status as they were before entry to Edebug. The outside window configuration is the collection of windows and contents that were in effect outside of Edebug.
edebug-view-outside).
edebug-bounce-point). With a prefix argument n,
pause for n seconds instead.
edebug-where).
If you use this command in a different window displaying the same
buffer, that window will be used instead to display the current
definition in the future.
edebug-toggle-save-windows).
With a prefix argument, W only toggles saving and restoring of
the selected window. To specify a window that is not displaying the
source code buffer, you must use C-x X W from the global keymap.
You can view the outside window configuration with v or just bounce to the point in the current buffer with p, even if it is not normally displayed. After moving point, you may wish to jump back to the stop point with w from a source code buffer.
Each time you use W to turn saving off, Edebug forgets the saved outside window configuration--so that even if you turn saving back on, the current window configuration remains unchanged when you next exit Edebug (by continuing the program). However, the automatic redisplay of `*edebug*' and `*edebug-trace*' may conflict with the buffers you wish to see unless you have enough windows open.
While within Edebug, you can evaluate expressions "as if" Edebug were not running. Edebug tries to be invisible to the expression's evaluation and printing. Evaluation of expressions that cause side effects will work as expected except for things that Edebug explicitly saves and restores. See section The Outside Context, for details on this process.
edebug-eval-expression). That is, Edebug tries to minimize its
interference with the evaluation.
edebug-eval-last-sexp).
Edebug supports evaluation of expressions containing references to
lexically bound symbols created by the following constructs in
`cl.el' (version 2.03 or later): lexical-let,
macrolet, and symbol-macrolet.
You can use the evaluation list buffer, called `*edebug*', to evaluate expressions interactively. You can also set up the evaluation list of expressions to be evaluated automatically each time Edebug updates the display.
edebug-visit-eval-list).
In the `*edebug*' buffer you can use the commands of Lisp Interaction mode (see section `Lisp Interaction' in The GNU Emacs Manual) as well as these special commands:
edebug-eval-print-last-sexp).
edebug-eval-last-sexp).
edebug-update-eval-list).
edebug-delete-eval-item).
edebug-where).
You can evaluate expressions in the evaluation list window with C-j or C-x C-e, just as you would in `*scratch*'; but they are evaluated in the context outside of Edebug.
The expressions you enter interactively (and their results) are lost when you continue execution; but you can set up an evaluation list consisting of expressions to be evaluated each time execution stops.
To do this, write one or more evaluation list groups in the evaluation list buffer. An evaluation list group consists of one or more Lisp expressions. Groups are separated by comment lines.
The command C-c C-u (edebug-update-eval-list) rebuilds the
evaluation list, scanning the buffer and using the first expression of
each group. (The idea is that the second expression of the group is the
value previously computed and displayed.)
Each entry to Edebug redisplays the evaluation list by inserting each expression in the buffer, followed by its current value. It also inserts comment lines so that each expression becomes its own group. Thus, if you type C-c C-u again without changing the buffer text, the evaluation list is effectively unchanged.
If an error occurs during an evaluation from the evaluation list, the error message is displayed in a string as if it were the result. Therefore, expressions that use variables not currently valid do not interrupt your debugging.
Here is an example of what the evaluation list window looks like after several expressions have been added to it:
(current-buffer) #<buffer *scratch*> ;--------------------------------------------------------------- (selected-window) #<window 16 on *scratch*> ;--------------------------------------------------------------- (point) 196 ;--------------------------------------------------------------- bad-var "Symbol's value as variable is void: bad-var" ;--------------------------------------------------------------- (recursion-depth) 0 ;--------------------------------------------------------------- this-command eval-last-sexp ;---------------------------------------------------------------
To delete a group, move point into it and type C-c C-d, or simply delete the text for the group and update the evaluation list with C-c C-u. To add a new expression to the evaluation list, insert the expression at a suitable place, and insert a new comment line. (You need not insert dashes in the comment line--its contents don't matter.) Then type C-c C-u.
After selecting `*edebug*', you can return to the source code buffer with C-c C-w. The `*edebug*' buffer is killed when you continue execution, and recreated next time it is needed.
If an expression in your program produces a value containing circular list structure, you may get an error when Edebug attempts to print it.
One way to cope with circular structure is to set print-length
or print-level to truncate the printing. Edebug does this for
you; it binds print-length and print-level to 50 if they
were nil. (Actually, the variables edebug-print-length
and edebug-print-level specify the values to use within Edebug.)
See section Variables Affecting Output.
nil, bind print-length to this while printing
results in Edebug. The default value is 50.
nil, bind print-level to this while printing
results in Edebug. The default value is 50.
You can also print circular structures and structures that share elements more informatively by using the `cust-print' package.
To load `cust-print' and activate custom printing only for Edebug, simply use the command M-x edebug-install-custom-print. To restore the standard print functions, use M-x edebug-uninstall-custom-print.
Here is an example of code that creates a circular structure:
(setq a '(x y)) (setcar a a)
Custom printing prints this as `Result: #1=(#1# y)'. The `#1=' notation labels the structure that follows it with the label `1', and the `#1#' notation references the previously labeled structure. This notation is used for any shared elements of lists or vectors.
nil, bind print-circle to this while printing
results in Edebug. The default value is nil.
Other programs can also use custom printing; see `cust-print.el' for details.
Edebug can record an execution trace, storing it in a buffer named
`*edebug-trace*'. This is a log of function calls and returns,
showing the function names and their arguments and values. To enable
trace recording, set edebug-trace to a non-nil value.
Making a trace buffer is not the same thing as using trace execution mode (see section Edebug Execution Modes).
When trace recording is enabled, each function entry and exit adds lines to the trace buffer. A function entry record looks like `::::{' followed by the function name and argument values. A function exit record looks like `::::}' followed by the function name and result of the function.
The number of `:'s in an entry shows its recursion depth. You can use the braces in the trace buffer to find the matching beginning or end of function calls.
You can customize trace recording for function entry and exit by
redefining the functions edebug-print-trace-before and
edebug-print-trace-after.
edebug-tracing returns the value of the last form in body.
(apply 'format format-string format-args).
It also appends a newline to separate entries.
edebug-tracing and edebug-trace insert lines in the
trace buffer whenever they are called, even if Edebug is not active.
Adding text to the trace buffer also scrolls its window to show the last
lines inserted.
Edebug provides rudimentary coverage testing and display of execution frequency.
Coverage testing works by comparing the result of each expression with the previous result; each form in the program is considered "covered" if it has returned two different values since you began testing coverage in the current Emacs session. Thus, to do coverage testing on your program, execute it under various conditions and note whether it behaves correctly; Edebug will tell you when you have tried enough different conditions that each form has returned two different values.
Coverage testing makes execution slower, so it is only done if
edebug-test-coverage is non-nil. Frequency counting is
performed for all execution of an instrumented function, even if the
execution mode is Go-nonstop, and regardless of whether coverage testing
is enabled.
Use M-x edebug-display-freq-count to display both the coverage information and the frequency counts for a definition.
The frequency counts appear as comment lines after each line of code,
and you can undo all insertions with one undo command. The
counts appear under the `(' before an expression or the `)'
after an expression, or on the last character of a variable. To
simplify the display, a count is not shown if it is equal to the
count of an earlier expression on the same line.
The character `=' following the count for an expression says that the expression has returned the same value each time it was evaluated. In other words, it is not yet "covered" for coverage testing purposes.
To clear the frequency count and coverage data for a definition,
simply reinstrument it with eval-defun.
For example, after evaluating (fac 5) with a source
breakpoint, and setting edebug-test-coverage to t, when
the breakpoint is reached, the frequency data looks like this:
(defun fac (n)
(if (= n 0) (edebug))
;#6 1 0 =5
(if (< 0 n)
;#5 =
(* n (fac (1- n)))
;# 5 0
1))
;# 0
The comment lines show that fac was called 6 times. The
first if statement returned 5 times with the same result each
time; the same is true of the condition on the second if.
The recursive call of fac did not return at all.
Edebug tries to be transparent to the program you are debugging, but it does not succeed completely. Edebug also tries to be transparent when you evaluate expressions with e or with the evaluation list buffer, by temporarily restoring the outside context. This section explains precisely what context Edebug restores, and how Edebug fails to be completely transparent.
Whenever Edebug is entered, it needs to save and restore certain data before even deciding whether to make trace information or stop the program.
max-lisp-eval-depth and max-specpdl-size are both
incremented once to reduce Edebug's impact on the stack. You could,
however, still run out of stack space when using Edebug.
executing-macro is bound to
edebug-continue-kbd-macro.
When Edebug needs to display something (e.g., in trace mode), it saves the current window configuration from "outside" Edebug (see section Window Configurations). When you exit Edebug (by continuing the program), it restores the previous window configuration.
Emacs redisplays only when it pauses. Usually, when you continue execution, the program comes back into Edebug at a breakpoint or after stepping without pausing or reading input in between. In such cases, Emacs never gets a chance to redisplay the "outside" configuration. What you see is the same window configuration as the last time Edebug was active, with no interruption.
Entry to Edebug for displaying something also saves and restores the following data, but some of these are deliberately not restored if an error or quit signal occurs.
edebug-save-windows is non-nil (see section Edebug Display Update).
The window configuration is not restored on error or quit, but the
outside selected window is reselected even on error or quit in
case a save-excursion is active. If the value of
edebug-save-windows is a list, only the listed windows are saved
and restored.
The window start and horizontal scrolling of the source code buffer are
not restored, however, so that the display remains coherent within Edebug.
edebug-save-displayed-buffer-points is non-nil.
overlay-arrow-position and
overlay-arrow-string are saved and restored. So you can safely
invoke Edebug from the recursive edit elsewhere in the same buffer.
cursor-in-echo-area is locally bound to nil so that
the cursor shows up in the window.
When Edebug is entered and actually reads commands from the user, it saves (and later restores) these additional data:
last-command, this-command, last-command-char,
last-input-char, last-input-event,
last-command-event, last-event-frame,
last-nonmenu-event, and track-mouse. Commands used within
Edebug do not affect these variables outside of Edebug.
The key sequence returned by this-command-keys is changed by
executing commands within Edebug and there is no way to reset
the key sequence from Lisp.
Edebug cannot save and restore the value of
unread-command-events. Entering Edebug while this variable has a
nontrivial value can interfere with execution of the program you are
debugging.
command-history. In rare cases this can alter execution.
standard-output and standard-input are bound to nil
by the recursive-edit, but Edebug temporarily restores them during
evaluations.
defining-kbd-macro is bound to
edebug-continue-kbd-macro.
When Edebug instruments an expression that calls a Lisp macro, it needs additional information about the macro to do the job properly. This is because there is no a-priori way to tell which subexpressions of the macro call are forms to be evaluated. (Evaluation may occur explicitly in the macro body, or when the resulting expansion is evaluated, or any time later.)
Therefore, you must define an Edebug specification for each macro that
Edebug will encounter, to explain the format of calls to that macro. To
do this, use def-edebug-spec.
The macro argument can actually be any symbol, not just a macro name.
Here is a simple example that defines the specification for the
for example macro (see section Evaluating Macro Arguments Repeatedly), followed by an
alternative, equivalent specification.
(def-edebug-spec for (symbolp "from" form "to" form "do" &rest form)) (def-edebug-spec for (symbolp ['from form] ['to form] ['do body]))
Here is a table of the possibilities for specification and how each directs processing of arguments.
t
0
A specification list is required for an Edebug specification if
some arguments of a macro call are evaluated while others are not. Some
elements in a specification list match one or more arguments, but others
modify the processing of all following elements. The latter, called
specification keywords, are symbols beginning with `&' (such
as &optional).
A specification list may contain sublists which match arguments that are themselves lists, or it may contain vectors used for grouping. Sublists and groups thus subdivide the specification list into a hierarchy of levels. Specification keywords apply only to the remainder of the sublist or group they are contained in.
When a specification list involves alternatives or repetition, matching it against an actual macro call may require backtracking. See section Backtracking in Specifications, for more details.
Edebug specifications provide the power of regular expression matching, plus some context-free grammar constructs: the matching of sublists with balanced parentheses, recursive processing of forms, and recursion via indirect specifications.
Here's a table of the possible elements of a specification list, with their meanings:
sexp
form
place
setf construct.
body
&rest form. See &rest below.
function-form
quote rather than
function, since it instruments the body of the lambda expression
either way.
lambda-expr
&optional
[&optional specs...]. To specify that several
elements must all match or none, use &optional
[specs...]. See the defun example below.
&rest
[&rest specs...].
To specify several elements that must all match on every repetition, use
&rest [specs...].
&or
&or
specification fails.
Each list element following &or is a single alternative. To
group two or more list elements as a single alternative, enclose them in
[...].
¬
&or, but if any of them match, the specification fails. If none
of them match, nothing is matched, but the ¬ specification
succeeds.
&define
&define keyword should be the first element in
a list specification.
nil
gate
let example
below.
other-symbol
def-edebug-spec
just as for macros. See the defun example below.
Otherwise, the symbol should be a predicate. The predicate is called
with the argument and the specification fails if the predicate returns
nil. In either case, that argument is not instrumented.
Some suitable predicates include symbolp, integerp,
stringp, vectorp, and atom.
[elements...]
"string"
'symbol, where the name
of symbol is the string, but the string form is preferred.
(vector elements...)
(elements...)
(spec . [(more
specs...)])) whose elements match the non-dotted list arguments.
This is useful in recursive specifications such as in the backquote
example below. Also see the description of a nil specification
above for terminating such recursion.
Note that a sublist specification written as (specs . nil)
is equivalent to (specs), and (specs .
(sublist-elements...)) is equivalent to (specs
sublist-elements...).
Here is a list of additional specifications that may appear only after
&define. See the defun example below.
name
:name
:name should be a symbol; it is used as an additional
name component for the definition. You can use this to add a unique,
static component to the name of the definition. It may be used more
than once.
arg
lambda-list
def-body
body, described above, but a definition body must be instrumented
with a different Edebug call that looks up information associated with
the definition. Use def-body for the highest level list of forms
within the definition.
def-form
def-body, except use this to match a single form rather than
a list of forms. As a special case, def-form also means that
tracing information is not output when the form is executed. See the
interactive example below.
If a specification fails to match at some point, this does not
necessarily mean a syntax error will be signaled; instead,
backtracking will take place until all alternatives have been
exhausted. Eventually every element of the argument list must be
matched by some element in the specification, and every required element
in the specification must match some argument.
When a syntax error is detected, it might not be reported until much
later after higher-level alternatives have been exhausted, and with the
point positioned further from the real error. But if backtracking is
disabled when an error occurs, it can be reported immediately. Note
that backtracking is also reenabled automatically in several situations;
it is reenabled when a new alternative is established by
&optional, &rest, or &or, or at the start of
processing a sublist, group, or indirect specification. The effect of
enabling or disabling backtracking is limited to the remainder of the
level currently being processed and lower levels.
Backtracking is disabled while matching any of the
form specifications (that is, form, body, def-form, and
def-body). These specifications will match any form so any error
must be in the form itself rather than at a higher level.
Backtracking is also disabled after successfully matching a quoted
symbol or string specification, since this usually indicates a
recognized construct. But if you have a set of alternative constructs that
all begin with the same symbol, you can usually work around this
constraint by factoring the symbol out of the alternatives, e.g.,
["foo" &or [first case] [second case] ...].
Most needs are satisfied by these two ways that bactracking is
automatically disabled, but occasionally it is useful to explicitly
disable backtracking by using the gate specification. This is
useful when you know that no higher alternatives could apply. See the
example of the let specification.
It may be easier to understand Edebug specifications by studying the examples provided here.
A let special form has a sequence of bindings and a body. Each
of the bindings is either a symbol or a sublist with a symbol and
optional expression. In the specification below, notice the gate
inside of the sublist to prevent backtracking once a sublist is found.
(def-edebug-spec let
((&rest
&or symbolp (gate symbolp &optional form))
body))
Edebug uses the following specifications for defun and
defmacro and the associated argument list and interactive
specifications. It is necessary to handle interactive forms specially
since an expression argument it is actually evaluated outside of the
function body.
(def-edebug-spec defmacro defun) ; Indirect ref todefunspec. (def-edebug-spec defun (&define name lambda-list [&optional stringp] ; Match the doc string, if present. [&optional ("interactive" interactive)] def-body)) (def-edebug-spec lambda-list (([&rest arg] [&optional ["&optional" arg &rest arg]] &optional ["&rest" arg] ))) (def-edebug-spec interactive (&optional &or stringp def-form)) ; Notice:def-form
The specification for backquote below illustrates how to match
dotted lists and use nil to terminate recursion. It also
illustrates how components of a vector may be matched. (The actual
specification defined by Edebug does not support dotted lists because
doing so causes very deep recursion that could fail.)
(def-edebug-spec ` (backquote-form)) ; Alias just for clarity.
(def-edebug-spec backquote-form
(&or ([&or "," ",@"] &or ("quote" backquote-form) form)
(backquote-form . [&or nil backquote-form])
(vector &rest backquote-form)
sexp))
These options affect the behavior of Edebug:
edebug-setup-hook is reset to nil. You could use this to
load up Edebug specifications associated with a package you are using
but only when you also use Edebug.
See section Instrumenting for Edebug.
nil, normal evaluation of defining forms such as
defun and defmacro instruments them for Edebug. This
applies to eval-defun, eval-region, eval-buffer,
and eval-current-buffer.
Use the command M-x edebug-all-defs to toggle the value of this option. See section Instrumenting for Edebug.
nil, the commands eval-defun,
eval-region, eval-buffer, and eval-current-buffer
instrument all forms, even those that don't define anything.
This doesn't apply to loading or evaluations in the minibuffer.
Use the command M-x edebug-all-forms to toggle the value of this option. See section Instrumenting for Edebug.
nil, Edebug saves and restores the window
configuration. That takes some time, so if your program does not care
what happens to the window configurations, it is better to set this
variable to nil.
If the value is a list, only the listed windows are saved and restored.
You can use the W command in Edebug to change this variable interactively. See section Edebug Display Update.
nil, Edebug saves and restores point in all
displayed buffers.
Saving and restoring point in other buffers is necessary if you are debugging code that changes the point of a buffer which is displayed in a non-selected window. If Edebug or the user then selects the window, point in that buffer will move to the window's value of point.
Saving and restoring point in all buffers is expensive, since it requires selecting each window twice, so enable this only if you need it. See section Edebug Display Update.
nil, it specifies the initial execution
mode for Edebug when it is first activated. Possible values are
step, next, go, Go-nonstop, trace,
Trace-fast, continue, and Continue-fast.
The default value is step.
See section Edebug Execution Modes.
nil means display a trace of function entry and exit.
Tracing output is displayed in a buffer named `*edebug-trace*', one
function entry or exit per line, indented by the recursion level.
The default value is nil.
Also see edebug-tracing, in section Trace Buffer.
nil, Edebug tests coverage of all expressions debugged.
See section Coverage Testing.
nil, continue defining or executing any keyboard macro
that is executing outside of Edebug. Use this with caution since it is not
debugged.
See section Edebug Execution Modes.
debug-on-error to this value, if
debug-on-error was previously nil. See section Trapping Errors.
debug-on-quit to this value, if
debug-on-quit was previously nil. See section Trapping Errors.
If you change the values of edebug-on-error or
edebug-on-quit while Edebug is active, their values won't be used
until the next time Edebug is invoked via a new command.
nil, an expression to test for at every stop point.
If the result is non-nil, then break. Errors are ignored.
See section Global Break Condition.
The Lisp reader reports invalid syntax, but cannot say where the real problem is. For example, the error "End of file during parsing" in evaluating an expression indicates an excess of open parentheses (or square brackets). The reader detects this imbalance at the end of the file, but it cannot figure out where the close parenthesis should have been. Likewise, "Invalid read syntax: ")"" indicates an excess close parenthesis or missing open parenthesis, but does not say where the missing parenthesis belongs. How, then, to find what to change?
If the problem is not simply an imbalance of parentheses, a useful technique is to try C-M-e at the beginning of each defun, and see if it goes to the place where that defun appears to end. If it does not, there is a problem in that defun.
However, unmatched parentheses are the most common syntax errors in Lisp, and we can give further advice for those cases. (In addition, just moving point through the code with Show Paren mode enabled might find the mismatch.)
The first step is to find the defun that is unbalanced. If there is
an excess open parenthesis, the way to do this is to insert a
close parenthesis at the end of the file and type C-M-b
(backward-sexp). This will move you to the beginning of the
defun that is unbalanced. (Then type C-SPC C-_ C-u
C-SPC to set the mark there, undo the insertion of the
close parenthesis, and finally return to the mark.)
The next step is to determine precisely what is wrong. There is no way to be sure of this except by studying the program, but often the existing indentation is a clue to where the parentheses should have been. The easiest way to use this clue is to reindent with C-M-q and see what moves. But don't do this yet! Keep reading, first.
Before you do this, make sure the defun has enough close parentheses. Otherwise, C-M-q will get an error, or will reindent all the rest of the file until the end. So move to the end of the defun and insert a close parenthesis there. Don't use C-M-e to move there, since that too will fail to work until the defun is balanced.
Now you can go to the beginning of the defun and type C-M-q. Usually all the lines from a certain point to the end of the function will shift to the right. There is probably a missing close parenthesis, or a superfluous open parenthesis, near that point. (However, don't assume this is true; study the code to make sure.) Once you have found the discrepancy, undo the C-M-q with C-_, since the old indentation is probably appropriate to the intended parentheses.
After you think you have fixed the problem, use C-M-q again. If the old indentation actually fit the intended nesting of parentheses, and you have put back those parentheses, C-M-q should not change anything.
To deal with an excess close parenthesis, first insert an open parenthesis at the beginning of the file, back up over it, and type C-M-f to find the end of the unbalanced defun. (Then type C-SPC C-_ C-u C-SPC to set the mark there, undo the insertion of the open parenthesis, and finally return to the mark.)
Then find the actual matching close parenthesis by typing C-M-f at the beginning of that defun. This will leave you somewhere short of the place where the defun ought to end. It is possible that you will find a spurious close parenthesis in that vicinity.
If you don't see a problem at that point, the next thing to do is to type C-M-q at the beginning of the defun. A range of lines will probably shift left; if so, the missing open parenthesis or spurious close parenthesis is probably near the first of those lines. (However, don't assume this is true; study the code to make sure.) Once you have found the discrepancy, undo the C-M-q with C-_, since the old indentation is probably appropriate to the intended parentheses.
After you think you have fixed the problem, use C-M-q again. If the old indentation actually fit the intended nesting of parentheses, and you have put back those parentheses, C-M-q should not change anything.
When an error happens during byte compilation, it is normally due to invalid syntax in the program you are compiling. The compiler prints a suitable error message in the `*Compile-Log*' buffer, and then stops. The message may state a function name in which the error was found, or it may not. Either way, here is how to find out where in the file the error occurred.
What you should do is switch to the buffer ` *Compiler Input*'. (Note that the buffer name starts with a space, so it does not show up in M-x list-buffers.) This buffer contains the program being compiled, and point shows how far the byte compiler was able to read.
If the error was due to invalid Lisp syntax, point shows exactly where the invalid syntax was detected. The cause of the error is not necessarily near by! Use the techniques in the previous section to find the error.
If the error was detected while compiling a form that had been read successfully, then point is located at the end of the form. In this case, this technique can't localize the error precisely, but can still show you which function to check.
Printing and reading are the operations of converting Lisp objects to textual form and vice versa. They use the printed representations and read syntax described in section Lisp Data Types.
This chapter describes the Lisp functions for reading and printing. It also describes streams, which specify where to get the text (if reading) or where to put it (if printing).
Reading a Lisp object means parsing a Lisp expression in textual
form and producing a corresponding Lisp object. This is how Lisp
programs get into Lisp from files of Lisp code. We call the text the
read syntax of the object. For example, the text `(a . 5)'
is the read syntax for a cons cell whose CAR is a and whose
CDR is the number 5.
Printing a Lisp object means producing text that represents that object--converting the object to its printed representation (see section Printed Representation and Read Syntax). Printing the cons cell described above produces the text `(a . 5)'.
Reading and printing are more or less inverse operations: printing the
object that results from reading a given piece of text often produces
the same text, and reading the text that results from printing an object
usually produces a similar-looking object. For example, printing the
symbol foo produces the text `foo', and reading that text
returns the symbol foo. Printing a list whose elements are
a and b produces the text `(a b)', and reading that
text produces a list (but not the same list) with elements a
and b.
However, these two operations are not precisely inverses. There are three kinds of exceptions:
Most of the Lisp functions for reading text take an input stream as an argument. The input stream specifies where or how to get the characters of the text to be read. Here are the possible types of input stream:
t
t used as a stream means that the input is read from the
minibuffer. In fact, the minibuffer is invoked once and the text
given by the user is made into a string that is then used as the
input stream.
nil
nil supplied as an input stream means to use the value of
standard-input instead; that value is the default input
stream, and must be a non-nil input stream.
Here is an example of reading from a stream that is a buffer, showing where point is located before and after:
---------- Buffer: foo ----------
This-!- is the contents of foo.
---------- Buffer: foo ----------
(read (get-buffer "foo"))
=> is
(read (get-buffer "foo"))
=> the
---------- Buffer: foo ----------
This is the-!- contents of foo.
---------- Buffer: foo ----------
Note that the first read skips a space. Reading skips any amount of whitespace preceding the significant text.
Here is an example of reading from a stream that is a marker,
initially positioned at the beginning of the buffer shown. The value
read is the symbol This.
---------- Buffer: foo ----------
This is the contents of foo.
---------- Buffer: foo ----------
(setq m (set-marker (make-marker) 1 (get-buffer "foo")))
=> #<marker at 1 in foo>
(read m)
=> This
m
=> #<marker at 5 in foo> ;; Before the first space.
Here we read from the contents of a string:
(read "(When in) the course")
=> (When in)
The following example reads from the minibuffer. The
prompt is: `Lisp expression: '. (That is always the prompt
used when you read from the stream t.) The user's input is shown
following the prompt.
(read t)
=> 23
---------- Buffer: Minibuffer ----------
Lisp expression: 23 RET
---------- Buffer: Minibuffer ----------
Finally, here is an example of a stream that is a function, named
useless-stream. Before we use the stream, we initialize the
variable useless-list to a list of characters. Then each call to
the function useless-stream obtains the next character in the list
or unreads a character by adding it to the front of the list.
(setq useless-list (append "XY()" nil))
=> (88 89 40 41)
(defun useless-stream (&optional unread)
(if unread
(setq useless-list (cons unread useless-list))
(prog1 (car useless-list)
(setq useless-list (cdr useless-list)))))
=> useless-stream
Now we read using the stream thus constructed:
(read 'useless-stream)
=> XY
useless-list
=> (40 41)
Note that the open and close parentheses remain in the list. The Lisp
reader encountered the open parenthesis, decided that it ended the
input, and unread it. Another attempt to read from the stream at this
point would read `()' and return nil.
load. Don't use this function
yourself.
This section describes the Lisp functions and variables that pertain to reading.
In the functions below, stream stands for an input stream (see
the previous section). If stream is nil or omitted, it
defaults to the value of standard-input.
An end-of-file error is signaled if reading encounters an
unterminated list, vector, or string.
If start is supplied, then reading begins at index start in the string (where the first character is at index 0). If you specify end, then reading is forced to stop just before that index, as if the rest of the string were not there.
For example:
(read-from-string "(setq x 55) (setq y 5)")
=> ((setq x 55) . 11)
(read-from-string "\"A short string\"")
=> ("A short string" . 16)
;; Read starting at the first character.
(read-from-string "(list 112)" 0)
=> ((list 112) . 10)
;; Read starting at the second character.
(read-from-string "(list 112)" 1)
=> (list . 5)
;; Read starting at the seventh character,
;; and stopping at the ninth.
(read-from-string "(list 112)" 6 8)
=> (11 . 8)
read uses when the stream argument is nil.
An output stream specifies what to do with the characters produced by printing. Most print functions accept an output stream as an optional argument. Here are the possible types of output stream:
t
nil
nil specified as an output stream means to use the value of
standard-output instead; that value is the default output
stream, and must not be nil.
Many of the valid output streams are also valid as input streams. The difference between input and output streams is therefore more a matter of how you use a Lisp object, than of different types of object.
Here is an example of a buffer used as an output stream. Point is initially located as shown immediately before the `h' in `the'. At the end, point is located directly before that same `h'.
---------- Buffer: foo ----------
This is t-!-he contents of foo.
---------- Buffer: foo ----------
(print "This is the output" (get-buffer "foo"))
=> "This is the output"
---------- Buffer: foo ----------
This is t
"This is the output"
-!-he contents of foo.
---------- Buffer: foo ----------
Now we show a use of a marker as an output stream. Initially, the
marker is in buffer foo, between the `t' and the `h' in
the word `the'. At the end, the marker has advanced over the
inserted text so that it remains positioned before the same `h'.
Note that the location of point, shown in the usual fashion, has no
effect.
---------- Buffer: foo ----------
This is the -!-output
---------- Buffer: foo ----------
(setq m (copy-marker 10))
=> #<marker at 10 in foo>
(print "More output for foo." m)
=> "More output for foo."
---------- Buffer: foo ----------
This is t
"More output for foo."
he -!-output
---------- Buffer: foo ----------
m
=> #<marker at 34 in foo>
The following example shows output to the echo area:
(print "Echo Area output" t)
=> "Echo Area output"
---------- Echo Area ----------
"Echo Area output"
---------- Echo Area ----------
Finally, we show the use of a function as an output stream. The
function eat-output takes each character that it is given and
conses it onto the front of the list last-output (see section Building Cons Cells and Lists). At the end, the list contains all the characters output, but
in reverse order.
(setq last-output nil)
=> nil
(defun eat-output (c)
(setq last-output (cons c last-output)))
=> eat-output
(print "This is the output" 'eat-output)
=> "This is the output"
last-output
=> (10 34 116 117 112 116 117 111 32 101 104
116 32 115 105 32 115 105 104 84 34 10)
Now we can put the output in the proper order by reversing the list:
(concat (nreverse last-output))
=> "
\"This is the output\"
"
Calling concat converts the list to a string so you can see its
contents more clearly.
This section describes the Lisp functions for printing Lisp objects--converting objects into their printed representation.
Some of the Emacs printing functions add quoting characters to the output when necessary so that it can be read properly. The quoting characters used are `"' and `\'; they distinguish strings from symbols, and prevent punctuation characters in strings and symbols from being taken as delimiters when reading. See section Printed Representation and Read Syntax, for full details. You specify quoting or no quoting by the choice of printing function.
If the text is to be read back into Lisp, then you should print with quoting characters to avoid ambiguity. Likewise, if the purpose is to describe a Lisp object clearly for a Lisp programmer. However, if the purpose of the output is to look nice for humans, then it is usually better to print without quoting.
Lisp objects can refer to themselves. Printing a self-referential object in the normal way would require an infinite amount of text, and the attempt could cause infinite recursion. Emacs detects such recursion and prints `#level' instead of recursively printing an object already being printed. For example, here `#0' indicates a recursive reference to the object at level 0 of the current print operation:
(setq foo (list nil))
=> (nil)
(setcar foo foo)
=> (#0)
In the functions below, stream stands for an output stream.
(See the previous section for a description of output streams.) If
stream is nil or omitted, it defaults to the value of
standard-output.
print function is a convenient way of printing. It outputs
the printed representation of object to stream, printing in
addition one newline before object and another after it. Quoting
characters are used. print returns object. For example:
(progn (print 'The\ cat\ in)
(print "the hat")
(print " came back"))
-|
-| The\ cat\ in
-|
-| "the hat"
-|
-| " came back"
-|
=> " came back"
print does, but it does use quoting characters just like
print. It returns object.
(progn (prin1 'The\ cat\ in)
(prin1 "the hat")
(prin1 " came back"))
-| The\ cat\ in"the hat"" came back"
=> " came back"
This function is intended to produce output that is readable by people,
not by read, so it doesn't insert quoting characters and doesn't
put double-quotes around the contents of strings. It does not add any
spacing between calls.
(progn
(princ 'The\ cat)
(princ " in the \"hat\""))
-| The cat in the "hat"
=> " in the \"hat\""
prin1
would have printed for the same argument.
(prin1-to-string 'foo)
=> "foo"
(prin1-to-string (mark-marker))
=> "#<marker at 2773 in strings.texi>"
If noescape is non-nil, that inhibits use of quoting
characters in the output. (This argument is supported in Emacs versions
19 and later.)
(prin1-to-string "foo")
=> "\"foo\""
(prin1-to-string "foo" t)
=> "foo"
See format, in section Conversion of Characters and Strings, for other ways to obtain
the printed representation of a Lisp object as a string.
standard-output set
up to feed output into a string. Then it returns that string.
For example, if the current buffer name is `foo',
(with-output-to-string (princ "The buffer is ") (princ (buffer-name)))
returns "The buffer is foo".
nil.
nil, then newline characters in strings
are printed as `\n' and formfeeds are printed as `\f'.
Normally these characters are printed as actual newlines and formfeeds.
This variable affects the print functions prin1 and print
that print with quoting. It does not affect princ. Here is an
example using prin1:
(prin1 "a\nb")
-| "a
-| b"
=> "a
b"
(let ((print-escape-newlines t))
(prin1 "a\nb"))
-| "a\nb"
=> "a
b"
In the second expression, the local binding of
print-escape-newlines is in effect during the call to
prin1, but not during the printing of the result.
nil, then unibyte non-ASCII
characters in strings are unconditionally printed as backslash sequences
by the print functions prin1 and print that print with
quoting.
Those functions also use backslash sequences for unibyte non-ASCII characters, regardless of the value of this variable, when the output stream is a multibyte buffer or a marker pointing into one.
nil, then multibyte non-ASCII
characters in strings are unconditionally printed as backslash sequences
by the print functions prin1 and print that print with
quoting.
Those functions also use backslash sequences for multibyte non-ASCII characters, regardless of the value of this variable, when the output stream is a unibyte buffer or a marker pointing into one.
If the value is nil (the default), then there is no limit.
(setq print-length 2)
=> 2
(print '(1 2 3 4 5))
-| (1 2 ...)
=> (1 2 ...)
nil (which is the default) means no limit.
A minibuffer is a special buffer that Emacs commands use to read arguments more complicated than the single numeric prefix argument. These arguments include file names, buffer names, and command names (as in M-x). The minibuffer is displayed on the bottom line of the frame, in the same place as the echo area, but only while it is in use for reading an argument.
In most ways, a minibuffer is a normal Emacs buffer. Most operations within a buffer, such as editing commands, work normally in a minibuffer. However, many operations for managing buffers do not apply to minibuffers. The name of a minibuffer always has the form ` *Minibuf-number', and it cannot be changed. Minibuffers are displayed only in special windows used only for minibuffers; these windows always appear at the bottom of a frame. (Sometimes frames have no minibuffer window, and sometimes a special kind of frame contains nothing but a minibuffer window; see section Minibuffers and Frames.)
The minibuffer's window is normally a single line. You can resize it temporarily with the window sizing commands; it reverts to its normal size when the minibuffer is exited. You can resize it permanently by using the window sizing commands in the frame's other window, when the minibuffer is not active. If the frame contains just a minibuffer, you can change the minibuffer's size by changing the frame's size.
If a command uses a minibuffer while there is an active minibuffer,
this is called a recursive minibuffer. The first minibuffer is
named ` *Minibuf-0*'. Recursive minibuffers are named by
incrementing the number at the end of the name. (The names begin with a
space so that they won't show up in normal buffer lists.) Of several
recursive minibuffers, the innermost (or most recently entered) is the
active minibuffer. We usually call this "the" minibuffer. You can
permit or forbid recursive minibuffers by setting the variable
enable-recursive-minibuffers or by putting properties of that
name on command symbols (see section Minibuffer Miscellany).
Like other buffers, a minibuffer may use any of several local keymaps (see section Keymaps); these contain various exit commands and in some cases completion commands (see section Completion).
minibuffer-local-map is for ordinary input (no completion).
minibuffer-local-ns-map is similar, except that SPC exits
just like RET. This is used mainly for Mocklisp compatibility.
minibuffer-local-completion-map is for permissive completion.
minibuffer-local-must-match-map is for strict completion and
for cautious completion.
Most often, the minibuffer is used to read text as a string. It can
also be used to read a Lisp object in textual form. The most basic
primitive for minibuffer input is read-from-minibuffer; it can do
either one.
In most cases, you should not call minibuffer input functions in the
middle of a Lisp function. Instead, do all minibuffer input as part of
reading the arguments for a command, in the interactive
specification. See section Defining Commands.
nil, then it uses
read to convert the text into a Lisp object (see section Input Functions).
The first thing this function does is to activate a minibuffer and display it with prompt-string as the prompt. This value must be a string. Then the user can edit text in the minibuffer.
When the user types a command to exit the minibuffer,
read-from-minibuffer constructs the return value from the text in
the minibuffer. Normally it returns a string containing that text.
However, if read is non-nil, read-from-minibuffer
reads the text and returns the resulting Lisp object, unevaluated.
(See section Input Functions, for information about reading.)
The argument default specifies a default value to make available
through the history commands. It should be a string, or nil. If
read is non-nil, then default is also used as the
input to read, if the user enters empty input. However, in the
usual case (where read is nil), read-from-minibuffer
does not return default when the user enters empty input; it
returns an empty string, "". In this respect, it is different
from all the other minibuffer input functions in this chapter.
If keymap is non-nil, that keymap is the local keymap to
use in the minibuffer. If keymap is omitted or nil, the
value of minibuffer-local-map is used as the keymap. Specifying
a keymap is the most important way to customize the minibuffer for
various applications such as completion.
The argument hist specifies which history list variable to use
for saving the input and for history commands used in the minibuffer.
It defaults to minibuffer-history. See section Minibuffer History.
If the variable minibuffer-allow-text-properties is
non-nil, then the string which is returned includes whatever text
properties were present in the minibuffer. Otherwise all the text
properties are stripped when the value is returned.
If the argument inherit-input-method is non-nil, then the
minibuffer inherits the current input method (see section Input Methods) and
the setting of enable-multibyte-characters (see section Text Representations) from whichever buffer was current before entering the
minibuffer.
If initial-contents is a string, read-from-minibuffer
inserts it into the minibuffer, leaving point at the end, before the
user starts to edit the text. The minibuffer appears with this text as
its initial contents.
Alternatively, initial-contents can be a cons cell of the form
(string . position). This means to insert
string in the minibuffer but put point position characters
from the beginning, rather than at the end.
Usage note: The initial-contents argument and the
default argument are two alternative features for more or less the
same job. It does not make sense to use both features in a single call
to read-from-minibuffer. In general, we recommend using
default, since this permits the user to insert the default value
when it is wanted, but does not burden the user with deleting it from
the minibuffer on other occasions.
read-from-minibuffer. The keymap used is
minibuffer-local-map.
The optional argument history, if non-nil, specifies a history list and optionally the initial position in the list. The optional argument default specifies a default value to return if the user enters null input; it should be a string. The optional argument inherit-input-method specifies whether to inherit the current buffer's input method.
This function is a simplified interface to the
read-from-minibuffer function:
(read-string prompt initial history default inherit)
==
(let ((value
(read-from-minibuffer prompt initial nil nil
history default inherit)))
(if (equal value "")
default
value))
nil, then read-from-minibuffer strips
all text properties from the minibuffer input before returning it.
Since all minibuffer input uses read-from-minibuffer, this
variable applies to all minibuffer input.
Note that the completion functions discard text properties unconditionally, regardless of the value of this variable.
exit-minibuffer
exit-minibuffer
abort-recursive-edit
next-history-element
previous-history-element
next-matching-history-element
previous-matching-history-element
read-from-minibuffer.
This is a simplified interface to the read-from-minibuffer
function, and passes the value of the minibuffer-local-ns-map
keymap as the keymap argument for that function. Since the keymap
minibuffer-local-ns-map does not rebind C-q, it is
possible to put a space into the string, by quoting it.
(read-no-blanks-input prompt initial) == (read-from-minibuffer prompt initial minibuffer-local-ns-map)
read-no-blanks-input. By default, it makes the
following bindings, in addition to those of minibuffer-local-map:
exit-minibuffer
exit-minibuffer
self-insert-and-exit
This section describes functions for reading Lisp objects with the minibuffer.
read-from-minibuffer.
This is a simplified interface to the
read-from-minibuffer function:
(read-minibuffer prompt initial) == (read-from-minibuffer prompt initial nil t)
Here is an example in which we supply the string "(testing)" as
initial input:
(read-minibuffer "Enter an expression: " (format "%s" '(testing))) ;; Here is how the minibuffer is displayed: ---------- Buffer: Minibuffer ---------- Enter an expression: (testing)-!- ---------- Buffer: Minibuffer ----------
The user can type RET immediately to use the initial input as a default, or can edit the input.
read-from-minibuffer.
This function simply evaluates the result of a call to
read-minibuffer:
(eval-minibuffer prompt initial) == (eval (read-minibuffer prompt initial))
eval-minibuffer is that here the initial form is not
optional and it is treated as a Lisp object to be converted to printed
representation rather than as a string of text. It is printed with
prin1, so if it is a string, double-quote characters (`"')
appear in the initial text. See section Output Functions.
The first thing edit-and-eval-command does is to activate the
minibuffer with prompt as the prompt. Then it inserts the printed
representation of form in the minibuffer, and lets the user edit it.
When the user exits the minibuffer, the edited text is read with
read and then evaluated. The resulting value becomes the value
of edit-and-eval-command.
In the following example, we offer the user an expression with initial text which is a valid form already:
(edit-and-eval-command "Please edit: " '(forward-word 1)) ;; After evaluation of the preceding expression, ;; the following appears in the minibuffer: ---------- Buffer: Minibuffer ---------- Please edit: (forward-word 1)-!- ---------- Buffer: Minibuffer ----------
Typing RET right away would exit the minibuffer and evaluate the
expression, thus moving point forward one word.
edit-and-eval-command returns nil in this example.
A minibuffer history list records previous minibuffer inputs so the user can reuse them conveniently. A history list is actually a symbol, not a list; it is a variable whose value is a list of strings (previous inputs), most recent first.
There are many separate history lists, used for different kinds of inputs. It's the Lisp programmer's job to specify the right history list for each use of the minibuffer.
The basic minibuffer input functions read-from-minibuffer and
completing-read both accept an optional argument named hist
which is how you specify the history list. Here are the possible
values:
If you don't specify hist, then the default history list
minibuffer-history is used. For other standard history lists,
see below. You can also create your own history list variable; just
initialize it to nil before the first use.
Both read-from-minibuffer and completing-read add new
elements to the history list automatically, and provide commands to
allow the user to reuse items on the list. The only thing your program
needs to do to use a history list is to initialize it and to pass its
name to the input functions when you wish. But it is safe to modify the
list by hand when the minibuffer input functions are not using it.
Here are some of the standard minibuffer history list variables:
query-replace (and similar
arguments to other commands).
Completion is a feature that fills in the rest of a name
starting from an abbreviation for it. Completion works by comparing the
user's input against a list of valid names and determining how much of
the name is determined uniquely by what the user has typed. For
example, when you type C-x b (switch-to-buffer) and then
type the first few letters of the name of the buffer to which you wish
to switch, and then type TAB (minibuffer-complete), Emacs
extends the name as far as it can.
Standard Emacs commands offer completion for names of symbols, files, buffers, and processes; with the functions in this section, you can implement completion for other kinds of names.
The try-completion function is the basic primitive for
completion: it returns the longest determined completion of a given
initial string, with a given set of strings to match against.
The function completing-read provides a higher-level interface
for completion. A call to completing-read specifies how to
determine the list of valid names. The function then activates the
minibuffer with a local keymap that binds a few keys to commands useful
for completion. Other functions provide convenient simple interfaces
for reading certain kinds of names with completion.
The two functions try-completion and all-completions
have nothing in themselves to do with minibuffers. We describe them in
this chapter so as to keep them near the higher-level completion
features that do use the minibuffer.
Completion compares string against each of the permissible
completions specified by collection; if the beginning of the
permissible completion equals string, it matches. If no permissible
completions match, try-completion returns nil. If only
one permissible completion matches, and the match is exact, then
try-completion returns t. Otherwise, the value is the
longest initial sequence common to all the permissible completions that
match.
If collection is an alist (see section Association Lists), the CARs of the alist elements form the set of permissible completions.
If collection is an obarray (see section Creating and Interning Symbols), the names
of all symbols in the obarray form the set of permissible completions. The
global variable obarray holds an obarray containing the names of
all interned Lisp symbols.
Note that the only valid way to make a new obarray is to create it
empty and then add symbols to it one by one using intern.
Also, you cannot intern a given symbol in more than one obarray.
If the argument predicate is non-nil, then it must be a
function of one argument. It is used to test each possible match, and
the match is accepted only if predicate returns non-nil.
The argument given to predicate is either a cons cell from the alist
(the CAR of which is a string) or else it is a symbol (not a
symbol name) from the obarray.
You can also use a symbol that is a function as collection. Then
the function is solely responsible for performing completion;
try-completion returns whatever this function returns. The
function is called with three arguments: string, predicate
and nil. (The reason for the third argument is so that the same
function can be used in all-completions and do the appropriate
thing in either case.) See section Programmed Completion.
In the first of the following examples, the string `foo' is
matched by three of the alist CARs. All of the matches begin with
the characters `fooba', so that is the result. In the second
example, there is only one possible match, and it is exact, so the value
is t.
(try-completion
"foo"
'(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4)))
=> "fooba"
(try-completion "foo" '(("barfoo" 2) ("foo" 3)))
=> t
In the following example, numerous symbols begin with the characters `forw', and all of them begin with the word `forward'. In most of the symbols, this is followed with a `-', but not in all, so no more than `forward' can be completed.
(try-completion "forw" obarray)
=> "forward"
Finally, in the following example, only two of the three possible
matches pass the predicate test (the string `foobaz' is
too short). Both of those begin with the string `foobar'.
(defun test (s)
(> (length (car s)) 6))
=> test
(try-completion
"foo"
'(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4))
'test)
=> "foobar"
try-completion.
If collection is a function, it is called with three arguments:
string, predicate and t; then all-completions
returns whatever the function returns. See section Programmed Completion.
If nospace is non-nil, completions that start with a space
are ignored unless string also starts with a space.
Here is an example, using the function test shown in the
example for try-completion:
(defun test (s)
(> (length (car s)) 6))
=> test
(all-completions
"foo"
'(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4))
'test)
=> ("foobar1" "foobar2")
nil, Emacs does not consider case significant in completion.
This section describes the basic interface for reading from the minibuffer with completion.
The actual completion is done by passing collection and
predicate to the function try-completion. This happens in
certain commands bound in the local keymaps used for completion.
If require-match is nil, the exit commands work regardless
of the input in the minibuffer. If require-match is t, the
usual minibuffer exit commands won't exit unless the input completes to
an element of collection. If require-match is neither
nil nor t, then the exit commands won't exit unless the
input already in the buffer matches an element of collection.
However, empty input is always permitted, regardless of the value of
require-match; in that case, completing-read returns
default. The value of default (if non-nil) is also
available to the user through the history commands.
The user can exit with null input by typing RET with an empty
minibuffer. Then completing-read returns "". This is how
the user requests whatever default the command uses for the value being
read. The user can return using RET in this way regardless of the
value of require-match, and regardless of whether the empty string
is included in collection.
The function completing-read works by calling
read-minibuffer. It uses minibuffer-local-completion-map
as the keymap if require-match is nil, and uses
minibuffer-local-must-match-map if require-match is
non-nil. See section Minibuffer Commands That Do Completion.
The argument hist specifies which history list variable to use for
saving the input and for minibuffer history commands. It defaults to
minibuffer-history. See section Minibuffer History.
If initial is non-nil, completing-read inserts it
into the minibuffer as part of the input. Then it allows the user to
edit the input, providing several commands to attempt completion.
In most cases, we recommend using default, and not initial.
If the argument inherit-input-method is non-nil, then the
minibuffer inherits the current input method (see section Input Methods) and the setting of enable-multibyte-characters
(see section Text Representations) from whichever buffer was current before
entering the minibuffer.
Completion ignores case when comparing the input against the possible
matches, if the built-in variable completion-ignore-case is
non-nil. See section Basic Completion Functions.
Here's an example of using completing-read:
(completing-read
"Complete a foo: "
'(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4))
nil t "fo")
;; After evaluation of the preceding expression,
;; the following appears in the minibuffer:
---------- Buffer: Minibuffer ----------
Complete a foo: fo-!-
---------- Buffer: Minibuffer ----------
If the user then types DEL DEL b RET,
completing-read returns barfoo.
The completing-read function binds three variables to pass
information to the commands that actually do completion. These
variables are minibuffer-completion-table,
minibuffer-completion-predicate and
minibuffer-completion-confirm. For more information about them,
see section Minibuffer Commands That Do Completion.
This section describes the keymaps, commands and user options used in the minibuffer to do completion.
completing-read uses this value as the local keymap when an
exact match of one of the completions is not required. By default, this
keymap makes the following bindings:
minibuffer-completion-help
minibuffer-complete-word
minibuffer-complete
with other characters bound as in minibuffer-local-map
(see section Reading Text Strings with the Minibuffer).
completing-read uses this value as the local keymap when an
exact match of one of the completions is required. Therefore, no keys
are bound to exit-minibuffer, the command that exits the
minibuffer unconditionally. By default, this keymap makes the following
bindings:
minibuffer-completion-help
minibuffer-complete-word
minibuffer-complete
minibuffer-complete-and-exit
minibuffer-complete-and-exit
with other characters bound as in minibuffer-local-map.
completing-read passes to try-completion. It is used by
minibuffer completion commands such as minibuffer-complete-word.
completing-read
passes to try-completion. The variable is also used by the other
minibuffer completion functions.
minibuffer-complete-word does not add any characters beyond the
first character that is not a word constituent. See section Syntax Tables.
minibuffer-completion-confirm is nil. If confirmation
is required, it is given by repeating this command
immediately--the command is programmed to work without confirmation
when run twice in succession.
nil, Emacs asks for
confirmation of a completion before exiting the minibuffer. The
function minibuffer-complete-and-exit checks the value of this
variable before it exits.
all-completions
using the value of the variable minibuffer-completion-table as
the collection argument, and the value of
minibuffer-completion-predicate as the predicate argument.
The list of completions is displayed as text in a buffer named
`*Completions*'.
standard-output, usually a buffer. (See section Reading and Printing Lisp Objects, for more
information about streams.) The argument completions is normally
a list of completions just returned by all-completions, but it
does not have to be. Each element may be a symbol or a string, either
of which is simply printed, or a list of two strings, which is printed
as if the strings were concatenated.
This function is called by minibuffer-completion-help. The
most common way to use it is together with
with-output-to-temp-buffer, like this:
(with-output-to-temp-buffer "*Completions*"
(display-completion-list
(all-completions (buffer-string) my-alist)))
nil, the completion commands
automatically display a list of possible completions whenever nothing
can be completed because the next character is not uniquely determined.
This section describes the higher-level convenient functions for reading certain sorts of names with completion.
In most cases, you should not call these functions in the middle of a
Lisp function. When possible, do all minibuffer input as part of
reading the arguments for a command, in the interactive
specification. See section Defining Commands.
nil,
it should be a string or a buffer. It is mentioned in the prompt, but
is not inserted in the minibuffer as initial input.
If existing is non-nil, then the name specified must be
that of an existing buffer. The usual commands to exit the minibuffer
do not exit if the text is not valid, and RET does completion to
attempt to find a valid name. (However, default is not checked
for validity; it is returned, whatever it is, if the user exits with the
minibuffer empty.)
In the following example, the user enters `minibuffer.t', and
then types RET. The argument existing is t, and the
only buffer name starting with the given input is
`minibuffer.texi', so that name is the value.
(read-buffer "Buffer name? " "foo" t)
;; After evaluation of the preceding expression,
;; the following prompt appears,
;; with an empty minibuffer:
---------- Buffer: Minibuffer ----------
Buffer name? (default foo) -!-
---------- Buffer: Minibuffer ----------
;; The user types minibuffer.t RET.
=> "minibuffer.texi"
iswitchb-read-buffer, all Emacs commands
that call read-buffer to read a buffer name will actually use the
iswitchb package to read it.
read-from-minibuffer. Recall that a command is anything for
which commandp returns t, and a command name is a symbol
for which commandp returns t. See section Interactive Call.
The argument default specifies what to return if the user enters
null input. It can be a symbol or a string; if it is a string,
read-command interns it before returning it. If default is
nil, that means no default has been specified; then if the user
enters null input, the return value is nil.
(read-command "Command name? ") ;; After evaluation of the preceding expression, ;; the following prompt appears with an empty minibuffer: ---------- Buffer: Minibuffer ---------- Command name? ---------- Buffer: Minibuffer ----------
If the user types forward-c RET, then this function returns
forward-char.
The read-command function is a simplified interface to
completing-read. It uses the variable obarray so as to
complete in the set of extant Lisp symbols, and it uses the
commandp predicate so as to accept only command names:
(read-command prompt)
==
(intern (completing-read prompt obarray
'commandp t nil))
The argument default specifies what to return if the user enters
null input. It can be a symbol or a string; if it is a string,
read-variable interns it before returning it. If default
is nil, that means no default has been specified; then if the
user enters null input, the return value is nil.
(read-variable "Variable name? ") ;; After evaluation of the preceding expression, ;; the following prompt appears, ;; with an empty minibuffer: ---------- Buffer: Minibuffer ---------- Variable name? -!- ---------- Buffer: Minibuffer ----------
If the user then types fill-p RET, read-variable
returns fill-prefix.
This function is similar to read-command, but uses the
predicate user-variable-p instead of commandp:
(read-variable prompt)
==
(intern
(completing-read prompt obarray
'user-variable-p t nil))
See also the functions read-coding-system and
read-non-nil-coding-system, in section User-Chosen Coding Systems.
Here is another high-level completion function, designed for reading a file name. It provides special features including automatic insertion of the default directory.
nil, then the function returns default if the user just
types RET. default is not checked for validity; it is
returned, whatever it is, if the user exits with the minibuffer empty.
If existing is non-nil, then the user must specify the name
of an existing file; RET performs completion to make the name
valid if possible, and then refuses to exit if it is not valid. If the
value of existing is neither nil nor t, then
RET also requires confirmation after completion. If
existing is nil, then the name of a nonexistent file is
acceptable.
The argument directory specifies the directory to use for
completion of relative file names. If insert-default-directory
is non-nil, directory is also inserted in the minibuffer as
initial input. It defaults to the current buffer's value of
default-directory.
If you specify initial, that is an initial file name to insert in
the buffer (after directory, if that is inserted). In this
case, point goes at the beginning of initial. The default for
initial is nil---don't insert any file name. To see what
initial does, try the command C-x C-v. Note: we
recommend using default rather than initial in most cases.
Here is an example:
(read-file-name "The file is ") ;; After evaluation of the preceding expression, ;; the following appears in the minibuffer: ---------- Buffer: Minibuffer ---------- The file is /gp/gnu/elisp/-!- ---------- Buffer: Minibuffer ----------
Typing manual TAB results in the following:
---------- Buffer: Minibuffer ---------- The file is /gp/gnu/elisp/manual.texi-!- ---------- Buffer: Minibuffer ----------
If the user types RET, read-file-name returns the file name
as the string "/gp/gnu/elisp/manual.texi".
read-file-name. Its value controls
whether read-file-name starts by placing the name of the default
directory in the minibuffer, plus the initial file name if any. If the
value of this variable is nil, then read-file-name does
not place any initial input in the minibuffer (unless you specify
initial input with the initial argument). In that case, the
default directory is still used for completion of relative file names,
but is not displayed.
For example:
;; Here the minibuffer starts out with the default directory. (let ((insert-default-directory t)) (read-file-name "The file is ")) ---------- Buffer: Minibuffer ---------- The file is ~lewis/manual/-!- ---------- Buffer: Minibuffer ---------- ;; Here the minibuffer is empty and only the prompt ;; appears on its line. (let ((insert-default-directory nil)) (read-file-name "The file is ")) ---------- Buffer: Minibuffer ---------- The file is -!- ---------- Buffer: Minibuffer ----------
Sometimes it is not possible to create an alist or an obarray containing all the intended possible completions. In such a case, you can supply your own function to compute the completion of a given string. This is called programmed completion.
To use this feature, pass a symbol with a function definition as the
collection argument to completing-read. The function
completing-read arranges to pass your completion function along
to try-completion and all-completions, which will then let
your function do all the work.
The completion function should accept three arguments:
nil if
none. Your function should call the predicate for each possible match,
and ignore the possible match if the predicate returns nil.
There are three flag values for three operations:
nil specifies try-completion. The completion function
should return the completion of the specified string, or t if the
string is a unique and exact match already, or nil if the string
matches no possibility.
If the string is an exact match for one possibility, but also matches
other longer possibilities, the function should return the string, not
t.
t specifies all-completions. The completion function
should return a list of all possible completions of the specified
string.
lambda specifies a test for an exact match. The completion
function should return t if the specified string is an exact
match for some possibility; nil otherwise.
It would be consistent and clean for completion functions to allow lambda expressions (lists that are functions) as well as function symbols as collection, but this is impossible. Lists as completion tables are already assigned another meaning--as alists. It would be unreliable to fail to handle an alist normally because it is also a possible function. So you must arrange for any function you wish to use for completion to be encapsulated in a symbol.
Emacs uses programmed completion when completing file names. See section File Name Completion.
This section describes functions used to ask the user a yes-or-no
question. The function y-or-n-p can be answered with a single
character; it is useful for questions where an inadvertent wrong answer
will not have serious consequences. yes-or-no-p is suitable for
more momentous questions, since it requires three or four characters to
answer.
If either of these functions is called in a command that was invoked
using the mouse--more precisely, if last-nonmenu-event
(see section Information from the Command Loop) is either nil or a list--then it
uses a dialog box or pop-up menu to ask the question. Otherwise, it
uses keyboard input. You can force use of the mouse or use of keyboard
input by binding last-nonmenu-event to a suitable value around
the call.
Strictly speaking, yes-or-no-p uses the minibuffer and
y-or-n-p does not; but it seems best to describe them together.
t if the user types y, nil if the
user types n. This function also accepts SPC to mean yes
and DEL to mean no. It accepts C-] to mean "quit", like
C-g, because the question might look like a minibuffer and for
that reason the user might try to use C-] to get out. The answer
is a single character, with no RET needed to terminate it. Upper
and lower case are equivalent.
"Asking the question" means printing prompt in the echo area, followed by the string `(y or n) '. If the input is not one of the expected answers (y, n, SPC, DEL, or something that quits), the function responds `Please answer y or n.', and repeats the request.
This function does not actually use the minibuffer, since it does not allow editing of the answer. It actually uses the echo area (see section The Echo Area), which uses the same screen space as the minibuffer. The cursor moves to the echo area while the question is being asked.
The answers and their meanings, even `y' and `n', are not
hardwired. The keymap query-replace-map specifies them.
See section Search and Replace.
In the following example, the user first types q, which is invalid. At the next prompt the user types y.
(y-or-n-p "Do you need a lift? ") ;; After evaluation of the preceding expression, ;; the following prompt appears in the echo area: ---------- Echo area ---------- Do you need a lift? (y or n) ---------- Echo area ---------- ;; If the user then types q, the following appears: ---------- Echo area ---------- Please answer y or n. Do you need a lift? (y or n) ---------- Echo area ---------- ;; When the user types a valid answer, ;; it is displayed after the question: ---------- Echo area ---------- Do you need a lift? (y or n) y ---------- Echo area ----------
We show successive lines of echo area messages, but only one actually appears on the screen at a time.
y-or-n-p, except that if the user fails to answer within
seconds seconds, this function stops waiting and returns
default-value. It works by setting up a timer; see section Timers for Delayed Execution.
The argument seconds may be an integer or a floating point number.
t if the user enters `yes',
nil if the user types `no'. The user must type RET to
finalize the response. Upper and lower case are equivalent.
yes-or-no-p starts by displaying prompt in the echo area,
followed by `(yes or no) '. The user must type one of the
expected responses; otherwise, the function responds `Please answer
yes or no.', waits about two seconds and repeats the request.
yes-or-no-p requires more work from the user than
y-or-n-p and is appropriate for more crucial decisions.
Here is an example:
(yes-or-no-p "Do you really want to remove everything? ") ;; After evaluation of the preceding expression, ;; the following prompt appears, ;; with an empty minibuffer: ---------- Buffer: minibuffer ---------- Do you really want to remove everything? (yes or no) ---------- Buffer: minibuffer ----------
If the user first types y RET, which is invalid because this function demands the entire word `yes', it responds by displaying these prompts, with a brief pause between them:
---------- Buffer: minibuffer ---------- Please answer yes or no. Do you really want to remove everything? (yes or no) ---------- Buffer: minibuffer ----------
When you have a series of similar questions to ask, such as "Do you
want to save this buffer" for each buffer in turn, you should use
map-y-or-n-p to ask the collection of questions, rather than
asking each question individually. This gives the user certain
convenient facilities such as the ability to answer the whole series at
once.
The value of list specifies the objects to ask questions about.
It should be either a list of objects or a generator function. If it is
a function, it should expect no arguments, and should return either the
next object to ask about, or nil meaning stop asking questions.
The argument prompter specifies how to ask each question. If prompter is a string, the question text is computed like this:
(format prompter object)
where object is the next object to ask about (as obtained from list).
If not a string, prompter should be a function of one argument
(the next object to ask about) and should return the question text. If
the value is a string, that is the question to ask the user. The
function can also return t meaning do act on this object (and
don't ask the user), or nil meaning ignore this object (and don't
ask the user).
The argument actor says how to act on the answers that the user gives. It should be a function of one argument, and it is called with each object that the user says yes for. Its argument is always an object obtained from list.
If the argument help is given, it should be a list of this form:
(singular plural action)
where singular is a string containing a singular noun that describes the objects conceptually being acted on, plural is the corresponding plural noun, and action is a transitive verb describing what actor does.
If you don't specify help, the default is ("object"
"objects" "act on").
Each time a question is asked, the user may enter y, Y, or
SPC to act on that object; n, N, or DEL to skip
that object; ! to act on all following objects; ESC or
q to exit (skip all following objects); . (period) to act on
the current object and then exit; or C-h to get help. These are
the same answers that query-replace accepts. The keymap
query-replace-map defines their meaning for map-y-or-n-p
as well as for query-replace; see section Search and Replace.
You can use action-alist to specify additional possible answers
and what they mean. It is an alist of elements of the form
(char function help), each of which defines one
additional answer. In this element, char is a character (the
answer); function is a function of one argument (an object from
list); help is a string.
When the user responds with char, map-y-or-n-p calls
function. If it returns non-nil, the object is considered
"acted upon", and map-y-or-n-p advances to the next object in
list. If it returns nil, the prompt is repeated for the
same object.
If map-y-or-n-p is called in a command that was invoked using the
mouse--more precisely, if last-nonmenu-event (see section Information from the Command Loop) is either nil or a list--then it uses a dialog box
or pop-up menu to ask the question. In this case, it does not use
keyboard input or the echo area. You can force use of the mouse or use
of keyboard input by binding last-nonmenu-event to a suitable
value around the call.
The return value of map-y-or-n-p is the number of objects acted on.
To read a password to pass to another program, you can use the
function read-passwd.
The optional argument confirm, if non-nil, says to read the
password twice and insist it must be the same both times. If it isn't
the same, the user has to type it over and over until the last two
times match.
The optional argument default specifies the default password to
return if the user enters empty input. If default is nil,
then read-passwd returns the null string in that case.
This section describes some basic functions and variables related to minibuffers.
last-command-char;
see section Information from the Command Loop).
nil.
help-form
locally inside the minibuffer (see section Help Functions).
nil if none is currently active.
nil, that stands for the current frame. Note
that the minibuffer window used by a frame need not be part of that
frame--a frame that has no minibuffer of its own necessarily uses some
other frame's minibuffer window.
nil if window is a minibuffer window.
It is not correct to determine whether a given window is a minibuffer by
comparing it with the result of (minibuffer-window), because
there can be more than one minibuffer window if there is more than one
frame.
nil if window, assumed to be
a minibuffer window, is currently active.
nil, it should be a window
object. When the function scroll-other-window is called in the
minibuffer, it scrolls this window.
Finally, some functions and variables deal with recursive minibuffers (see section Recursive Editing):
nil, you can invoke commands (such as
find-file) that use minibuffers even while the minibuffer window
is active. Such invocation produces a recursive editing level for a new
minibuffer. The outer-level minibuffer is invisible while you are
editing the inner one.
If this variable is nil, you cannot invoke minibuffer
commands when the minibuffer window is active, not even if you switch to
another window to do it.
If a command name has a property enable-recursive-minibuffers
that is non-nil, then the command can use the minibuffer to read
arguments even if it is invoked from the minibuffer. The minibuffer
command next-matching-history-element (normally M-s in the
minibuffer) uses this feature.
When you run Emacs, it enters the editor command loop almost immediately. This loop reads key sequences, executes their definitions, and displays the results. In this chapter, we describe how these things are done, and the subroutines that allow Lisp programs to do them.
The first thing the command loop must do is read a key sequence, which
is a sequence of events that translates into a command. It does this by
calling the function read-key-sequence. Your Lisp code can also
call this function (see section Key Sequence Input). Lisp programs can also
do input at a lower level with read-event (see section Reading One Event) or discard pending input with discard-input
(see section Miscellaneous Event Input Features).
The key sequence is translated into a command through the currently
active keymaps. See section Key Lookup, for information on how this is done.
The result should be a keyboard macro or an interactively callable
function. If the key is M-x, then it reads the name of another
command, which it then calls. This is done by the command
execute-extended-command (see section Interactive Call).
To execute a command requires first reading the arguments for it.
This is done by calling command-execute (see section Interactive Call). For commands written in Lisp, the interactive
specification says how to read the arguments. This may use the prefix
argument (see section Prefix Command Arguments) or may read with prompting
in the minibuffer (see section Minibuffers). For example, the command
find-file has an interactive specification which says to
read a file name using the minibuffer. The command's function body does
not use the minibuffer; if you call this command from Lisp code as a
function, you must supply the file name string as an ordinary Lisp
function argument.
If the command is a string or vector (i.e., a keyboard macro) then
execute-kbd-macro is used to execute it. You can call this
function yourself (see section Keyboard Macros).
To terminate the execution of a running command, type C-g. This character causes quitting (see section Quitting).
this-command contains the command that is about to
run, and last-command describes the previous command.
See section Hooks.
this-command describes the command that just ran, and
last-command describes the command before that. See section Hooks.
Quitting is suppressed while running pre-command-hook and
post-command-hook. If an error happens while executing one of
these hooks, it terminates execution of the hook, and clears the hook
variable to nil so as to prevent an infinite loop of errors.
A Lisp function becomes a command when its body contains, at top
level, a form that calls the special form interactive. This
form does nothing when actually executed, but its presence serves as a
flag to indicate that interactive calling is permitted. Its argument
controls the reading of arguments for an interactive call.
interactive
This section describes how to write the interactive form that
makes a Lisp function an interactively-callable command.
A command may be called from Lisp programs like any other function, but then the caller supplies the arguments and arg-descriptor has no effect.
The interactive form has its effect because the command loop
(actually, its subroutine call-interactively) scans through the
function definition looking for it, before calling the function. Once
the function is called, all its body forms including the
interactive form are executed, but at this time
interactive simply returns nil without even evaluating its
argument.
There are three possibilities for the argument arg-descriptor:
nil; then the command is called with no
arguments. This leads quickly to an error if the command requires one
or more arguments.
(interactive
(list (region-beginning) (region-end)
(read-string "Foo: " nil 'my-history)))
Here's how to avoid the problem, by examining point and the mark only
after reading the keyboard input:
(interactive (let ((string (read-string "Foo: " nil 'my-history))) (list (region-beginning) (region-end) string)))
(interactive "bFrobnicate buffer: ")The code letter `b' says to read the name of an existing buffer, with completion. The buffer name is the sole argument passed to the command. The rest of the string is a prompt. If there is a newline character in the string, it terminates the prompt. If the string does not end there, then the rest of the string should contain another code character and prompt, specifying another argument. You can specify any number of arguments in this way. The prompt string can use `%' to include previous argument values (starting with the first argument) in the prompt. This is done using
format (see section Formatting Strings). For example, here is how
you could read the name of an existing buffer followed by a new name to
give to that buffer:
(interactive "bBuffer to rename: \nsRename buffer %s to: ")If the first character in the string is `*', then an error is signaled if the buffer is read-only. If the first character in the string is `@', and if the key sequence used to invoke the command includes any mouse events, then the window associated with the first of those events is selected before the command is run. You can use `*' and `@' together; the order does not matter. Actual reading of arguments is controlled by the rest of the prompt string (starting with the first character that is not `*' or `@').
interactiveThe code character descriptions below contain a number of key words, defined here as follows:
completing-read
(see section Completion). ? displays a list of possible completions.
Here are the code character descriptions for use with interactive:
fboundp). Existing,
Completion, Prompt.
commandp). Existing,
Completion, Prompt.
default-directory (see section Operating System Environment).
Existing, Completion, Default, Prompt.
default-directory. Existing, Completion, Default,
Prompt.
nil as
the argument's value. No I/O.
describe-key and
global-set-key.
user-variable-p). See section High-Level Completion Functions. Existing,
Completion, Prompt.
nil. See section Coding Systems. Completion,
Existing, Prompt.
nil as the
argument value. Completion, Existing, Prompt.
interactive
Here are some examples of interactive:
(defun foo1 () ;foo1takes no arguments, (interactive) ; just moves forward two words. (forward-word 2)) => foo1 (defun foo2 (n) ;foo2takes one argument, (interactive "p") ; which is the numeric prefix. (forward-word (* 2 n))) => foo2 (defun foo3 (n) ;foo3takes one argument, (interactive "nCount:") ; which is read with the Minibuffer. (forward-word (* 2 n))) => foo3 (defun three-b (b1 b2 b3) "Select three existing buffers. Put them into three windows, selecting the last one." (interactive "bBuffer1:\nbBuffer2:\nbBuffer3:") (delete-other-windows) (split-window (selected-window) 8) (switch-to-buffer b1) (other-window 1) (split-window (selected-window) 8) (switch-to-buffer b2) (other-window 1) (switch-to-buffer b3)) => three-b (three-b "*scratch*" "declarations.texi" "*mail*") => nil
After the command loop has translated a key sequence into a command it
invokes that command using the function command-execute. If the
command is a function, command-execute calls
call-interactively, which reads the arguments and calls the
command. You can also call these functions yourself.
t if object is suitable for calling interactively;
that is, if object is a command. Otherwise, returns nil.
The interactively callable objects include strings and vectors (treated
as keyboard macros), lambda expressions that contain a top-level call to
interactive, byte-code function objects made from such lambda
expressions, autoload objects that are declared as interactive
(non-nil fourth argument to autoload), and some of the
primitive functions.
A symbol satisfies commandp if its function definition satisfies
commandp.
Keys and keymaps are not commands. Rather, they are used to look up commands (see section Keymaps).
See documentation in section Access to Documentation Strings, for a
realistic example of using commandp.
If record-flag is non-nil, then this command and its
arguments are unconditionally added to the list command-history.
Otherwise, the command is added only if it uses the minibuffer to read
an argument. See section Command History.
The argument keys, if given, specifies the sequence of events to supply if the command inquires which events were used to invoke it.
commandp predicate; i.e., it must be an interactively
callable function or a keyboard macro.
A string or vector as command is executed with
execute-kbd-macro. A function is passed to
call-interactively, along with the optional record-flag.
A symbol is handled by using its function definition in its place. A
symbol with an autoload definition counts as a command if it was
declared to stand for an interactively callable function. Such a
definition is handled by loading the specified library and then
rechecking the definition of the symbol.
The argument keys, if given, specifies the sequence of events to supply if the command inquires which events were used to invoke it.
completing-read (see section Completion). Then it uses
command-execute to call the specified command. Whatever that
command returns becomes the value of execute-extended-command.
If the command asks for a prefix argument, it receives the value
prefix-argument. If execute-extended-command is called
interactively, the current raw prefix argument is used for
prefix-argument, and thus passed on to whatever command is run.
execute-extended-command is the normal definition of M-x,
so it uses the string `M-x ' as a prompt. (It would be better
to take the prompt from the events used to invoke
execute-extended-command, but that is painful to implement.) A
description of the value of the prefix argument, if any, also becomes
part of the prompt.
(execute-extended-command 1)
---------- Buffer: Minibuffer ----------
1 M-x forward-word RET
---------- Buffer: Minibuffer ----------
=> t
t if the containing function (the one whose
code includes the call to interactive-p) was called
interactively, with the function call-interactively. (It makes
no difference whether call-interactively was called from Lisp or
directly from the editor command loop.) If the containing function was
called by Lisp evaluation (or with apply or funcall), then
it was not called interactively.
The most common use of interactive-p is for deciding whether to
print an informative message. As a special exception,
interactive-p returns nil whenever a keyboard macro is
being run. This is to suppress the informative messages and speed
execution of the macro.
For example:
(defun foo ()
(interactive)
(when (interactive-p)
(message "foo")))
=> foo
(defun bar ()
(interactive)
(setq foobar (list (foo) (interactive-p))))
=> bar
;; Type M-x foo.
-| foo
;; Type M-x bar.
;; This does not print anything.
foobar
=> (nil t)
The other way to do this sort of job is to make the command take an
argument print-message which should be non-nil in an
interactive call, and use the interactive spec to make sure it is
non-nil. Here's how:
(defun foo (&optional print-message)
(interactive "p")
(when print-message
(message "foo")))
The numeric prefix argument, provided by `p', is never nil.
The editor command loop sets several Lisp variables to keep status records for itself and for commands that are run.
The value is copied from this-command when a command returns to
the command loop, except when the command has specified a prefix
argument for the following command.
This variable is always local to the current terminal and cannot be buffer-local. See section Multiple Displays.
last-command,
but never altered by Lisp programs.
last-command, it is normally a symbol
with a function definition.
The command loop sets this variable just before running a command, and
copies its value into last-command when the command finishes
(unless the command specified a prefix argument for the following
command).
Some commands set this variable during their execution, as a flag for
whatever command runs next. In particular, the functions for killing text
set this-command to kill-region so that any kill commands
immediately following will know to append the killed text to the
previous kill.
If you do not want a particular command to be recognized as the previous
command in the case where it got an error, you must code that command to
prevent this. One way is to set this-command to t at the
beginning of the command, and set this-command back to its proper
value at the end, like this:
(defun foo (args...)
(interactive ...)
(let ((old-this-command this-command))
(setq this-command t)
...do the work...
(setq this-command old-this-command)))
We do not bind this-command with let because that would
restore the old value in case of error--a feature of let which
in this case does precisely what we want to avoid.
(this-command-keys)
;; Now use C-u C-x C-e to evaluate that.
=> "^U^X^E"
this-command-keys, except that it always returns
the events in a vector, so you do never need to deal with the complexities
of storing input events in a string (see section Putting Keyboard Events in Strings).
One use of this variable is for telling x-popup-menu where to pop
up a menu. It is also used internally by y-or-n-p
(see section Yes-or-No Queries).
self-insert-command, which uses it to decide which
character to insert.
last-command-event
;; Now use C-u C-x C-e to evaluate that.
=> 5
The value is 5 because that is the ASCII code for C-e.
The alias last-command-char exists for compatibility with
Emacs version 18.
The Emacs command loop reads a sequence of input events that represent keyboard or mouse activity. The events for keyboard activity are characters or symbols; mouse events are always lists. This section describes the representation and meaning of input events in detail.
nil if object is an input event
or event type.
Note that any symbol might be used as an event or an event type.
eventp cannot distinguish whether a symbol is intended by Lisp
code to be used as an event. Instead, it distinguishes whether the
symbol has actually been used in an event that has been read as input in
the current Emacs session. If a symbol has not yet been so used,
eventp returns nil.
There are two kinds of input you can get from the keyboard: ordinary keys, and function keys. Ordinary keys correspond to characters; the events they generate are represented in Lisp as characters. The event type of a character event is the character itself (an integer); see section Classifying Events.
An input character event consists of a basic code between 0 and 524287, plus any or all of these modifier bits:
It is best to avoid mentioning specific bit numbers in your program.
To test the modifier bits of a character, use the function
event-modifiers (see section Classifying Events). When making key
bindings, you can use the read syntax for characters with modifier bits
(`\C-', `\M-', and so on). For making key bindings with
define-key, you can use lists such as (control hyper ?x) to
specify the characters (see section Changing Key Bindings). The function
event-convert-list converts such a list into an event type
(see section Classifying Events).
Most keyboards also have function keys---keys that have names or
symbols that are not characters. Function keys are represented in Emacs
Lisp as symbols; the symbol's name is the function key's label, in lower
case. For example, pressing a key labeled F1 places the symbol
f1 in the input stream.
The event type of a function key event is the event symbol itself. See section Classifying Events.
Here are a few special cases in the symbol-naming convention for function keys:
backspace, tab, newline, return, delete
tab.
Most of the time, it's not useful to distinguish the two. So normally
function-key-map (see section Translating Input Events) is set up to map
tab into 9. Thus, a key binding for character code 9 (the
character C-i) also applies to tab. Likewise for the other
symbols in this group. The function read-char likewise converts
these events into characters.
In ASCII, BS is really C-h. But backspace
converts into the character code 127 (DEL), not into code 8
(BS). This is what most users prefer.
left, up, right, down
kp-add, kp-decimal, kp-divide, ...
kp-0, kp-1, ...
kp-f1, kp-f2, kp-f3, kp-f4
kp-home, kp-left, kp-up, kp-right, kp-down
home, left, ...
kp-prior, kp-next, kp-end, kp-begin, kp-insert, kp-delete
You can use the modifier keys ALT, CTRL, HYPER, META, SHIFT, and SUPER with function keys. The way to represent them is with prefixes in the symbol name:
Thus, the symbol for the key F3 with META held down is
M-f3. When you use more than one prefix, we recommend you
write them in alphabetical order; but the order does not matter in
arguments to the key-binding lookup and modification functions.
Emacs supports four kinds of mouse events: click events, drag events, button-down events, and motion events. All mouse events are represented as lists. The CAR of the list is the event type; this says which mouse button was involved, and which modifier keys were used with it. The event type can also distinguish double or triple button presses (see section Repeat Events). The rest of the list elements give position and time information.
For key lookup, only the event type matters: two events of the same type
necessarily run the same command. The command can access the full
values of these events using the `e' interactive code.
See section Code Characters for interactive.
A key sequence that starts with a mouse event is read using the keymaps of the buffer in the window that the mouse was in, not the current buffer. This does not imply that clicking in a window selects that window or its buffer--that is entirely under the control of the command binding of the key sequence.
When the user presses a mouse button and releases it at the same location, that generates a click event. Mouse click events have this form:
(event-type (window buffer-pos (x . y) timestamp) click-count)
Here is what the elements normally mean:
mouse-1, mouse-2, ..., where the
buttons are numbered left to right.
You can also use prefixes `A-', `C-', `H-', `M-',
`S-' and `s-' for modifiers alt, control, hyper, meta, shift
and super, just as you would with function keys.
This symbol also serves as the event type of the event. Key bindings
describe events by their types; thus, if there is a key binding for
mouse-1, that binding would apply to all events whose
event-type is mouse-1.
(0 . 0).
The meanings of buffer-pos, x and y are somewhat different when the event location is in a special part of the screen, such as the mode line or a scroll bar.
If the location is in a scroll bar, then buffer-pos is the symbol
vertical-scroll-bar or horizontal-scroll-bar, and the pair
(x . y) is replaced with a pair (portion
. whole), where portion is the distance of the click from
the top or left end of the scroll bar, and whole is the length of
the entire scroll bar.
If the position is on a mode line or the vertical line separating
window from its neighbor to the right, then buffer-pos is
the symbol mode-line or vertical-line. For the mode line,
y does not have meaningful data. For the vertical line, x
does not have meaningful data.
In one special case, buffer-pos is a list containing a symbol (one of the symbols listed above) instead of just the symbol. This happens after the imaginary prefix keys for the event are inserted into the input stream. See section Key Sequence Input.
With Emacs, you can have a drag event without even changing your clothes. A drag event happens every time the user presses a mouse button and then moves the mouse to a different character position before releasing the button. Like all mouse events, drag events are represented in Lisp as lists. The lists record both the starting mouse position and the final position, like this:
(event-type (window1 buffer-pos1 (x1 . y1) timestamp1) (window2 buffer-pos2 (x2 . y2) timestamp2) click-count)
For a drag event, the name of the symbol event-type contains the
prefix `drag-'. For example, dragging the mouse with button 2 held
down generates a drag-mouse-2 event. The second and third
elements of the event give the starting and ending position of the drag.
Aside from that, the data have the same meanings as in a click event
(see section Click Events). You can access the second element of any mouse
event in the same way, with no need to distinguish drag events from
others.
The `drag-' prefix follows the modifier key prefixes such as `C-' and `M-'.
If read-key-sequence receives a drag event that has no key
binding, and the corresponding click event does have a binding, it
changes the drag event into a click event at the drag's starting
position. This means that you don't have to distinguish between click
and drag events unless you want to.
Click and drag events happen when the user releases a mouse button. They cannot happen earlier, because there is no way to distinguish a click from a drag until the button is released.
If you want to take action as soon as a button is pressed, you need to handle button-down events.(3) These occur as soon as a button is pressed. They are represented by lists that look exactly like click events (see section Click Events), except that the event-type symbol name contains the prefix `down-'. The `down-' prefix follows modifier key prefixes such as `C-' and `M-'.
The function read-key-sequence ignores any button-down events
that don't have command bindings; therefore, the Emacs command loop
ignores them too. This means that you need not worry about defining
button-down events unless you want them to do something. The usual
reason to define a button-down event is so that you can track mouse
motion (by reading motion events) until the button is released.
See section Motion Events.
If you press the same mouse button more than once in quick succession without moving the mouse, Emacs generates special repeat mouse events for the second and subsequent presses.
The most common repeat events are double-click events. Emacs generates a double-click event when you click a button twice; the event happens when you release the button (as is normal for all click events).
The event type of a double-click event contains the prefix
`double-'. Thus, a double click on the second mouse button with
meta held down comes to the Lisp program as
M-double-mouse-2. If a double-click event has no binding, the
binding of the corresponding ordinary click event is used to execute
it. Thus, you need not pay attention to the double click feature
unless you really want to.
When the user performs a double click, Emacs generates first an ordinary click event, and then a double-click event. Therefore, you must design the command binding of the double click event to assume that the single-click command has already run. It must produce the desired results of a double click, starting from the results of a single click.
This is convenient, if the meaning of a double click somehow "builds on" the meaning of a single click--which is recommended user interface design practice for double clicks.
If you click a button, then press it down again and start moving the mouse with the button held down, then you get a double-drag event when you ultimately release the button. Its event type contains `double-drag' instead of just `drag'. If a double-drag event has no binding, Emacs looks for an alternate binding as if the event were an ordinary drag.
Before the double-click or double-drag event, Emacs generates a double-down event when the user presses the button down for the second time. Its event type contains `double-down' instead of just `down'. If a double-down event has no binding, Emacs looks for an alternate binding as if the event were an ordinary button-down event. If it finds no binding that way either, the double-down event is ignored.
To summarize, when you click a button and then press it again right away, Emacs generates a down event and a click event for the first click, a double-down event when you press the button again, and finally either a double-click or a double-drag event.
If you click a button twice and then press it again, all in quick succession, Emacs generates a triple-down event, followed by either a triple-click or a triple-drag. The event types of these events contain `triple' instead of `double'. If any triple event has no binding, Emacs uses the binding that it would use for the corresponding double event.
If you click a button three or more times and then press it again, the events for the presses beyond the third are all triple events. Emacs does not have separate event types for quadruple, quintuple, etc. events. However, you can look at the event list to find out precisely how many times the button was pressed.
double-click-time. Setting double-click-time to
nil disables multi-click detection entirely. Setting it to
t removes the time limit; Emacs then detects multi-clicks by
position only.
Emacs sometimes generates mouse motion events to describe motion of the mouse without any button activity. Mouse motion events are represented by lists that look like this:
(mouse-movement (window buffer-pos (x . y) timestamp))
The second element of the list describes the current position of the mouse, just as in a click event (see section Click Events).
The special form track-mouse enables generation of motion events
within its body. Outside of track-mouse forms, Emacs does not
generate events for mere motion of the mouse, and these events do not
appear. See section Mouse Tracking.
Window systems provide general ways for the user to control which window gets keyboard input. This choice of window is called the focus. When the user does something to switch between Emacs frames, that generates a focus event. The normal definition of a focus event, in the global keymap, is to select a new frame within Emacs, as the user would expect. See section Input Focus.
Focus events are represented in Lisp as lists that look like this:
(switch-frame new-frame)
where new-frame is the frame switched to.
Most X window managers are set up so that just moving the mouse into a window is enough to set the focus there. Emacs appears to do this, because it changes the cursor to solid in the new frame. However, there is no need for the Lisp program to know about the focus change until some other kind of input arrives. So Emacs generates a focus event only when the user actually types a keyboard key or presses a mouse button in the new frame; just moving the mouse between frames does not generate a focus event.
A focus event in the middle of a key sequence would garble the sequence. So Emacs never generates a focus event in the middle of a key sequence. If the user changes focus in the middle of a key sequence--that is, after a prefix key--then Emacs reorders the events so that the focus event comes either before or after the multi-event key sequence, and not within it.
A few other event types represent occurrences within the window system.
(delete-frame (frame))
delete-frame event is to delete frame.
(iconify-frame (frame))
ignore; since the
frame has already been iconified, Emacs has no work to do. The purpose
of this event type is so that you can keep track of such events if you
want to.
(make-frame-visible (frame))
ignore; since the
frame has already been made visible, Emacs has no work to do.
(mouse-wheel position delta)
(drag-n-drop position files)
If one of these events arrives in the middle of a key sequence--that is, after a prefix key--then Emacs reorders the events so that this event comes either before or after the multi-event key sequence, not within it.
If the user presses and releases the left mouse button over the same location, that generates a sequence of events like this:
(down-mouse-1 (#<window 18 on NEWS> 2613 (0 . 38) -864320)) (mouse-1 (#<window 18 on NEWS> 2613 (0 . 38) -864180))
While holding the control key down, the user might hold down the second mouse button, and drag the mouse from one line to the next. That produces two events, as shown here:
(C-down-mouse-2 (#<window 18 on NEWS> 3440 (0 . 27) -731219))
(C-drag-mouse-2 (#<window 18 on NEWS> 3440 (0 . 27) -731219)
(#<window 18 on NEWS> 3510 (0 . 28) -729648))
While holding down the meta and shift keys, the user might press the second mouse button on the window's mode line, and then drag the mouse into another window. That produces a pair of events like these:
(M-S-down-mouse-2 (#<window 18 on NEWS> mode-line (33 . 31) -457844))
(M-S-drag-mouse-2 (#<window 18 on NEWS> mode-line (33 . 31) -457844)
(#<window 20 on carlton-sanskrit.tex> 161 (33 . 3)
-453816))
Every event has an event type, which classifies the event for key binding purposes. For a keyboard event, the event type equals the event value; thus, the event type for a character is the character, and the event type for a function key symbol is the symbol itself. For events that are lists, the event type is the symbol in the CAR of the list. Thus, the event type is always a symbol or a character.
Two events of the same type are equivalent where key bindings are concerned; thus, they always run the same command. That does not necessarily mean they do the same things, however, as some commands look at the whole event to decide what to do. For example, some commands use the location of a mouse event to decide where in the buffer to act.
Sometimes broader classifications of events are useful. For example, you might want to ask whether an event involved the META key, regardless of which other key or mouse button was used.
The functions event-modifiers and event-basic-type are
provided to get such information conveniently.
shift, control,
meta, alt, hyper and super. In addition,
the modifiers list of a mouse event symbol always contains one of
click, drag, and down.
The argument event may be an entire event object, or just an event type.
Here are some examples:
(event-modifiers ?a)
=> nil
(event-modifiers ?\C-a)
=> (control)
(event-modifiers ?\C-%)
=> (control)
(event-modifiers ?\C-\S-a)
=> (control shift)
(event-modifiers 'f5)
=> nil
(event-modifiers 's-f5)
=> (super)
(event-modifiers 'M-S-f5)
=> (meta shift)
(event-modifiers 'mouse-1)
=> (click)
(event-modifiers 'down-mouse-1)
=> (down)
The modifiers list for a click event explicitly contains click,
but the event symbol name itself does not contain `click'.
(event-basic-type ?a)
=> 97
(event-basic-type ?A)
=> 97
(event-basic-type ?\C-a)
=> 97
(event-basic-type ?\C-\S-a)
=> 97
(event-basic-type 'f5)
=> f5
(event-basic-type 's-f5)
=> f5
(event-basic-type 'M-S-f5)
=> f5
(event-basic-type 'down-mouse-1)
=> mouse-1
nil if object is a mouse movement
event.
(event-convert-list '(control ?a))
=> 1
(event-convert-list '(control meta ?a))
=> -134217727
(event-convert-list '(control super f1))
=> C-s-f1
This section describes convenient functions for accessing the data in a mouse button or motion event.
These two functions return the starting or ending position of a mouse-button event, as a list of this form:
(window buffer-position (x . y) timestamp)
If event is a click or button-down event, this returns the location of the event. If event is a drag event, this returns the drag's starting position.
If event is a drag event, this returns the position where the user released the mouse button. If event is a click or button-down event, the value is actually the starting position, which is the only position such events have.
These five functions take a position list as described above, and return various parts of it.
(x . y).
(col . row). These are computed from the
x and y values actually found in position.
These functions are useful for decoding scroll bar events.
(portion . whole) containing two integers whose ratio
is the fractional position.
(num . denom)---typically a
value returned by scroll-bar-event-ratio.
This function is handy for scaling a position on a scroll bar into a buffer position. Here's how to do that:
(+ (point-min)
(scroll-bar-scale
(posn-x-y (event-start event))
(- (point-max) (point-min))))
Recall that scroll bar events have two integers forming a ratio, in place of a pair of x and y coordinates.
In most of the places where strings are used, we conceptualize the string as containing text characters--the same kind of characters found in buffers or files. Occasionally Lisp programs use strings that conceptually contain keyboard characters; for example, they may be key sequences or keyboard macro definitions. However, storing keyboard characters in a string is a complex matter, for reasons of historical compatibility, and it is not always possible.
We recommend that new programs avoid dealing with these complexities by not storing keyboard events in strings. Here is how to do that:
lookup-key and
define-key. For example, you can use
read-key-sequence-vector instead of read-key-sequence, and
this-command-keys-vector instead of this-command-keys.
define-key.
listify-key-sequence (see section Miscellaneous Event Input Features)
first, to convert it to a list.
The complexities stem from the modifier bits that keyboard input characters can include. Aside from the Meta modifier, none of these modifier bits can be included in a string, and the Meta modifier is allowed only in special cases.
The earliest GNU Emacs versions represented meta characters as codes
in the range of 128 to 255. At that time, the basic character codes
ranged from 0 to 127, so all keyboard character codes did fit in a
string. Many Lisp programs used `\M-' in string constants to stand
for meta characters, especially in arguments to define-key and
similar functions, and key sequences and sequences of events were always
represented as strings.
When we added support for larger basic character codes beyond 127, and additional modifier bits, we had to change the representation of meta characters. Now the flag that represents the Meta modifier in a character is and such numbers cannot be included in a string.
To support programs with `\M-' in string constants, there are special rules for including certain meta characters in a string. Here are the rules for interpreting a string as a sequence of input characters:
Functions such as read-key-sequence that construct strings of
keyboard input characters follow these rules: they construct vectors
instead of strings, when the events won't fit in a string.
When you use the read syntax `\M-' in a string, it produces a code in the range of 128 to 255--the same code that you get if you modify the corresponding keyboard event to put it in the string. Thus, meta events in strings work consistently regardless of how they get into the strings.
However, most programs would do well to avoid these issues by following the recommendations at the beginning of this section.
The editor command loop reads key sequences using the function
read-key-sequence, which uses read-event. These and other
functions for event input are also available for use in Lisp programs.
See also momentary-string-display in section Temporary Displays,
and sit-for in section Waiting for Elapsed Time or Input. See section Terminal Input, for
functions and variables for controlling terminal input modes and
debugging terminal input. See section Translating Input Events, for features you
can use for translating or modifying input events while reading them.
For higher-level input facilities, see section Minibuffers.
The command loop reads input a key sequence at a time, by calling
read-key-sequence. Lisp programs can also call this function;
for example, describe-key uses it to read the key to describe.
If the events are all characters and all can fit in a string, then
read-key-sequence returns a string (see section Putting Keyboard Events in Strings).
Otherwise, it returns a vector, since a vector can hold all kinds of
events--characters, symbols, and lists. The elements of the string or
vector are the events in the key sequence.
The argument prompt is either a string to be displayed in the echo
area as a prompt, or nil, meaning not to display a prompt.
In the example below, the prompt `?' is displayed in the echo area, and the user types C-x C-f.
(read-key-sequence "?")
---------- Echo Area ----------
?C-x C-f
---------- Echo Area ----------
=> "^X^F"
The function read-key-sequence suppresses quitting: C-g
typed while reading with this function works like any other character,
and does not set quit-flag. See section Quitting.
read-key-sequence except that it always
returns the key sequence as a vector, never as a string.
See section Putting Keyboard Events in Strings.
If an input character is an upper-case letter and has no key binding,
but its lower-case equivalent has one, then read-key-sequence
converts the character to lower case. Note that lookup-key does
not perform case conversion in this way.
The function read-key-sequence also transforms some mouse events.
It converts unbound drag events into click events, and discards unbound
button-down events entirely. It also reshuffles focus events and
miscellaneous window events so that they never appear in a key sequence
with any other events.
When mouse events occur in special parts of a window, such as a mode
line or a scroll bar, the event type shows nothing special--it is the
same symbol that would normally represent that combination of mouse
button and modifier keys. The information about the window part is kept
elsewhere in the event--in the coordinates. But
read-key-sequence translates this information into imaginary
"prefix keys", all of which are symbols: mode-line,
vertical-line, horizontal-scroll-bar and
vertical-scroll-bar. You can define meanings for mouse clicks in
special window parts by defining key sequences using these imaginary
prefix keys.
For example, if you call read-key-sequence and then click the
mouse on the window's mode line, you get two events, like this:
(read-key-sequence "Click on the mode line: ")
=> [mode-line
(mouse-1
(#<window 6 on NEWS> mode-line
(40 . 63) 5959987))]
The lowest level functions for command input are those that read a single event.
If prompt is non-nil, it should be a string to display in
the echo area as a prompt. Otherwise, read-event does not
display any message to indicate it is waiting for input; instead, it
prompts by echoing: it displays descriptions of the events that led to
or were read by the current command. See section The Echo Area.
If suppress-input-method is non-nil, then the current input
method is disabled for reading this event. If you want to read an event
without input-method processing, always do it this way; don't try binding
input-method-function (see below).
If cursor-in-echo-area is non-nil, then read-event
moves the cursor temporarily to the echo area, to the end of any message
displayed there. Otherwise read-event does not move the cursor.
If read-event gets an event that is defined as a help character, in
some cases read-event processes the event directly without
returning. See section Help Functions. Certain other events, called
special events, are also processed directly within
read-event (see section Special Events).
Here is what happens if you call read-event and then press the
right-arrow function key:
(read-event)
=> right
In the first example, the user types the character 1 (ASCII
code 49). The second example shows a keyboard macro definition that
calls read-char from the minibuffer using eval-expression.
read-char reads the keyboard macro's very next character, which
is 1. Then eval-expression displays its return value in
the echo area.
(read-char)
=> 49
;; We assume here you use M-: to evaluate this.
(symbol-function 'foo)
=> "^[:(read-char)^M1"
(execute-kbd-macro 'foo)
-| 49
=> nil
read-event also invokes the current input method, if any. If
the value of input-method-function is non-nil, it should
be a function; when read-event reads a printing character
(including SPC) with no modifier bits, it calls that function,
passing the event as an argument.
nil, its value specifies the current input method
function.
Note: Don't bind this variable with let. It is often
buffer-local, and if you bind it around reading input (which is exactly
when you would bind it), switching buffers asynchronously while
Emacs is waiting will cause the value to be restored in the wrong
buffer.
The input method function should return a list of events which should
be used as input. (If the list is nil, that means there is no
input, so read-event waits for another event.) These events are
processed before the events in unread-command-events. Events
returned by the input method function are not passed to the input method
function again, even if they are printing characters with no modifier
bits.
If the input method function calls read-event or
read-key-sequence, it should bind input-method-function to
nil first, to prevent recursion.
The input method function is not called when reading the second and
subsequent event of a key sequence. Thus, these characters are not
subject to input method processing. It is usually a good idea for the
input method processing to test the values of
overriding-local-map and overriding-terminal-local-map; if
either of these variables is non-nil, the input method should put
its argument into a list and return that list with no further
processing.
You can use the function read-quoted-char to ask the user to
specify a character, and allow the user to specify a control or meta
character conveniently, either literally or as an octal character code.
The command quoted-insert uses this function.
read-char, except that if the first
character read is an octal digit (0-7), it reads any number of octal
digits (but stopping if a non-octal digit is found), and returns the
character represented by that numeric character code.
Quitting is suppressed when the first character is read, so that the user can enter a C-g. See section Quitting.
If prompt is supplied, it specifies a string for prompting the user. The prompt string is always displayed in the echo area, followed by a single `-'.
In the following example, the user types in the octal number 177 (which is 127 in decimal).
(read-quoted-char "What character")
---------- Echo Area ----------
What character-177
---------- Echo Area ----------
=> 127
This section describes how to "peek ahead" at events without using
them up, how to check for pending input, and how to discard pending
input. See also the function read-passwd (see section Reading a Password).
The variable is needed because in some cases a function reads an event and then decides not to use it. Storing the event in this variable causes it to be processed normally, by the command loop or by the functions to read command input.
For example, the function that implements numeric prefix arguments reads any number of digits. When it finds a non-digit event, it must unread the event so that it can be read normally by the command loop. Likewise, incremental search uses this feature to unread events with no special meaning in a search, because these events should exit the search and then execute normally.
The reliable and easy way to extract events from a key sequence so as to
put them in unread-command-events is to use
listify-key-sequence (see section Putting Keyboard Events in Strings).
Normally you add events to the front of this list, so that the events most recently unread will be reread first.
unread-command-events.
This variable is mostly obsolete now that you can use
unread-command-events instead; it exists only to support programs
written for Emacs versions 18 and earlier.
t if
there is available input, nil otherwise. On rare occasions it
may return t when no input is available.
In the example below, the Lisp program reads the character 1,
ASCII code 49. It becomes the value of last-input-event,
while C-e (we assume C-x C-e command is used to evaluate
this expression) remains the value of last-command-event.
(progn (print (read-char))
(print last-command-event)
last-input-event)
-| 49
-| 5
=> 49
The alias last-input-char exists for compatibility with
Emacs version 18.
nil.
In the following example, the user may type a number of characters right
after starting the evaluation of the form. After the sleep-for
finishes sleeping, discard-input discards any characters typed
during the sleep.
(progn (sleep-for 2)
(discard-input))
=> nil
Special events are handled at a very low level--as soon as they are
read. The read-event function processes these events itself, and
never returns them.
Events that are handled in this way do not echo, they are never grouped
into key sequences, and they never appear in the value of
last-command-event or (this-command-keys). They do not
discard a numeric argument, they cannot be unread with
unread-command-events, they may not appear in a keyboard macro,
and they are not recorded in a keyboard macro while you are defining
one.
These events do, however, appear in last-input-event immediately
after they are read, and this is the way for the event's definition to
find the actual event.
The events types iconify-frame, make-frame-visible and
delete-frame are normally handled in this way. The keymap which
defines how to handle special events--and which events are special--is
in the variable special-event-map (see section Active Keymaps).
The wait functions are designed to wait for a certain amount of time
to pass or until there is input. For example, you may wish to pause in
the middle of a computation to allow the user time to view the display.
sit-for pauses and updates the screen, and returns immediately if
input comes in, while sleep-for pauses without updating the
screen.
t if sit-for waited the full
time with no input arriving (see input-pending-p in section Miscellaneous Event Input Features). Otherwise, the value is nil.
The argument seconds need not be an integer. If it is a floating
point number, sit-for waits for a fractional number of seconds.
Some systems support only a whole number of seconds; on these systems,
seconds is rounded down.
The optional argument millisec specifies an additional waiting period measured in milliseconds. This adds to the period specified by seconds. If the system doesn't support waiting fractions of a second, you get an error if you specify nonzero millisec.
Redisplay is always preempted if input arrives, and does not happen at
all if input is available before it starts. Thus, there is no way to
force screen updating if there is pending input; however, if there is no
input pending, you can force an update with no delay by using
(sit-for 0).
If nodisp is non-nil, then sit-for does not
redisplay, but it still returns as soon as input is available (or when
the timeout elapses).
Iconifying or deiconifying a frame makes sit-for return, because
that generates an event. See section Miscellaneous Window System Events.
The usual purpose of sit-for is to give the user time to read
text that you display.
nil.
The argument seconds need not be an integer. If it is a floating
point number, sleep-for waits for a fractional number of seconds.
Some systems support only a whole number of seconds; on these systems,
seconds is rounded down.
The optional argument millisec specifies an additional waiting period measured in milliseconds. This adds to the period specified by seconds. If the system doesn't support waiting fractions of a second, you get an error if you specify nonzero millisec.
Use sleep-for when you wish to guarantee a delay.
See section Time of Day, for functions to get the current time.
Typing C-g while a Lisp function is running causes Emacs to quit whatever it is doing. This means that control returns to the innermost active command loop.
Typing C-g while the command loop is waiting for keyboard input
does not cause a quit; it acts as an ordinary input character. In the
simplest case, you cannot tell the difference, because C-g
normally runs the command keyboard-quit, whose effect is to quit.
However, when C-g follows a prefix key, they combine to form an
undefined key. The effect is to cancel the prefix key as well as any
prefix argument.
In the minibuffer, C-g has a different definition: it aborts out of the minibuffer. This means, in effect, that it exits the minibuffer and then quits. (Simply quitting would return to the command loop within the minibuffer.) The reason why C-g does not quit directly when the command reader is reading input is so that its meaning can be redefined in the minibuffer in this way. C-g following a prefix key is not redefined in the minibuffer, and it has its normal effect of canceling the prefix key and prefix argument. This too would not be possible if C-g always quit directly.
When C-g does directly quit, it does so by setting the variable
quit-flag to t. Emacs checks this variable at appropriate
times and quits if it is not nil. Setting quit-flag
non-nil in any way thus causes a quit.
At the level of C code, quitting cannot happen just anywhere; only at the
special places that check quit-flag. The reason for this is
that quitting at other places might leave an inconsistency in Emacs's
internal state. Because quitting is delayed until a safe place, quitting
cannot make Emacs crash.
Certain functions such as read-key-sequence or
read-quoted-char prevent quitting entirely even though they wait
for input. Instead of quitting, C-g serves as the requested
input. In the case of read-key-sequence, this serves to bring
about the special behavior of C-g in the command loop. In the
case of read-quoted-char, this is so that C-q can be used
to quote a C-g.
You can prevent quitting for a portion of a Lisp function by binding
the variable inhibit-quit to a non-nil value. Then,
although C-g still sets quit-flag to t as usual, the
usual result of this--a quit--is prevented. Eventually,
inhibit-quit will become nil again, such as when its
binding is unwound at the end of a let form. At that time, if
quit-flag is still non-nil, the requested quit happens
immediately. This behavior is ideal when you wish to make sure that
quitting does not happen within a "critical section" of the program.
In some functions (such as read-quoted-char), C-g is
handled in a special way that does not involve quitting. This is done
by reading the input with inhibit-quit bound to t, and
setting quit-flag to nil before inhibit-quit
becomes nil again. This excerpt from the definition of
read-quoted-char shows how this is done; it also shows that
normal quitting is permitted after the first character of input.
(defun read-quoted-char (&optional prompt)
"...documentation..."
(let ((message-log-max nil) done (first t) (code 0) char)
(while (not done)
(let ((inhibit-quit first)
...)
(and prompt (message "%s-" prompt))
(setq char (read-event))
(if inhibit-quit (setq quit-flag nil)))
...set the variable code...)
code))
nil, then Emacs quits immediately, unless
inhibit-quit is non-nil. Typing C-g ordinarily sets
quit-flag non-nil, regardless of inhibit-quit.
quit-flag
is set to a value other than nil. If inhibit-quit is
non-nil, then quit-flag has no special effect.
quit condition with (signal 'quit
nil). This is the same thing that quitting does. (See signal
in section Errors.)
You can specify a character other than C-g to use for quitting.
See the function set-input-mode in section Terminal Input.
Most Emacs commands can use a prefix argument, a number
specified before the command itself. (Don't confuse prefix arguments
with prefix keys.) The prefix argument is at all times represented by a
value, which may be nil, meaning there is currently no prefix
argument. Each command may use the prefix argument or ignore it.
There are two representations of the prefix argument: raw and numeric. The editor command loop uses the raw representation internally, and so do the Lisp variables that store the information, but commands can request either representation.
Here are the possible values of a raw prefix argument:
nil, meaning there is no prefix argument. Its numeric value is
1, but numerous commands make a distinction between nil and the
integer 1.
-. This indicates that M-- or C-u - was
typed, without following digits. The equivalent numeric value is
-1, but some commands make a distinction between the integer
-1 and the symbol -.
We illustrate these possibilities by calling the following function with various prefixes:
(defun display-prefix (arg) "Display the value of the raw prefix arg." (interactive "P") (message "%s" arg))
Here are the results of calling display-prefix with various
raw prefix arguments:
M-x display-prefix -| nil
C-u M-x display-prefix -| (4)
C-u C-u M-x display-prefix -| (16)
C-u 3 M-x display-prefix -| 3
M-3 M-x display-prefix -| 3 ; (Same as C-u 3.)
C-u - M-x display-prefix -| -
M-- M-x display-prefix -| - ; (Same as C-u -.)
C-u - 7 M-x display-prefix -| -7
M-- 7 M-x display-prefix -| -7 ; (Same as C-u -7.)
Emacs uses two variables to store the prefix argument:
prefix-arg and current-prefix-arg. Commands such as
universal-argument that set up prefix arguments for other
commands store them in prefix-arg. In contrast,
current-prefix-arg conveys the prefix argument to the current
command, so setting it has no effect on the prefix arguments for future
commands.
Normally, commands specify which representation to use for the prefix
argument, either numeric or raw, in the interactive declaration.
(See section Using interactive.) Alternatively, functions may look at the
value of the prefix argument directly in the variable
current-prefix-arg, but this is less clean.
nil, the value 1 is returned; if it is -, the
value -1 is returned; if it is a number, that number is returned;
if it is a list, the CAR of that list (which should be a number) is
returned.
(interactive "P").
universal-argument
that specify prefix arguments for the following command work by setting
this variable.
The following commands exist to set up prefix arguments for the following command. Do not call them for any other reason.
The Emacs command loop is entered automatically when Emacs starts up. This top-level invocation of the command loop never exits; it keeps running as long as Emacs does. Lisp programs can also invoke the command loop. Since this makes more than one activation of the command loop, we call it recursive editing. A recursive editing level has the effect of suspending whatever command invoked it and permitting the user to do arbitrary editing before resuming that command.
The commands available during recursive editing are the same ones available in the top-level editing loop and defined in the keymaps. Only a few special commands exit the recursive editing level; the others return to the recursive editing level when they finish. (The special commands for exiting are always available, but they do nothing when recursive editing is not in progress.)
All command loops, including recursive ones, set up all-purpose error handlers so that an error in a command run from the command loop will not exit the loop.
Minibuffer input is a special kind of recursive editing. It has a few special wrinkles, such as enabling display of the minibuffer and the minibuffer window, but fewer than you might suppose. Certain keys behave differently in the minibuffer, but that is only because of the minibuffer's local map; if you switch windows, you get the usual Emacs commands.
To invoke a recursive editing level, call the function
recursive-edit. This function contains the command loop; it also
contains a call to catch with tag exit, which makes it
possible to exit the recursive editing level by throwing to exit
(see section Explicit Nonlocal Exits: catch and throw). If you throw a value other than t,
then recursive-edit returns normally to the function that called
it. The command C-M-c (exit-recursive-edit) does this.
Throwing a t value causes recursive-edit to quit, so that
control returns to the command loop one level up. This is called
aborting, and is done by C-] (abort-recursive-edit).
Most applications should not use recursive editing, except as part of using the minibuffer. Usually it is more convenient for the user if you change the major mode of the current buffer temporarily to a special major mode, which should have a command to go back to the previous mode. (The e command in Rmail uses this technique.) Or, if you wish to give the user different text to edit "recursively", create and select a new buffer in a special mode. In this mode, define a command to complete the processing and go back to the previous buffer. (The m command in Rmail does this.)
Recursive edits are useful in debugging. You can insert a call to
debug into a function definition as a sort of breakpoint, so that
you can look around when the function gets there. debug invokes
a recursive edit but also provides the other features of the debugger.
Recursive editing levels are also used when you type C-r in
query-replace or use C-x q (kbd-macro-query).
In the following example, the function simple-rec first
advances point one word, then enters a recursive edit, printing out a
message in the echo area. The user can then do any editing desired, and
then type C-M-c to exit and continue executing simple-rec.
(defun simple-rec ()
(forward-word 1)
(message "Recursive edit in progress")
(recursive-edit)
(forward-word 1))
=> simple-rec
(simple-rec)
=> nil
(throw 'exit
nil).
quit
after exiting the recursive edit. Its definition is effectively
(throw 'exit t). See section Quitting.
Disabling a command marks the command as requiring user confirmation before it can be executed. Disabling is used for commands which might be confusing to beginning users, to prevent them from using the commands by accident.
The low-level mechanism for disabling a command is to put a
non-nil disabled property on the Lisp symbol for the
command. These properties are normally set up by the user's
`.emacs' file with Lisp expressions such as this:
(put 'upcase-region 'disabled t)
For a few commands, these properties are present by default and may be removed by the `.emacs' file.
If the value of the disabled property is a string, the message
saying the command is disabled includes that string. For example:
(put 'delete-region 'disabled
"Text deleted this way cannot be yanked back!\n")
See section `Disabling' in The GNU Emacs Manual, for the details on what happens when a disabled command is invoked interactively. Disabling a command has no effect on calling it as a function from Lisp programs.
this-command-keys to determine what the user typed to run the
command, and thus find the command itself. See section Hooks.
By default, disabled-command-hook contains a function that asks
the user whether to proceed.
The command loop keeps a history of the complex commands that have
been executed, to make it convenient to repeat these commands. A
complex command is one for which the interactive argument reading
uses the minibuffer. This includes any M-x command, any
M-: command, and any command whose interactive
specification reads an argument from the minibuffer. Explicit use of
the minibuffer during the execution of the command itself does not cause
the command to be considered complex.
history-length), the oldest elements are deleted as new ones are
added.
command-history
=> ((switch-to-buffer "chistory.texi")
(describe-key "^X^[")
(visit-tags-table "~/emacs/src/")
(find-tag "repeat-complex-command"))
This history list is actually a special case of minibuffer history (see section Minibuffer History), with one special twist: the elements are expressions rather than strings.
There are a number of commands devoted to the editing and recall of
previous commands. The commands repeat-complex-command, and
list-command-history are described in the user manual
(see section `Repetition' in The GNU Emacs Manual). Within the
minibuffer, the usual minibuffer history commands are available.
A keyboard macro is a canned sequence of input events that can be considered a command and made the definition of a key. The Lisp representation of a keyboard macro is a string or vector containing the events. Don't confuse keyboard macros with Lisp macros (see section Macros).
If kbdmacro is a symbol, then its function definition is used in place of kbdmacro. If that is another symbol, this process repeats. Eventually the result should be a string or vector. If the result is not a symbol, string, or vector, an error is signaled.
The argument count is a repeat count; kbdmacro is executed that
many times. If count is omitted or nil, kbdmacro is
executed once. If it is 0, kbdmacro is executed over and over until it
encounters an error or a failing search.
See section Reading One Event, for an example of using execute-kbd-macro.
nil if no macro is
currently executing. A command can test this variable so as to behave
differently when run from an executing macro. Do not set this variable
yourself.
start-kbd-macro and
end-kbd-macro set this variable--do not set it yourself.
The variable is always local to the current terminal and cannot be buffer-local. See section Multiple Displays.
nil.
The variable is always local to the current terminal and cannot be buffer-local. See section Multiple Displays.
The bindings between input events and commands are recorded in data structures called keymaps. Each binding in a keymap associates (or binds) an individual event type either to another keymap or to a command. When an event type is bound to a keymap, that keymap is used to look up the next input event; this continues until a command is found. The whole process is called key lookup.
A keymap is a table mapping event types to definitions (which can be any Lisp objects, though only certain types are meaningful for execution by the command loop). Given an event (or an event type) and a keymap, Emacs can get the event's definition. Events include characters, function keys, and mouse actions (see section Input Events).
A sequence of input events that form a unit is called a key sequence, or key for short. A sequence of one event is always a key sequence, and so are some multi-event sequences.
A keymap determines a binding or definition for any key sequence. If the key sequence is a single event, its binding is the definition of the event in the keymap. The binding of a key sequence of more than one event is found by an iterative process: the binding of the first event is found, and must be a keymap; then the second event's binding is found in that keymap, and so on until all the events in the key sequence are used up.
If the binding of a key sequence is a keymap, we call the key sequence
a prefix key. Otherwise, we call it a complete key (because
no more events can be added to it). If the binding is nil,
we call the key undefined. Examples of prefix keys are C-c,
C-x, and C-x 4. Examples of defined complete keys are
X, RET, and C-x 4 C-f. Examples of undefined complete
keys are C-x C-g, and C-c 3. See section Prefix Keys, for more
details.
The rule for finding the binding of a key sequence assumes that the intermediate bindings (found for the events before the last) are all keymaps; if this is not so, the sequence of events does not form a unit--it is not really one key sequence. In other words, removing one or more events from the end of any valid key sequence must always yield a prefix key. For example, C-f C-n is not a key sequence; C-f is not a prefix key, so a longer sequence starting with C-f cannot be a key sequence.
The set of possible multi-event key sequences depends on the bindings for prefix keys; therefore, it can be different for different keymaps, and can change when bindings are changed. However, a one-event sequence is always a key sequence, because it does not depend on any prefix keys for its well-formedness.
At any time, several primary keymaps are active---that is, in use for finding key bindings. These are the global map, which is shared by all buffers; the local keymap, which is usually associated with a specific major mode; and zero or more minor mode keymaps, which belong to currently enabled minor modes. (Not all minor modes have keymaps.) The local keymap bindings shadow (i.e., take precedence over) the corresponding global bindings. The minor mode keymaps shadow both local and global keymaps. See section Active Keymaps, for details.
A keymap is a list whose CAR is the symbol keymap. The
remaining elements of the list define the key bindings of the keymap.
Use the function keymapp (see below) to test whether an object is
a keymap.
Several kinds of elements may appear in a keymap, after the symbol
keymap that begins it:
(type . binding)
(t . binding)
vector
nil for that
character. Such a binding of nil overrides any default key
binding in the keymap, for ASCII characters. However, default
bindings are still meaningful for events other than ASCII
characters. A binding of nil does not override
lower-precedence keymaps; thus, if the local map gives a binding of
nil, Emacs uses the binding from the global map.
string
Keymaps do not directly record bindings for the meta characters.
Instead, meta characters are regarded for
purposes of key lookup as sequences of two characters, the first of
which is ESC (or whatever is currently the value of
meta-prefix-char). Thus, the key M-a is really represented
as ESC a, and its global binding is found at the slot for
a in esc-map (see section Prefix Keys).
Here as an example is the local keymap for Lisp mode, a sparse keymap. It defines bindings for DEL and TAB, plus C-c C-l, M-C-q, and M-C-x.
lisp-mode-map
=>
(keymap
;; TAB
(9 . lisp-indent-line)
;; DEL
(127 . backward-delete-char-untabify)
(3 keymap
;; C-c C-l
(12 . run-lisp))
(27 keymap
;; M-C-q, treated as ESC C-q
(17 . indent-sexp)
;; M-C-x, treated as ESC C-x
(24 . lisp-send-defun)))
t if object is a keymap, nil
otherwise. More precisely, this function tests for a list whose
CAR is keymap.
(keymapp '(keymap))
=> t
(keymapp (current-global-map))
=> t
Here we describe the functions for creating keymaps.
nil, and does not bind any other kind of event.
(make-keymap)
=> (keymap [nil nil nil ... nil nil])
If you specify prompt, that becomes the overall prompt string for the keymap. The prompt string is useful for menu keymaps (see section Menu Keymaps).
make-keymap.
(make-sparse-keymap)
=> (keymap)
(setq map (copy-keymap (current-local-map)))
=> (keymap
;; (This implements meta characters.)
(27 keymap
(83 . center-paragraph)
(115 . center-line))
(9 . tab-to-tab-stop))
(eq map (current-local-map))
=> nil
(equal map (current-local-map))
=> t
A keymap can inherit the bindings of another keymap, which we call the parent keymap. Such a keymap looks like this:
(keymap bindings... . parent-keymap)
The effect is that this keymap inherits all the bindings of parent-keymap, whatever they may be at the time a key is looked up, but can add to them or override them with bindings.
If you change the bindings in parent-keymap using define-key
or other key-binding functions, these changes are visible in the
inheriting keymap unless shadowed by bindings. The converse is
not true: if you use define-key to change the inheriting keymap,
that affects bindings, but has no effect on parent-keymap.
The proper way to construct a keymap with a parent is to use
set-keymap-parent; if you have code that directly constructs a
keymap with a parent, please convert the program to use
set-keymap-parent instead.
keymap-parent returns nil.
nil, this function gives
keymap no parent at all.
If keymap has submaps (bindings for prefix keys), they too receive new parent keymaps that reflect what parent specifies for those prefix keys.
Here is an example showing how to make a keymap that inherits
from text-mode-map:
(let ((map (make-sparse-keymap))) (set-keymap-parent map text-mode-map) map)
A prefix key is a key sequence whose binding is a keymap. The
keymap defines what to do with key sequences that extend the prefix key.
For example, C-x is a prefix key, and it uses a keymap that is
also stored in the variable ctl-x-map. This keymap defines
bindings for key sequences starting with C-x.
Some of the standard Emacs prefix keys use keymaps that are also found in Lisp variables:
esc-map is the global keymap for the ESC prefix key. Thus,
the global definitions of all meta characters are actually found here.
This map is also the function definition of ESC-prefix.
help-map is the global keymap for the C-h prefix key.
mode-specific-map is the global keymap for the prefix key
C-c. This map is actually global, not mode-specific, but its name
provides useful information about C-c in the output of C-h b
(display-bindings), since the main use of this prefix key is for
mode-specific bindings.
ctl-x-map is the global keymap used for the C-x prefix key.
This map is found via the function cell of the symbol
Control-X-prefix.
mule-keymap is the global keymap used for the C-x RET
prefix key.
ctl-x-4-map is the global keymap used for the C-x 4 prefix
key.
ctl-x-5-map is the global keymap used for the C-x 5 prefix
key.
2C-mode-map is the global keymap used for the C-x 6 prefix
key.
vc-prefix-map is the global keymap used for the C-x v prefix
key.
facemenu-keymap is the global keymap used for the M-g
prefix key.
The keymap binding of a prefix key is used for looking up the event
that follows the prefix key. (It may instead be a symbol whose function
definition is a keymap. The effect is the same, but the symbol serves
as a name for the prefix key.) Thus, the binding of C-x is the
symbol Control-X-prefix, whose function cell holds the keymap
for C-x commands. (The same keymap is also the value of
ctl-x-map.)
Prefix key definitions can appear in any active keymap. The definitions of C-c, C-x, C-h and ESC as prefix keys appear in the global map, so these prefix keys are always available. Major and minor modes can redefine a key as a prefix by putting a prefix key definition for it in the local map or the minor mode's map. See section Active Keymaps.
If a key is defined as a prefix in more than one active map, then its various definitions are in effect merged: the commands defined in the minor mode keymaps come first, followed by those in the local map's prefix definition, and then by those from the global map.
In the following example, we make C-p a prefix key in the local
keymap, in such a way that C-p is identical to C-x. Then
the binding for C-p C-f is the function find-file, just
like C-x C-f. The key sequence C-p 6 is not found in any
active keymap.
(use-local-map (make-sparse-keymap))
=> nil
(local-set-key "\C-p" ctl-x-map)
=> nil
(key-binding "\C-p\C-f")
=> find-file
(key-binding "\C-p6")
=> nil
This function also sets symbol as a variable, with the keymap as its value. It returns symbol.
Emacs normally contains many keymaps; at any given time, just a few of them are active in that they participate in the interpretation of user input. These are the global keymap, the current buffer's local keymap, and the keymaps of any enabled minor modes.
The global keymap holds the bindings of keys that are defined
regardless of the current buffer, such as C-f. The variable
global-map holds this keymap, which is always active.
Each buffer may have another keymap, its local keymap, which may
contain new or overriding definitions for keys. The current buffer's
local keymap is always active except when overriding-local-map
overrides it. Text properties can specify an alternative local map for
certain parts of the buffer; see section Properties with Special Meanings.
Each minor mode can have a keymap; if it does, the keymap is active when the minor mode is enabled.
The variable overriding-local-map, if non-nil, specifies
another local keymap that overrides the buffer's local map and all the
minor mode keymaps.
All the active keymaps are used together to determine what command to execute when a key is entered. Emacs searches these maps one by one, in order of decreasing precedence, until it finds a binding in one of the maps. The procedure for searching a single keymap is called key lookup; see section Key Lookup.
Normally, Emacs first searches for the key in the minor mode maps, in
the order specified by minor-mode-map-alist; if they do not
supply a binding for the key, Emacs searches the local map; if that too
has no binding, Emacs then searches the global map. However, if
overriding-local-map is non-nil, Emacs searches that map
first, before the global map.
Since every buffer that uses the same major mode normally uses the
same local keymap, you can think of the keymap as local to the mode. A
change to the local keymap of a buffer (using local-set-key, for
example) is seen also in the other buffers that share that keymap.
The local keymaps that are used for Lisp mode and some other major
modes exist even if they have not yet been used. These local maps are
the values of variables such as lisp-mode-map. For most major
modes, which are less frequently used, the local keymap is constructed
only when the mode is used for the first time in a session.
The minibuffer has local keymaps, too; they contain various completion and exit commands. See section Introduction to Minibuffers.
Emacs has other keymaps that are used in a different way--translating
events within read-key-sequence. See section Translating Input Events.
See section Standard Keymaps, for a list of standard keymaps.
self-insert-command to all of the printing characters.
It is normal practice to change the bindings in the global map, but you should not assign this variable any value other than the keymap it starts out with.
global-map unless you change one or the
other.
(current-global-map)
=> (keymap [set-mark-command beginning-of-line ...
delete-backward-char])
nil
if it has none. In the following example, the keymap for the
`*scratch*' buffer (using Lisp Interaction mode) is a sparse keymap
in which the entry for ESC, ASCII code 27, is another sparse
keymap.
(current-local-map)
=> (keymap
(10 . eval-print-last-sexp)
(9 . lisp-indent-line)
(127 . backward-delete-char-untabify)
(27 keymap
(24 . eval-defun)
(17 . indent-sexp)))
nil.
It is very unusual to change the global keymap.
nil, then the buffer has no local
keymap. use-local-map returns nil. Most major mode
commands use this function.
(variable . keymap)
The keymap keymap is active whenever variable has a
non-nil value. Typically variable is the variable that
enables or disables a minor mode. See section Keymaps and Minor Modes.
Note that elements of minor-mode-map-alist do not have the same
structure as elements of minor-mode-alist. The map must be the
CDR of the element; a list with the map as the CADR will not
do. The CADR can be either a keymap (a list) or a symbol
whose function definition is a keymap.
When more than one minor mode keymap is active, their order of priority
is the order of minor-mode-map-alist. But you should design
minor modes so that they don't interfere with each other. If you do
this properly, the order will not matter.
See section Keymaps and Minor Modes, for more information about minor
modes. See also minor-mode-key-binding (see section Functions for Key Lookup).
minor-mode-map-alist: (variable
. keymap).
If a variable appears as an element of
minor-mode-overriding-map-alist, the map specified by that
element totally replaces any map specified for the same variable in
minor-mode-map-alist.
minor-mode-overriding-map-alist is automatically buffer-local in
all buffers.
nil, this variable holds a keymap to use instead of the
buffer's local keymap and instead of all the minor mode keymaps. This
keymap, if any, overrides all other maps that would have been active,
except for the current global map.
nil, this variable holds a keymap to use instead of
overriding-local-map, the buffer's local keymap and all the minor
mode keymaps.
This variable is always local to the current terminal and cannot be buffer-local. See section Multiple Displays. It is used to implement incremental search mode.
nil, the value of
overriding-local-map or overriding-terminal-local-map can
affect the display of the menu bar. The default value is nil, so
those map variables have no effect on the menu bar.
Note that these two map variables do affect the execution of key sequences entered using the menu bar, even if they do not affect the menu bar display. So if a menu bar key sequence comes in, you should clear the variables before looking up and executing that key sequence. Modes that use the variables would typically do this anyway; normally they respond to events that they do not handle by "unreading" them and exiting.
read-event. See section Special Events.
Key lookup is the process of finding the binding of a key sequence from a given keymap. Actual execution of the binding is not part of key lookup.
Key lookup uses just the event type of each event in the key sequence;
the rest of the event is ignored. In fact, a key sequence used for key
lookup may designate mouse events with just their types (symbols)
instead of with entire mouse events (lists). See section Input Events. Such
a "key-sequence" is insufficient for command-execute to run,
but it is sufficient for looking up or rebinding a key.
When the key sequence consists of multiple events, key lookup processes the events sequentially: the binding of the first event is found, and must be a keymap; then the second event's binding is found in that keymap, and so on until all the events in the key sequence are used up. (The binding thus found for the last event may or may not be a keymap.) Thus, the process of key lookup is defined in terms of a simpler process for looking up a single event in a keymap. How that is done depends on the type of object associated with the event in that keymap.
Let's use the term keymap entry to describe the value found by
looking up an event type in a keymap. (This doesn't include the item
string and other extra elements in menu key bindings, because
lookup-key and other key lookup functions don't include them in
the returned value.) While any Lisp object may be stored in a keymap as
a keymap entry, not all make sense for key lookup. Here is a table of
the meaningful kinds of keymap entries:
nil
nil means that the events used so far in the lookup form an
undefined key. When a keymap fails to mention an event type at all, and
has no default binding, that is equivalent to a binding of nil
for that event type.
keymap, then the list
is a keymap, and is treated as a keymap (see above).
lambda, then the list is a
lambda expression. This is presumed to be a command, and is treated as
such (see above).
(othermap . othertype)When key lookup encounters an indirect entry, it looks up instead the binding of othertype in othermap and uses that. This feature permits you to define one key as an alias for another key. For example, an entry whose CAR is the keymap called
esc-map
and whose CDR is 32 (the code for SPC) means, "Use the global
binding of Meta-SPC, whatever that may be."
command-execute
(see section Interactive Call).
The symbol undefined is worth special mention: it means to treat
the key as undefined. Strictly speaking, the key is defined, and its
binding is the command undefined; but that command does the same
thing that is done automatically for an undefined key: it rings the bell
(by calling ding) but does not signal an error.
undefined is used in local keymaps to override a global key
binding and make the key "undefined" locally. A local binding of
nil would fail to do this because it would not override the
global binding.
In short, a keymap entry may be a keymap, a command, a keyboard macro,
a symbol that leads to one of them, or an indirection or nil.
Here is an example of a sparse keymap with two characters bound to
commands and one bound to another keymap. This map is the normal value
of emacs-lisp-mode-map. Note that 9 is the code for TAB,
127 for DEL, 27 for ESC, 17 for C-q and 24 for
C-x.
(keymap (9 . lisp-indent-line)
(127 . backward-delete-char-untabify)
(27 keymap (17 . indent-sexp) (24 . eval-defun)))
Here are the functions and variables pertaining to key lookup.
lookup-key. Here are examples:
(lookup-key (current-global-map) "\C-x\C-f")
=> find-file
(lookup-key (current-global-map) "\C-x\C-f12345")
=> 2
If the string or vector key is not a valid key sequence according to the prefix keys specified in keymap, it must be "too long" and have extra events at the end that do not fit into a single key sequence. Then the value is a number, the number of events at the front of key that compose a complete key.
If accept-defaults is non-nil, then lookup-key
considers default bindings as well as bindings for the specific events
in key. Otherwise, lookup-key reports only bindings for
the specific sequence key, ignoring default bindings except when
you explicitly ask about them. (To do this, supply t as an
element of key; see section Format of Keymaps.)
If key contains a meta character, that character is implicitly
replaced by a two-character sequence: the value of
meta-prefix-char, followed by the corresponding non-meta
character. Thus, the first example below is handled by conversion into
the second example.
(lookup-key (current-global-map) "\M-f")
=> forward-word
(lookup-key (current-global-map) "\ef")
=> forward-word
Unlike read-key-sequence, this function does not modify the
specified events in ways that discard information (see section Key Sequence Input). In particular, it does not convert letters to lower case and
it does not change drag events to clicks.
ding, but does
not cause an error.
nil if
key is undefined in the keymaps.
The argument accept-defaults controls checking for default
bindings, as in lookup-key (above).
An error is signaled if key is not a string or a vector.
(key-binding "\C-x\C-f")
=> find-file
nil if it is undefined there.
The argument accept-defaults controls checking for default bindings,
as in lookup-key (above).
nil if it is undefined there.
The argument accept-defaults controls checking for default bindings,
as in lookup-key (above).
(modename . binding), where modename is the
variable that enables the minor mode, and binding is key's
binding in that mode. If key has no minor-mode bindings, the
value is nil.
If the first binding found is not a prefix definition (a keymap or a symbol defined as a keymap), all subsequent bindings from other minor modes are omitted, since they would be completely shadowed. Similarly, the list omits non-prefix bindings that follow prefix bindings.
The argument accept-defaults controls checking for default
bindings, as in lookup-key (above).
As long as the value of meta-prefix-char remains 27, key
lookup translates M-b into ESC b, which is normally
defined as the backward-word command. However, if you set
meta-prefix-char to 24, the code for C-x, then Emacs will
translate M-b into C-x b, whose standard binding is the
switch-to-buffer command. Here is an illustration:
meta-prefix-char ; The default value.
=> 27
(key-binding "\M-b")
=> backward-word
?\C-x ; The print representation
=> 24 ; of a character.
(setq meta-prefix-char 24)
=> 24
(key-binding "\M-b")
=> switch-to-buffer ; Now, typing M-b is
; like typing C-x b.
(setq meta-prefix-char 27) ; Avoid confusion!
=> 27 ; Restore the default value!
The way to rebind a key is to change its entry in a keymap. If you
change a binding in the global keymap, the change is effective in all
buffers (though it has no direct effect in buffers that shadow the
global binding with a local one). If you change the current buffer's
local map, that usually affects all buffers using the same major mode.
The global-set-key and local-set-key functions are
convenient interfaces for these operations (see section Commands for Binding Keys). You can also use define-key, a more general
function; then you must specify explicitly the map to change.
In writing the key sequence to rebind, it is good to use the special
escape sequences for control and meta characters (see section String Type).
The syntax `\C-' means that the following character is a control
character and `\M-' means that the following character is a meta
character. Thus, the string "\M-x" is read as containing a
single M-x, "\C-f" is read as containing a single
C-f, and "\M-\C-x" and "\C-\M-x" are both read as
containing a single C-M-x. You can also use this escape syntax in
vectors, as well as others that aren't allowed in strings; one example
is `[?\C-\H-x home]'. See section Character Type.
The key definition and lookup functions accept an alternate syntax for
event types in a key sequence that is a vector: you can use a list
containing modifier names plus one base event (a character or function
key name). For example, (control ?a) is equivalent to
?\C-a and (hyper control left) is equivalent to
C-H-left. One advantage of such lists is that the precise
numeric codes for the modifier bits don't appear in compiled files.
For the functions below, an error is signaled if keymap is not a keymap or if key is not a string or vector representing a key sequence. You can use event types (symbols) as shorthand for events that are lists.
define-key is binding.
Every prefix of key must be a prefix key (i.e., bound to a keymap)
or undefined; otherwise an error is signaled. If some prefix of
key is undefined, then define-key defines it as a prefix
key so that the rest of key can be defined as specified.
If there was previously no binding for key in keymap, the new binding is added at the beginning of keymap. The order of bindings in a keymap makes no difference in most cases, but it does matter for menu keymaps (see section Menu Keymaps).
Here is an example that creates a sparse keymap and makes a number of bindings in it:
(setq map (make-sparse-keymap))
=> (keymap)
(define-key map "\C-f" 'forward-char)
=> forward-char
map
=> (keymap (6 . forward-char))
;; Build sparse submap for C-x and bind f in that.
(define-key map "\C-xf" 'forward-word)
=> forward-word
map
=> (keymap
(24 keymap ; C-x
(102 . forward-word)) ; f
(6 . forward-char)) ; C-f
;; Bind C-p to the ctl-x-map.
(define-key map "\C-p" ctl-x-map)
;; ctl-x-map
=> [nil ... find-file ... backward-kill-sentence]
;; Bind C-f to foo in the ctl-x-map.
(define-key map "\C-p\C-f" 'foo)
=> 'foo
map
=> (keymap ; Note foo in ctl-x-map.
(16 keymap [nil ... foo ... backward-kill-sentence])
(24 keymap
(102 . forward-word))
(6 . forward-char))
Note that storing a new binding for C-p C-f actually works by
changing an entry in ctl-x-map, and this has the effect of
changing the bindings of both C-p C-f and C-x C-f in the
default global map.
nil.
For example, this redefines C-x C-f, if you do it in an Emacs with standard bindings:
(substitute-key-definition 'find-file 'find-file-read-only (current-global-map))
If oldmap is non-nil, then its bindings determine which
keys to rebind. The rebindings still happen in keymap, not in
oldmap. Thus, you can change one map under the control of the
bindings in another. For example,
(substitute-key-definition 'delete-backward-char 'my-funny-delete my-map global-map)
puts the special deletion command in my-map for whichever keys
are globally bound to the standard deletion command.
Here is an example showing a keymap before and after substitution:
(setq map '(keymap
(?1 . olddef-1)
(?2 . olddef-2)
(?3 . olddef-1)))
=> (keymap (49 . olddef-1) (50 . olddef-2) (51 . olddef-1))
(substitute-key-definition 'olddef-1 'newdef map)
=> nil
map
=> (keymap (49 . newdef) (50 . olddef-2) (51 . newdef))
undefined. This makes ordinary insertion of
text impossible. suppress-keymap returns nil.
If nodigits is nil, then suppress-keymap defines
digits to run digit-argument, and - to run
negative-argument. Otherwise it makes them undefined like the
rest of the printing characters.
The suppress-keymap function does not make it impossible to
modify a buffer, as it does not suppress commands such as yank
and quoted-insert. To prevent any modification of a buffer, make
it read-only (see section Read-Only Buffers).
Since this function modifies keymap, you would normally use it
on a newly created keymap. Operating on an existing keymap
that is used for some other purpose is likely to cause trouble; for
example, suppressing global-map would make it impossible to use
most of Emacs.
Most often, suppress-keymap is used to initialize local
keymaps of modes such as Rmail and Dired where insertion of text is not
desirable and the buffer is read-only. Here is an example taken from
the file `emacs/lisp/dired.el', showing how the local keymap for
Dired mode is set up:
(setq dired-mode-map (make-keymap)) (suppress-keymap dired-mode-map) (define-key dired-mode-map "r" 'dired-rename-file) (define-key dired-mode-map "\C-d" 'dired-flag-file-deleted) (define-key dired-mode-map "d" 'dired-flag-file-deleted) (define-key dired-mode-map "v" 'dired-view-file) (define-key dired-mode-map "e" 'dired-find-file) (define-key dired-mode-map "f" 'dired-find-file) ...
This section describes some convenient interactive interfaces for
changing key bindings. They work by calling define-key.
People often use global-set-key in their `.emacs' file for
simple customization. For example,
(global-set-key "\C-x\C-\\" 'next-line)
or
(global-set-key [?\C-x ?\C-\\] 'next-line)
or
(global-set-key [(control ?x) (control ?\\)] 'next-line)
redefines C-x C-\ to move down a line.
(global-set-key [M-mouse-1] 'mouse-set-point)
redefines the first (leftmost) mouse button, typed with the Meta key, to set point where you click.
(global-set-key key definition) == (define-key (current-global-map) key definition)
One use of this function is in preparation for defining a longer key that uses key as a prefix--which would not be allowed if key has a non-prefix binding. For example:
(global-unset-key "\C-l")
=> nil
(global-set-key "\C-l\C-l" 'redraw-display)
=> nil
This function is implemented simply using define-key:
(global-unset-key key) == (define-key (current-global-map) key nil)
(local-set-key key definition) == (define-key (current-local-map) key definition)
(local-unset-key key) == (define-key (current-local-map) key nil)
This section describes functions used to scan all the current keymaps for the sake of printing help information.
(key .
map), where key is a prefix key whose definition in
keymap is map.
The elements of the alist are ordered so that the key increases
in length. The first element is always ("" . keymap),
because the specified keymap is accessible from itself with a prefix of
no events.
If prefix is given, it should be a prefix key sequence; then
accessible-keymaps includes only the submaps whose prefixes start
with prefix. These elements look just as they do in the value of
(accessible-keymaps); the only difference is that some elements
are omitted.
In the example below, the returned alist indicates that the key
ESC, which is displayed as `^[', is a prefix key whose
definition is the sparse keymap (keymap (83 . center-paragraph)
(115 . foo)).
(accessible-keymaps (current-local-map))
=>(("" keymap
(27 keymap ; Note this keymap for ESC is repeated below.
(83 . center-paragraph)
(115 . center-line))
(9 . tab-to-tab-stop))
("^[" keymap
(83 . center-paragraph)
(115 . foo)))
In the following example, C-h is a prefix key that uses a sparse
keymap starting with (keymap (118 . describe-variable)...).
Another prefix, C-x 4, uses a keymap which is also the value of
the variable ctl-x-4-map. The event mode-line is one of
several dummy events used as prefixes for mouse actions in special parts
of a window.
(accessible-keymaps (current-global-map))
=> (("" keymap [set-mark-command beginning-of-line ...
delete-backward-char])
("^H" keymap (118 . describe-variable) ...
(8 . help-for-help))
("^X" keymap [x-flush-mouse-queue ...
backward-kill-sentence])
("^[" keymap [mark-sexp backward-sexp ...
backward-kill-word])
("^X4" keymap (15 . display-buffer) ...)
([mode-line] keymap
(S-mouse-2 . mouse-split-window-horizontally) ...))
These are not all the keymaps you would see in actuality.
where-is command
(see section `Help' in The GNU Emacs Manual). It returns a list
of key sequences (of any length) that are bound to command in a
set of keymaps.
The argument command can be any object; it is compared with all
keymap entries using eq.
If keymap is nil, then the maps used are the current active
keymaps, disregarding overriding-local-map (that is, pretending
its value is nil). If keymap is non-nil, then the
maps searched are keymap and the global keymap.
Usually it's best to use overriding-local-map as the expression
for keymap. Then where-is-internal searches precisely the
keymaps that are active. To search only the global map, pass
(keymap) (an empty keymap) as keymap.
If firstonly is non-ascii, then the value is a single
string representing the first key sequence found, rather than a list of
all possible key sequences. If firstonly is t, then the
value is the first key sequence, except that key sequences consisting
entirely of ASCII characters (or meta variants of ASCII
characters) are preferred to all other key sequences.
If noindirect is non-nil, where-is-internal doesn't
follow indirect keymap bindings. This makes it possible to search for
an indirect definition itself.
(where-is-internal 'describe-function)
=> ("\^hf" "\^hd")
If prefix is non-nil, it should be a prefix key; then the
listing includes only keys that start with prefix.
The listing describes meta characters as ESC followed by the corresponding non-meta character.
When several characters with consecutive ASCII codes have the
same definition, they are shown together, as
`firstchar..lastchar'. In this instance, you need to
know the ASCII codes to understand which characters this means.
For example, in the default global map, the characters `SPC
.. ~' are described by a single line. SPC is ASCII 32,
~ is ASCII 126, and the characters between them include all
the normal printing characters, (e.g., letters, digits, punctuation,
etc.); all these characters are bound to self-insert-command.
A keymap can define a menu as well as bindings for keyboard keys and mouse button. Menus are usually actuated with the mouse, but they can work with the keyboard also.
A keymap is suitable for menu use if it has an overall prompt
string, which is a string that appears as an element of the keymap.
(See section Format of Keymaps.) The string should describe the purpose of
the menu. The easiest way to construct a keymap with a prompt string is
to specify the string as an argument when you call make-keymap or
make-sparse-keymap (see section Creating Keymaps).
The order of items in the menu is the same as the order of bindings in
the keymap. Since define-key puts new bindings at the front, you
should define the menu items starting at the bottom of the menu and
moving to the top, if you care about the order. When you add an item to
an existing menu, you can specify its position in the menu using
define-key-after (see section Modifying Menus).
The simpler and older way to define a menu keymap binding looks like this:
(item-string . real-binding)
The CAR, item-string, is the string to be displayed in the menu. It should be short--preferably one to three words. It should describe the action of the command it corresponds to.
You can also supply a second string, called the help string, as follows:
(item-string help-string . real-binding)
Currently Emacs does not actually use help-string; it knows only how to ignore help-string in order to extract real-binding. In the future we may use help-string as extended documentation for the menu item, available on request.
As far as define-key is concerned, item-string and
help-string are part of the event's binding. However,
lookup-key returns just real-binding, and only
real-binding is used for executing the key.
If real-binding is nil, then item-string appears in
the menu but cannot be selected.
If real-binding is a symbol and has a non-nil
menu-enable property, that property is an expression that
controls whether the menu item is enabled. Every time the keymap is
used to display a menu, Emacs evaluates the expression, and it enables
the menu item only if the expression's value is non-nil. When a
menu item is disabled, it is displayed in a "fuzzy" fashion, and
cannot be selected.
The menu bar does not recalculate which items are enabled every time you
look at a menu. This is because the X toolkit requires the whole tree
of menus in advance. To force recalculation of the menu bar, call
force-mode-line-update (see section Mode Line Format).
You've probably noticed that menu items show the equivalent keyboard key sequence (if any) to invoke the same command. To save time on recalculation, menu display caches this information in a sublist in the binding, like this:
(item-string [help-string] (key-binding-data) . real-binding)
Don't put these sublists in the menu item yourself; menu display calculates them automatically. Don't mention keyboard equivalents in the item strings themselves, since that is redundant.
An extended-format menu item is a more flexible and also cleaner
alternative to the simple format. It consists of a list that starts
with the symbol menu-item. To define a non-selectable string,
the item looks like this:
(menu-item item-name)
where a string consisting of two or more dashes specifies a separator line.
To define a real menu item which can be selected, the extended format item looks like this:
(menu-item item-name real-binding
. item-property-list)
Here, item-name is an expression which evaluates to the menu item string. Thus, the string need not be a constant. The third element, real-binding, is the command to execute. The tail of the list, item-property-list, has the form of a property list which contains other information. Here is a table of the properties that are supported:
:enable FORM
nil means yes).
:visible FORM
nil means yes). If the item
does not appear, then the menu is displayed as if this item were
not defined at all.
:help help
:button (type . selected)
:toggle or
:radio. The CDR, selected, should be a form; the
result of evaluating it says whether this button is currently selected.
A toggle is a menu item which is labeled as either "on" or "off"
according to the value of selected. The command itself should
toggle selected, setting it to t if it is nil,
and to nil if it is t. Here is how the menu item
to toggle the debug-on-error flag is defined:
(menu-item "Debug on Error" toggle-debug-on-error
:button (:toggle
. (and (boundp 'debug-on-error)
debug-on-error))
This works because toggle-debug-on-error is defined as a command
which toggles the variable debug-on-error.
Radio buttons are a group of menu items, in which at any time one
and only one is "selected." There should be a variable whose value
says which one is selected at any time. The selected form for
each radio button in the group should check whether the variable has the
right value for selecting that button. Clicking on the button should
set the variable so that the button you clicked on becomes selected.
:key-sequence key-sequence
:key-sequence nil
:keys property and finds the keyboard
equivalent anyway.
:keys string
:filter filter-fn
Sometimes it is useful to make menu items that use the "same"
command but with different enable conditions. The best way to do this
in Emacs now is with extended menu items; before that feature existed,
it could be done by defining alias commands and using them in menu
items. Here's an example that makes two aliases for
toggle-read-only and gives them different enable conditions:
(defalias 'make-read-only 'toggle-read-only) (put 'make-read-only 'menu-enable '(not buffer-read-only)) (defalias 'make-writable 'toggle-read-only) (put 'make-writable 'menu-enable 'buffer-read-only)
When using aliases in menus, often it is useful to display the
equivalent key bindings for the "real" command name, not the aliases
(which typically don't have any key bindings except for the menu
itself). To request this, give the alias symbol a non-nil
menu-alias property. Thus,
(put 'make-read-only 'menu-alias t) (put 'make-writable 'menu-alias t)
causes menu items for make-read-only and make-writable to
show the keyboard bindings for toggle-read-only.
The usual way to make a menu keymap produce a menu is to make it the definition of a prefix key. (A Lisp program can explicitly pop up a menu and receive the user's choice--see section Pop-Up Menus.)
If the prefix key ends with a mouse event, Emacs handles the menu keymap by popping up a visible menu, so that the user can select a choice with the mouse. When the user clicks on a menu item, the event generated is whatever character or symbol has the binding that brought about that menu item. (A menu item may generate a series of events if the menu has multiple levels or comes from the menu bar.)
It's often best to use a button-down event to trigger the menu. Then the user can select a menu item by releasing the button.
A single keymap can appear as multiple menu panes, if you explicitly arrange for this. The way to do this is to make a keymap for each pane, then create a binding for each of those maps in the main keymap of the menu. Give each of these bindings an item string that starts with `@'. The rest of the item string becomes the name of the pane. See the file `lisp/mouse.el' for an example of this. Any ordinary bindings with `@'-less item strings are grouped into one pane, which appears along with the other panes explicitly created for the submaps.
X toolkit menus don't have panes; instead, they can have submenus. Every nested keymap becomes a submenu, whether the item string starts with `@' or not. In a toolkit version of Emacs, the only thing special about `@' at the beginning of an item string is that the `@' doesn't appear in the menu item.
You can also produce multiple panes or submenus from separate keymaps. The full definition of a prefix key always comes from merging the definitions supplied by the various active keymaps (minor mode, local, and global). When more than one of these keymaps is a menu, each of them makes a separate pane or panes (when Emacs does not use an X-toolkit) or a separate submenu (when using an X-toolkit). See section Active Keymaps.
When a prefix key ending with a keyboard event (a character or function key) has a definition that is a menu keymap, the user can use the keyboard to choose a menu item.
Emacs displays the menu alternatives (the item strings of the bindings)
in the echo area. If they don't all fit at once, the user can type
SPC to see the next line of alternatives. Successive uses of
SPC eventually get to the end of the menu and then cycle around to
the beginning. (The variable menu-prompt-more-char specifies
which character is used for this; SPC is the default.)
When the user has found the desired alternative from the menu, he or she should type the corresponding character--the one whose binding is that alternative.
This way of using menus in an Emacs-like editor was inspired by the Hierarkey system.
Here is a complete example of defining a menu keymap. It is the definition of the `Print' submenu in the `Tools' menu in the menu bar, and it uses the simple menu item format (see section Simple Menu Items). First we create the keymap, and give it a name:
(defvar menu-bar-print-menu (make-sparse-keymap "Print"))
Next we define the menu items:
(define-key menu-bar-print-menu [ps-print-region]
'("Postscript Print Region" . ps-print-region-with-faces))
(define-key menu-bar-print-menu [ps-print-buffer]
'("Postscript Print Buffer" . ps-print-buffer-with-faces))
(define-key menu-bar-print-menu [separator-ps-print]
'("--"))
(define-key menu-bar-print-menu [print-region]
'("Print Region" . print-region))
(define-key menu-bar-print-menu [print-buffer]
'("Print Buffer" . print-buffer))
Note the symbols which the bindings are "made for"; these appear
inside square brackets, in the key sequence being defined. In some
cases, this symbol is the same as the command name; sometimes it is
different. These symbols are treated as "function keys", but they are
not real function keys on the keyboard. They do not affect the
functioning of the menu itself, but they are "echoed" in the echo area
when the user selects from the menu, and they appear in the output of
where-is and apropos.
The binding whose definition is ("--") is a separator line.
Like a real menu item, the separator has a key symbol, in this case
separator-ps-print. If one menu has two separators, they must
have two different key symbols.
Here is code to define enable conditions for two of the commands in the menu:
(put 'print-region 'menu-enable 'mark-active) (put 'ps-print-region-with-faces 'menu-enable 'mark-active)
Here is how we make this menu appear as an item in the parent menu:
(define-key menu-bar-tools-menu [print] (cons "Print" menu-bar-print-menu))
Note that this incorporates the submenu keymap, which is the value of
the variable menu-bar-print-menu, rather than the symbol
menu-bar-print-menu itself. Using that symbol in the parent menu
item would be meaningless because menu-bar-print-menu is not a
command.
If you wanted to attach the same print menu to a mouse click, you can do it this way:
(define-key global-map [C-S-down-mouse-1] menu-bar-print-menu)
We could equally well use an extended menu item (see section Extended Menu Items) for print-region, like this:
(define-key menu-bar-print-menu [print-region]
'(menu-item "Print Region" print-region
:enable (mark-active)))
With the extended menu item, the enable condition is specified inside the menu item itself. If we wanted to make this item disappear from the menu entirely when the mark is inactive, we could do it this way:
(define-key menu-bar-print-menu [print-region]
'(menu-item "Print Region" print-region
:visible (mark-active)))
Most window systems allow each frame to have a menu bar---a
permanently displayed menu stretching horizontally across the top of the
frame. The items of the menu bar are the subcommands of the fake
"function key" menu-bar, as defined by all the active keymaps.
To add an item to the menu bar, invent a fake "function key" of your
own (let's call it key), and make a binding for the key sequence
[menu-bar key]. Most often, the binding is a menu keymap,
so that pressing a button on the menu bar item leads to another menu.
When more than one active keymap defines the same fake function key for the menu bar, the item appears just once. If the user clicks on that menu bar item, it brings up a single, combined menu containing all the subcommands of that item--the global subcommands, the local subcommands, and the minor mode subcommands.
The variable overriding-local-map is normally ignored when
determining the menu bar contents. That is, the menu bar is computed
from the keymaps that would be active if overriding-local-map
were nil. See section Active Keymaps.
In order for a frame to display a menu bar, its menu-bar-lines
parameter must be greater than zero. Emacs uses just one line for the
menu bar itself; if you specify more than one line, the other lines
serve to separate the menu bar from the windows in the frame. We
recommend 1 or 2 as the value of menu-bar-lines. See section Window Frame Parameters.
Here's an example of setting up a menu bar item:
(modify-frame-parameters (selected-frame)
'((menu-bar-lines . 2)))
;; Make a menu keymap (with a prompt string)
;; and make it the menu bar item's definition.
(define-key global-map [menu-bar words]
(cons "Words" (make-sparse-keymap "Words")))
;; Define specific subcommands in this menu.
(define-key global-map
[menu-bar words forward]
'("Forward word" . forward-word))
(define-key global-map
[menu-bar words backward]
'("Backward word" . backward-word))
A local keymap can cancel a menu bar item made by the global keymap by
rebinding the same fake function key with undefined as the
binding. For example, this is how Dired suppresses the `Edit' menu
bar item:
(define-key dired-mode-map [menu-bar edit] 'undefined)
edit is the fake function key used by the global map for the
`Edit' menu bar item. The main reason to suppress a global
menu bar item is to regain space for mode-specific items.
This variable holds a list of fake function keys for items to display at
the end of the menu bar rather than in normal sequence. The default
value is (help-menu); thus, the `Help' menu item normally appears
at the end of the menu bar, following local menu items.
When you insert a new item in an existing menu, you probably want to
put it in a particular place among the menu's existing items. If you
use define-key to add the item, it normally goes at the front of
the menu. To put it elsewhere in the menu, use define-key-after:
define-key, but position the binding in map after
the binding for the event after. The argument key should be
of length one--a vector or string with just one element. But
after should be a single event type--a symbol or a character, not
a sequence. The new binding goes after the binding for after. If
after is t, then the new binding goes last, at the end of
the keymap.
Here is an example:
(define-key-after my-menu [drink]
'("Drink" . drink-command) 'eat)
makes a binding for the fake function key DRINK and puts it right after the binding for EAT.
Here is how to insert an item called `Work' in the `Signals'
menu of Shell mode, after the item break:
(define-key-after
(lookup-key shell-mode-map [menu-bar signals])
[work] '("Work" . work-command) 'break)
A mode is a set of definitions that customize Emacs and can be turned on and off while you edit. There are two varieties of modes: major modes, which are mutually exclusive and used for editing particular kinds of text, and minor modes, which provide features that users can enable individually.
This chapter describes how to write both major and minor modes, how to indicate them in the mode line, and how they run hooks supplied by the user. For related topics such as keymaps and syntax tables, see section Keymaps, and section Syntax Tables.
Major modes specialize Emacs for editing particular kinds of text. Each buffer has only one major mode at a time.
The least specialized major mode is called Fundamental mode.
This mode has no mode-specific definitions or variable settings, so each
Emacs command behaves in its default manner, and each option is in its
default state. All other major modes redefine various keys and options.
For example, Lisp Interaction mode provides special key bindings for
C-j (eval-print-last-sexp), TAB
(lisp-indent-line), and other keys.
When you need to write several editing commands to help you perform a specialized editing task, creating a new major mode is usually a good idea. In practice, writing a major mode is easy (in contrast to writing a minor mode, which is often difficult).
If the new mode is similar to an old one, it is often unwise to modify the old one to serve two purposes, since it may become harder to use and maintain. Instead, copy and rename an existing major mode definition and alter the copy--or define a derived mode (see section Defining Derived Modes). For example, Rmail Edit mode, which is in `emacs/lisp/rmailedit.el', is a major mode that is very similar to Text mode except that it provides three additional commands. Its definition is distinct from that of Text mode, but was derived from it.
Rmail Edit mode offers an example of changing the major mode temporarily for a buffer, so it can be edited in a different way (with ordinary Emacs commands rather than Rmail commands). In such cases, the temporary major mode usually has a command to switch back to the buffer's usual mode (Rmail mode, in this case). You might be tempted to present the temporary redefinitions inside a recursive edit and restore the usual ones when the user exits; but this is a bad idea because it constrains the user's options when it is done in more than one buffer: recursive edits must be exited most-recently-entered first. Using an alternative major mode avoids this limitation. See section Recursive Editing.
The standard GNU Emacs Lisp library directory contains the code for several major modes, in files such as `text-mode.el', `texinfo.el', `lisp-mode.el', `c-mode.el', and `rmail.el'. You can study these libraries to see how modes are written. Text mode is perhaps the simplest major mode aside from Fundamental mode. Rmail mode is a complicated and specialized mode.
The code for existing major modes follows various coding conventions, including conventions for local keymap and syntax table initialization, global names, and hooks. Please follow these conventions when you define a new major mode:
describe-mode) in your mode will display this string.
The documentation string may include the special documentation
substrings, `\[command]', `\{keymap}', and
`\<keymap>', that enable the documentation to adapt
automatically to the user's own key bindings. See section Substituting Key Bindings in Documentation.
kill-all-local-variables. This is what gets rid of the
buffer-local variables of the major mode previously in effect.
major-mode to the
major mode command symbol. This is how describe-mode discovers
which documentation to print.
mode-name to the
"pretty" name of the mode, as a string. This string appears in the
mode line.
use-local-map to install this local map. See section Active Keymaps, for more information.
This keymap should be stored permanently in a global variable named
modename-mode-map. Normally the library that defines the
mode sets this variable.
See section Tips for Defining Variables Robustly, for advice about how to write the code to set
up the mode's keymap variable.
modename-mode-syntax-table. See section Syntax Tables.
modename-mode-abbrev-table. See section Abbrev Tables.
font-lock-defaults (see section Font Lock Mode).
imenu-generic-expression or
imenu-create-index-function (see section Imenu).
defvar or defcustom to set mode-related variables, so
that they are not reinitialized if they already have a value. (Such
reinitialization could discard customizations made by the user.)
make-local-variable in the major mode command, not
make-variable-buffer-local. The latter function would make the
variable local to every buffer in which it is subsequently set, which
would affect buffers that do not use this mode. It is undesirable for a
mode to have such global effects. See section Buffer-Local Variables.
It's OK to use make-variable-buffer-local, if you wish, for a
variable used only within a single Lisp package.
modename-mode-hook. The major mode command should run that
hook, with run-hooks, as the very last thing it
does. See section Hooks.
indented-text-mode runs text-mode-hook as
well as indented-text-mode-hook. It may run these other hooks
immediately before the mode's own hook (that is, after everything else),
or it may run them earlier.
change-major-mode-hook (see section Creating and Deleting Buffer-Local Bindings).
mode-class
with value special, put on as follows:
(put 'funny-mode 'mode-class 'special)This tells Emacs that new buffers created while the current buffer has Funny mode should not inherit Funny mode. Modes such as Dired, Rmail, and Buffer List use this feature.
auto-mode-alist to select
the mode for those file names. If you define the mode command to
autoload, you should add this element in the same file that calls
autoload. Otherwise, it is sufficient to add the element in the
file that contains the mode definition. See section How Emacs Chooses a Major Mode.
autoload form
and an example of how to add to auto-mode-alist, that users can
include in their `.emacs' files.
Text mode is perhaps the simplest mode besides Fundamental mode. Here are excerpts from `text-mode.el' that illustrate many of the conventions listed above:
;; Create mode-specific tables.
(defvar text-mode-syntax-table nil
"Syntax table used while in text mode.")
(if text-mode-syntax-table
() ; Do not change the table if it is already set up.
(setq text-mode-syntax-table (make-syntax-table))
(modify-syntax-entry ?\" ". " text-mode-syntax-table)
(modify-syntax-entry ?\\ ". " text-mode-syntax-table)
(modify-syntax-entry ?' "w " text-mode-syntax-table))
(defvar text-mode-abbrev-table nil
"Abbrev table used while in text mode.")
(define-abbrev-table 'text-mode-abbrev-table ())
(defvar text-mode-map nil) ; Create a mode-specific keymap.
(if text-mode-map
() ; Do not change the keymap if it is already set up.
(setq text-mode-map (make-sparse-keymap))
(define-key text-mode-map "\t" 'indent-relative)
(define-key text-mode-map "\es" 'center-line)
(define-key text-mode-map "\eS" 'center-paragraph))
Here is the complete major mode function definition for Text mode:
(defun text-mode ()
"Major mode for editing text intended for humans to read@enddots{}
Special commands: \\{text-mode-map}
Turning on text-mode runs the hook `text-mode-hook'."
(interactive)
(kill-all-local-variables)
(use-local-map text-mode-map)
(setq local-abbrev-table text-mode-abbrev-table)
(set-syntax-table text-mode-syntax-table)
(make-local-variable 'paragraph-start)
(setq paragraph-start (concat "[ \t]*$\\|" page-delimiter))
(make-local-variable 'paragraph-separate)
(setq paragraph-separate paragraph-start)
(setq mode-name "Text")
(setq major-mode 'text-mode)
(run-hooks 'text-mode-hook)) ; Finally, this permits the user to
; customize the mode with a hook.
The three Lisp modes (Lisp mode, Emacs Lisp mode, and Lisp Interaction mode) have more features than Text mode and the code is correspondingly more complicated. Here are excerpts from `lisp-mode.el' that illustrate how these modes are written.
;; Create mode-specific table variables.
(defvar lisp-mode-syntax-table nil "")
(defvar emacs-lisp-mode-syntax-table nil "")
(defvar lisp-mode-abbrev-table nil "")
(if (not emacs-lisp-mode-syntax-table) ; Do not change the table
; if it is already set.
(let ((i 0))
(setq emacs-lisp-mode-syntax-table (make-syntax-table))
;; Set syntax of chars up to 0 to class of chars that are
;; part of symbol names but not words.
;; (The number 0 is 48 in the ASCII character set.)
(while (< i ?0)
(modify-syntax-entry i "_ " emacs-lisp-mode-syntax-table)
(setq i (1+ i)))
...
;; Set the syntax for other characters.
(modify-syntax-entry ? " " emacs-lisp-mode-syntax-table)
(modify-syntax-entry ?\t " " emacs-lisp-mode-syntax-table)
...
(modify-syntax-entry ?\( "() " emacs-lisp-mode-syntax-table)
(modify-syntax-entry ?\) ")( " emacs-lisp-mode-syntax-table)
...))
;; Create an abbrev table for lisp-mode.
(define-abbrev-table 'lisp-mode-abbrev-table ())
Much code is shared among the three Lisp modes. The following function sets various variables; it is called by each of the major Lisp mode functions:
(defun lisp-mode-variables (lisp-syntax) (cond (lisp-syntax (set-syntax-table lisp-mode-syntax-table))) (setq local-abbrev-table lisp-mode-abbrev-table) ...
Functions such as forward-paragraph use the value of the
paragraph-start variable. Since Lisp code is different from
ordinary text, the paragraph-start variable needs to be set
specially to handle Lisp. Also, comments are indented in a special
fashion in Lisp and the Lisp modes need their own mode-specific
comment-indent-function. The code to set these variables is the
rest of lisp-mode-variables.
(make-local-variable 'paragraph-start) (setq paragraph-start (concat page-delimiter "\\|$" )) (make-local-variable 'paragraph-separate) (setq paragraph-separate paragraph-start) ... (make-local-variable 'comment-indent-function) (setq comment-indent-function 'lisp-comment-indent))
Each of the different Lisp modes has a slightly different keymap. For
example, Lisp mode binds C-c C-z to run-lisp, but the other
Lisp modes do not. However, all Lisp modes have some commands in
common. The following code sets up the common commands:
(defvar shared-lisp-mode-map ()
"Keymap for commands shared by all sorts of Lisp modes.")
(if shared-lisp-mode-map
()
(setq shared-lisp-mode-map (make-sparse-keymap))
(define-key shared-lisp-mode-map "\e\C-q" 'indent-sexp)
(define-key shared-lisp-mode-map "\177"
'backward-delete-char-untabify))
And here is the code to set up the keymap for Lisp mode:
(defvar lisp-mode-map ()
"Keymap for ordinary Lisp mode@enddots{}")
(if lisp-mode-map
()
(setq lisp-mode-map (make-sparse-keymap))
(set-keymap-parent lisp-mode-map shared-lisp-mode-map)
(define-key lisp-mode-map "\e\C-x" 'lisp-eval-defun)
(define-key lisp-mode-map "\C-c\C-z" 'run-lisp))
Finally, here is the complete major mode function definition for Emacs Lisp mode.
(defun lisp-mode ()
"Major mode for editing Lisp code for Lisps other than GNU Emacs Lisp.
Commands:
Delete converts tabs to spaces as it moves back.
Blank lines separate paragraphs. Semicolons start comments.
\\{lisp-mode-map}
Note that `run-lisp' may be used either to start an inferior Lisp job
or to switch back to an existing one.
Entry to this mode calls the value of `lisp-mode-hook'
if that value is non-nil."
(interactive)
(kill-all-local-variables)
(use-local-map lisp-mode-map) ; Select the mode's keymap.
(setq major-mode 'lisp-mode) ; This is how describe-mode
; finds out what to describe.
(setq mode-name "Lisp") ; This goes into the mode line.
(lisp-mode-variables t) ; This defines various variables.
(setq imenu-case-fold-search t)
(set-syntax-table lisp-mode-syntax-table)
(run-hooks 'lisp-mode-hook)) ; This permits the user to use a
; hook to customize the mode.
Based on information in the file name or in the file itself, Emacs automatically selects a major mode for the new buffer when a file is visited. It also processes local variables specified in the file text.
fundamental-mode function does not
run any hooks; you're not supposed to customize it. (If you want Emacs
to behave differently in Fundamental mode, change the global
state of Emacs.)
set-auto-mode,
then it runs hack-local-variables to parse, and bind or
evaluate as appropriate, the file's local variables.
If the find-file argument to normal-mode is non-nil,
normal-mode assumes that the find-file function is calling
it. In this case, it may process a local variables list at the end of
the file and in the `-*-' line. The variable
enable-local-variables controls whether to do so. See section `Local Variables in Files' in The GNU Emacs Manual, for
the syntax of the local variables section of a file.
If you run normal-mode interactively, the argument
find-file is normally nil. In this case,
normal-mode unconditionally processes any local variables list.
normal-mode uses condition-case around the call to the
major mode function, so errors are caught and reported as a `File
mode specification error', followed by the original error message.
t means process the local variables
lists unconditionally; nil means ignore them; anything else means
ask the user what to do for each file. The default value is t.
In addition to this list, any variable whose name has a non-nil
risky-local-variable property is also ignored.
t means process them
unconditionally; nil means ignore them; anything else means ask
the user what to do for each file. The default value is maybe.
auto-mode-alist), on the
`#!' line (using interpreter-mode-alist), or on the
file's local variables list. However, this function does not look for
the `mode:' local variable near the end of a file; the
hack-local-variables function does that. See section `How Major Modes are Chosen' in The GNU Emacs Manual.
fundamental-mode.
If the value of default-major-mode is nil, Emacs uses
the (previously) current buffer's major mode for the major mode of a new
buffer. However, if that major mode symbol has a mode-class
property with value special, then it is not used for new buffers;
Fundamental mode is used instead. The modes that have this property are
those such as Dired and Rmail that are useful only with text that has
been specially prepared.
default-major-mode. If that variable is nil, it uses
the current buffer's major mode (if that is suitable).
The low-level primitives for creating buffers do not use this function,
but medium-level commands such as switch-to-buffer and
find-file-noselect use it whenever they create buffers.
lisp-interaction-mode.
(regexp .
mode-function).
For example,
(("\\`/tmp/fol/" . text-mode)
("\\.texinfo\\'" . texinfo-mode)
("\\.texi\\'" . texinfo-mode)
("\\.el\\'" . emacs-lisp-mode)
("\\.c\\'" . c-mode)
("\\.h\\'" . c-mode)
...)
When you visit a file whose expanded file name (see section Functions that Expand Filenames) matches a regexp, set-auto-mode calls the
corresponding mode-function. This feature enables Emacs to select
the proper major mode for most files.
If an element of auto-mode-alist has the form (regexp
function t), then after calling function, Emacs searches
auto-mode-alist again for a match against the portion of the file
name that did not match before. This feature is useful for
uncompression packages: an entry of the form ("\\.gz\\'"
function t) can uncompress the file and then put the uncompressed
file in the proper mode according to the name sans `.gz'.
Here is an example of how to prepend several pattern pairs to
auto-mode-alist. (You might use this sort of expression in your
`.emacs' file.)
(setq auto-mode-alist
(append
;; File name (within directory) starts with a dot.
'(("/\\.[^/]*\\'" . fundamental-mode)
;; File name has no dot.
("[^\\./]*\\'" . fundamental-mode)
;; File name ends in `.C'.
("\\.C\\'" . c++-mode))
auto-mode-alist))
(interpreter . mode); for
example, ("perl" . perl-mode) is one element present by default.
The element says to use mode mode if the file specifies
an interpreter which matches interpreter. The value of
interpreter is actually a regular expression.
This variable is applicable only when the auto-mode-alist does
not indicate which major mode to use.
The handling of enable-local-variables documented for
normal-mode actually takes place here. The argument force
usually comes from the argument find-file given to
normal-mode.
The describe-mode function is used to provide information
about major modes. It is normally called with C-h m. The
describe-mode function uses the value of major-mode,
which is why every major mode function needs to set the
major-mode variable.
The describe-mode function calls the documentation
function using the value of major-mode as an argument. Thus, it
displays the documentation string of the major mode function.
(See section Access to Documentation Strings.)
describe-mode function uses the
documentation string of the function as the documentation of the major
mode.
It's often useful to define a new major mode in terms of an existing
one. An easy way to do this is to use define-derived-mode.
The new command variant is defined to call the function parent, then override certain aspects of that parent mode:
variant-map.
define-derived-mode initializes this map to inherit from
parent-map, if it is not already set.
variant-syntax-table.
define-derived-mode initializes this variable by copying
parent-syntax-table, if it is not already set.
variant-abbrev-table.
define-derived-mode initializes this variable by copying
parent-abbrev-table, if it is not already set.
variant-hook,
which it runs in standard fashion as the very last thing that it does.
(The new mode also runs the mode hook of parent as part
of calling parent.)
In addition, you can specify how to override other aspects of
parent with body. The command variant
evaluates the forms in body after setting up all its usual
overrides, just before running variant-hook.
The argument docstring specifies the documentation string for the
new mode. If you omit docstring, define-derived-mode
generates a documentation string.
Here is a hypothetical example:
(define-derived-mode hypertext-mode
text-mode "Hypertext"
"Major mode for hypertext.
\\{hypertext-mode-map}"
(setq case-fold-search nil))
(define-key hypertext-mode-map
[down-mouse-3] 'do-hyper-link)
A minor mode provides features that users may enable or disable independently of the choice of major mode. Minor modes can be enabled individually or in combination. Minor modes would be better named "generally available, optional feature modes," except that such a name would be unwieldy.
A minor mode is not usually a modification of single major mode. For example, Auto Fill mode works with any major mode that permits text insertion. To be general, a minor mode must be effectively independent of the things major modes do.
A minor mode is often much more difficult to implement than a major mode. One reason is that you should be able to activate and deactivate minor modes in any order. A minor mode should be able to have its desired effect regardless of the major mode and regardless of the other minor modes in effect.
Often the biggest problem in implementing a minor mode is finding a way to insert the necessary hook into the rest of Emacs. Minor mode keymaps make this easier than it used to be.
There are conventions for writing minor modes just as there are for major modes. Several of the major mode conventions apply to minor modes as well: those regarding the name of the mode initialization function, the names of global symbols, and the use of keymaps and other tables.
In addition, there are several conventions that are specific to minor modes.
nil to disable; anything else to
enable).
If it is possible, implement the mode so that setting the variable
automatically enables or disables the mode. Then the minor mode command
does not need to do anything except set the variable.
This variable is used in conjunction with the minor-mode-alist to
display the minor mode name in the mode line. It can also enable
or disable a minor mode keymap. Individual commands or hooks can also
check the variable's value.
If you want the minor mode to be enabled separately in each buffer,
make the variable buffer-local.
nil, it should toggle the mode (turn it on if it is off, and off
if it is on). Otherwise, it should turn the mode on if the argument is
a positive integer, a symbol other than nil or -, or a
list whose CAR is such an integer or symbol; it should turn the
mode off otherwise.
Here is an example taken from the definition of transient-mark-mode.
It shows the use of transient-mark-mode as a variable that enables or
disables the mode's behavior, and also shows the proper way to toggle,
enable or disable the minor mode based on the raw prefix argument value.
(setq transient-mark-mode
(if (null arg) (not transient-mark-mode)
(> (prefix-numeric-value arg) 0)))
minor-mode-alist for each minor mode
(see section Variables Used in the Mode Line), if you want to indicate the minor mode in
the mode line. This element should be a list of the following form:
(mode-variable string)Here mode-variable is the variable that controls enabling of the minor mode, and string is a short string, starting with a space, to represent the mode in the mode line. These strings must be short so that there is room for several of them at once. When you add an element to
minor-mode-alist, use assq to
check for an existing element, to avoid duplication. For example:
(or (assq 'leif-mode minor-mode-alist)
(setq minor-mode-alist
(cons '(leif-mode " Leif") minor-mode-alist)))
You can also use add-to-list to add an element to this list
just once (see section How to Alter a Variable Value).
Each minor mode can have its own keymap, which is active when the mode
is enabled. To set up a keymap for a minor mode, add an element to the
alist minor-mode-map-alist. See section Active Keymaps.
One use of minor mode keymaps is to modify the behavior of certain
self-inserting characters so that they do something else as well as
self-insert. In general, this is the only way to do that, since the
facilities for customizing self-insert-command are limited to
special cases (designed for abbrevs and Auto Fill mode). (Do not try
substituting your own definition of self-insert-command for the
standard one. The editor command loop handles this function specially.)
The key sequences bound in a minor mode should consist of C-c followed by a punctuation character other than {, }, <, >, : or ;. (Those few punctuation characters are reserved for major modes.)
The easy-mmode package provides a convenient way of implementing a minor mode; with it, you can specify all about a simple minor mode in one self-contained definition.
This macro defines a command named mode which toggles the minor mode, and has doc as its documentation string.
It also defines a variable named mode, which is set to t or
nil by enabling or disabling the mode. The variable is
initialized to init-value.
The string mode-indicator says what to display in the mode line
when the mode is enabled; if it is nil, the mode is not displayed
in the mode line.
The optional argument keymap specifies the keymap for the minor mode. It can be a variable name, whose value is the keymap, or it can be an alist specifying bindings in this form:
(key-sequence . definition)
Here is an example of using easy-mmode-define-minor-mode:
(easy-mmode-define-minor-mode hungry-mode
"Toggle Hungry mode.
With no argument, this command toggles the mode.
Non-null prefix argument turns on the mode.
Null prefix argument turns off the mode.
When Hungry mode is enabled, the control delete key
gobbles all preceding whitespace except the last.
See the command \\[hungry-electric-delete]."
;; The initial value.
nil
;; The indicator for the mode line.
" Hungry"
;; The minor mode bindings.
'(("\C-\^?" . hungry-electric-delete)
("\C-\M-\^?"
. (lambda ()
(interactive)
(hungry-electric-delete t)))))
This defines a minor mode named "Hungry mode", a command named
hungry-mode to toggle it, a variable named hungry-mode
which indicates whether the mode is enabled, and a variable named
hungry-mode-map which holds the keymap that is active when the
mode is enabled. It initializes the keymap with key bindings for
C-DEL and C-M-DEL.
Each Emacs window (aside from minibuffer windows) includes a mode line, which displays status information about the buffer displayed in the window. The mode line contains information about the buffer, such as its name, associated file, depth of recursive editing, and the major and minor modes.
This section describes how the contents of the mode line are controlled. We include it in this chapter because much of the information displayed in the mode line relates to the enabled major and minor modes.
mode-line-format is a buffer-local variable that holds a
template used to display the mode line of the current buffer. All
windows for the same buffer use the same mode-line-format and
their mode lines appear the same (except for scrolling percentages, and
line and column numbers).
The mode line of a window is normally updated whenever a different
buffer is shown in the window, or when the buffer's modified-status
changes from nil to t or vice-versa. If you modify any of
the variables referenced by mode-line-format (see section Variables Used in the Mode Line), or any other variables and data structures that affect how
text is displayed (see section Emacs Display), you may want to force an update of
the mode line so as to display the new information or display it in
the new way.
The mode line is usually displayed in inverse video; see
mode-line-inverse-video in section Inverse Video.
The mode line contents are controlled by a data structure of lists,
strings, symbols, and numbers kept in the buffer-local variable
mode-line-format. The data structure is called a mode line
construct, and it is built in recursive fashion out of simpler mode line
constructs. The same data structure is used for constructing
frame titles (see section Frame Titles).
A mode line construct may be as simple as a fixed string of text, but it usually specifies how to use other variables to construct the text. Many of these variables are themselves defined to have mode line constructs as their values.
The default value of mode-line-format incorporates the values
of variables such as mode-name and minor-mode-alist.
Because of this, very few modes need to alter mode-line-format
itself. For most purposes, it is sufficient to alter some of the
variables that mode-line-format refers to.
A mode line construct may be a list, a symbol, or a string. If the value is a list, each element may be a list, a symbol, or a string.
string
%-constructs. Decimal digits after the `%'
specify the field width for space filling on the right (i.e., the data
is left justified). See section %-Constructs in the Mode Line.
symbol
t and nil are ignored; so is any
symbol whose value is void.
There is one exception: if the value of symbol is a string, it is
displayed verbatim: the %-constructs are not recognized.
(string rest...) or (list rest...)
(symbol then else)
nil,
the second element, then, is processed recursively as a mode line
element. But if the value of symbol is nil, the third
element, else, is processed recursively. You may omit else;
then the mode line element displays nothing if the value of symbol
is nil.
(width rest...)
(-3 "%p").
If you do alter mode-line-format itself, the new value should
use the same variables that appear in the default value (see section Variables Used in the Mode Line), rather than duplicating their contents or displaying
the information in another fashion. This way, customizations made by
the user or by Lisp programs (such as display-time and major
modes) via changes to those variables remain effective.
Here is an example of a mode-line-format that might be
useful for shell-mode, since it contains the host name and default
directory.
(setq mode-line-format
(list "-"
'mode-line-mule-info
'mode-line-modified
'mode-line-frame-identification
"%b--"
;; Note that this is evaluated while making the list.
;; It makes a mode line construct which is just a string.
(getenv "HOST")
":"
'default-directory
" "
'global-mode-string
" %[("
'mode-name
'mode-line-process
'minor-mode-alist
"%n"
")%]--"
'(which-func-mode ("" which-func-format "--"))
'(line-number-mode "L%l--")
'(column-number-mode "C%c--")
'(-3 . "%p")
"-%-"))
(The variables line-number-mode, column-number-mode
and which-func-mode enable particular minor modes; as usual,
these variable names are also the minor mode command names.)
This section describes variables incorporated by the
standard value of mode-line-format into the text of the mode
line. There is nothing inherently special about these variables; any
other variables could have the same effects on the mode line if
mode-line-format were changed to use them.
The default value of mode-line-modified is ("%1*%1+").
This means that the mode line displays `**' if the buffer is
modified, `--' if the buffer is not modified, `%%' if the
buffer is read only, and `%*' if the buffer is read only and
modified.
Changing this variable does not force an update of the mode line.
" " if you are using a window system which can show multiple
frames, or "-%F " on an ordinary terminal which shows only one
frame at a time.
("%12b"), which displays the buffer name, padded
with spaces to at least 12 columns.
display-time
sets global-mode-string to refer to the variable
display-time-string, which holds a string containing the time and
load information.
The `%M' construct substitutes the value of
global-mode-string, but that is obsolete, since the variable is
included in the mode line from mode-line-format.
minor-mode-alist should be a two-element list:
(minor-mode-variable mode-line-string)
More generally, mode-line-string can be any mode line spec. It
appears in the mode line when the value of minor-mode-variable is
non-nil, and not otherwise. These strings should begin with
spaces so that they don't run together. Conventionally, the
minor-mode-variable for a specific mode is set to a non-nil
value when that minor mode is activated.
The default value of minor-mode-alist is:
minor-mode-alist
=> ((vc-mode vc-mode)
(abbrev-mode " Abbrev")
(overwrite-mode overwrite-mode)
(auto-fill-function " Fill")
(defining-kbd-macro " Def")
(isearch-mode isearch-mode))
minor-mode-alist itself is not buffer-local. Each variable
mentioned in the alist should be buffer-local if its minor mode can be
enabled separately in each buffer.
(":%s"), which allows the shell to display its status along
with the major mode as: `(Shell: run)'. Normally this variable
is nil.
mode-line-format for buffers
that do not override it. This is the same as (default-value
'mode-line-format).
The default value of default-mode-line-format is this list:
("-"
mode-line-mule-info
mode-line-modified
mode-line-frame-identification
mode-line-buffer-identification
" "
global-mode-string
" %[("
mode-name
mode-line-process
minor-mode-alist
"%n"
")%]--"
(which-func-mode ("" which-func-format "--"))
(line-number-mode "L%l--")
(column-number-mode "C%c--")
(-3 . "%p")
"-%-")
vc-mode, buffer-local in each buffer, records
whether the buffer's visited file is maintained with version control,
and, if so, which kind. Its value is nil for no version control,
or a string that appears in the mode line.
%-Constructs in the Mode Line
The following table lists the recognized %-constructs and what
they mean. In any construct except `%%', you can add a decimal
integer after the `%' to specify how many characters to display.
%b
buffer-name function.
See section Buffer Names.
%f
buffer-file-name
function. See section Buffer File Name.
%F
%c
%l
%*
buffer-read-only); buffer-modified-p); %+
buffer-modified-p); buffer-read-only); %&
%s
process-status. See section Process Information.
%t
%p
%P
%n
narrow-to-region in section Narrowing).
%[
%]
%%
%-constructs are allowed.
%-
The following two %-constructs are still supported, but they are
obsolete, since you can get the same results with the variables
mode-name and global-mode-string.
%m
mode-name.
%M
global-mode-string. Currently, only
display-time modifies the value of global-mode-string.
Imenu is a feature that lets users select a definition or section in the buffer, from a menu which lists all of them, to go directly to that location in the buffer. Imenu works by constructing a buffer index which lists the names and positions of the definitions or portions of in the buffer, so the user can pick one of them to move to. This section explains how to customize Imenu for a major mode.
The usual and simplest way is to set the variable
imenu-generic-expression:
nil, specifies regular expressions for
finding definitions for Imenu. In the simplest case, elements should
look like this:
(menu-title regexp subexp)
Here, if menu-title is non-nil, it says that the matches
for this element should go in a submenu of the buffer index;
menu-title itself specifies the name for the submenu. If
menu-title is nil, the matches for this element go directly
in the top level of the buffer index.
The second item in the list, regexp, is a regular expression (see section Regular Expressions); wherever it matches, that is a definition to mention in the buffer index. The third item, subexp, indicates which subexpression in regexp matches the definition's name.
An element can also look like this:
(menu-title regexp index function arguments...)
Each match for this element creates a special index item which, if selected by the user, calls function with arguments item-name, the buffer position, and arguments.
For Emacs Lisp mode, pattern could look like this:
((nil "^\\s-*(def\\(un\\|subst\\|macro\\|advice\\)\
\\s-+\\([-A-Za-z0-9+]+\\)" 2)
("*Vars*" "^\\s-*(def\\(var\\|const\\)\
\\s-+\\([-A-Za-z0-9+]+\\)" 2)
("*Types*"
"^\\s-*\
(def\\(type\\|struct\\|class\\|ine-condition\\)\
\\s-+\\([-A-Za-z0-9+]+\\)" 2))
Setting this variable makes it buffer-local in the current buffer.
t, the default,
means matching should ignore case.
Setting this variable makes it buffer-local in the current buffer.
imenu-generic-expression, to override the syntax table
of the current buffer. Each element should have this form:
(characters . syntax-description)
The CAR, characters, can be either a character or a string.
The element says to give that character or characters the syntax
specified by syntax-description, which is passed to
modify-syntax-entry (see section Syntax Table Functions).
This feature is typically used to give word syntax to characters which
normally have symbol syntax, and thus to simplify
imenu-generic-expression and speed up matching.
For example, Fortran mode uses it this way:
(setq imenu-syntax-alist '(("_$" . "w")))
The imenu-generic-expression patterns can then use `\\sw+'
instead of `\\(\\sw\\|\\s_\\)+'. Note that this technique may be
inconvenient to use when the mode needs to limit the initial character
of a name to a smaller set of characters than are allowed in the rest
of a name.
Setting this variable makes it buffer-local in the current buffer.
Another way to customize Imenu for a major mode is to set the
variables imenu-prev-index-position-function and
imenu-extract-index-name-function:
nil, its value should be a function for
finding the next definition to mention in the buffer index, moving
backwards in the file.
The function should leave point at the place to be connected to the
index item; it should return nil if it doesn't find another item.
Setting this variable makes it buffer-local in the current buffer.
nil, its value should be a function to
return the name for a definition, assuming point is in that definition
as the imenu-prev-index-position-function function would leave
it.
Setting this variable makes it buffer-local in the current buffer.
The last way to customize Imenu for a major mode is to set the
variables imenu-create-index-function:
save-excursion, so where it
leaves point makes no difference.
The default value is a function that uses
imenu-generic-expression to produce the index alist. If you
specify a different function, then imenu-generic-expression is
not used.
Setting this variable makes it buffer-local in the current buffer.
Simple elements in the alist look like (index-name
. index-position). Selecting a simple element has the effect of
moving to position index-position in the buffer.
Special elements look like (index-name position
function arguments...). Selecting a special element
performs
(funcall function index-name position arguments...)
A nested sub-alist element looks like (index-name
sub-alist).
Font Lock mode is a feature that automatically attaches
face properties to certain parts of the buffer based on their
syntactic role. How it parses the buffer depends on the major mode;
most major modes define syntactic criteria for which faces to use, in
which contexts. This section explains how to customize Font Lock for a
particular language--in other words, for a particular major mode.
Font Lock mode finds text to highlight in two ways: through syntactic
parsing based on the syntax table, and through searching (usually for
regular expressions). Syntactic fontification happens first; it finds
comments and string constants, and highlights them using
font-lock-comment-face and font-lock-string-face
(see section Faces for Font Lock); search-based fontification follows.
There are several variables that control how Font Lock mode highlights
text. But major modes should not set any of these variables directly.
Instead, it should set font-lock-defaults as a buffer-local
variable. The value assigned to this variable is used, if and when Font
Lock mode is enabled, to set all the other variables.
(keywords keywords-only case-fold syntax-alist syntax-begin other-vars...)
The first element, keywords, indirectly specifies the value of
font-lock-keywords. It can be a symbol, a variable whose value
is list to use for font-lock-keywords. It can also be a list of
several such symbols, one for each possible level of fontification. The
first symbol specifies how to do level 1 fontification, the second
symbol how to do level 2, and so on.
The second element, keywords-only, specifies the value of the
variable font-lock-keywords-only. If this is non-nil,
syntactic fontification (of strings and comments) is not performed.
The third element, case-fold, specifies the value of
font-lock-case-fold-search. If it is non-nil, Font Lock
mode ignores case when searching as directed by
font-lock-keywords.
If the fourth element, syntax-alist, is non-nil, it should be
a list of cons cells of the form (char-or-string
. string). These are used to set up a syntax table for
fontification (see section Syntax Table Functions). The resulting syntax
table is stored in font-lock-syntax-table.
The fifth element, syntax-begin, specifies the value of
font-lock-beginning-of-syntax-function (see below).
Any further elements other-vars are have form
(variable . value). This kind of element means to
make variable buffer-local and then set it to value. This
is used to set other variables that affect fontification.
The most important variable for customizing Font Lock mode is
font-lock-keywords. It specifies the search criteria for
search-based fontification.
Each element of font-lock-keywords specifies how to find
certain cases of text, and how to highlight those cases. Font Lock mode
processes the elements of font-lock-keywords one by one, and for
each element, it finds and handles all matches. Ordinarily, once
part of the text has been fontified already, this cannot be overridden
by a subsequent match in the same text; but you can specify different
behavior using the override element of a highlighter.
Each element of font-lock-keywords should have one of these
forms:
regexp
font-lock-keyword-face. For example,
;; Highlight discrete occurrences of `foo'
;; using font-lock-keyword-face.
"\\<foo\\>"
The function regexp-opt (see section Syntax of Regular Expressions) is useful for
calculating optimal regular expressions to match a number of different
keywords.
function
font-lock-keyword-face.
When function is called, it receives one argument, the limit of
the search. It should return non-nil if it succeeds, and set the
match data to describe the match that was found.
(matcher . match)
;; Highlight the `bar' in each occurrences of `fubar',
;; using font-lock-keyword-face.
("fu\\(bar\\)" . 1)
If you use regexp-opt to produce the regular expression
matcher, then you can use regexp-opt-depth (see section Syntax of Regular Expressions) to calculate the value for match.
(matcher . facename)
;; Highlight occurrences of `fubar',
;; using the face which is the value of fubar-face.
("fubar" . fubar-face)
(matcher . highlighter)
(subexp facename override laxmatch)The CAR, subexp, is an integer specifying which subexpression of the match to fontify (0 means the entire matching text). The second subelement, facename, specifies the face, as described above. The last two values in highlighter, override and laxmatch, are flags. If override is
t, this element
can override existing fontification made by previous elements of
font-lock-keywords. If it is keep, then each character is
fontified if it has not been fontified already by some other element.
If it is prepend, the face facename is added to the
beginning of the face property. If it is append, the face
facename is added to the end of the face property.
If laxmatch is non-nil, it means there should be no error
if there is no subexpression numbered subexp in matcher.
Here are some examples of elements of this kind, and what they do:
;; Highlight occurrences of either `foo' or `bar', ;; usingfoo-bar-face, even if they have already been highlighted. ;;foo-bar-faceshould be a variable whose value is a face. ("foo\\|bar" 0 foo-bar-face t) ;; Highlight the first subexpression within each occurrences ;; that the functionfubar-matchfinds, ;; using the face which is the value offubar-face. (fubar-match 1 fubar-face)
(matcher highlighters...)
(eval . form)
font-lock-keywords is used in a buffer.
Its value should have one of the forms described in this table.
Warning: Do not design an element of font-lock-keywords
to match text which spans lines; this does not work reliably. While
font-lock-fontify-buffer handles multi-line patterns correctly,
updating when you edit the buffer does not, since it considers text one
line at a time.
This section describes additional variables that a major mode
can set by means of font-lock-defaults.
nil means Font Lock should not fontify comments or strings
syntactically; it should only fontify based on
font-lock-keywords.
nil means that regular expression matching for the sake of
font-lock-keywords should be case-insensitive.
nil, it should be a function to move
point back to a position that is syntactically at "top level" and
outside of strings or comments. Font Lock uses this when necessary
to get the right results for syntactic fontification.
This function is called with no arguments. It should leave point at the
beginning of any enclosing syntactic block. Typical values are
beginning-of-line (i.e., the start of the line is known to be
outside a syntactic block), or beginning-of-defun for programming
modes or backward-paragraph for textual modes (i.e., the
mode-dependent function is known to move outside a syntactic block).
If the value is nil, the beginning of the buffer is used as a
position outside of a syntactic block. This cannot be wrong, but it can
be slow.
nil, it should be a function that is
called with no arguments, to choose an enclosing range of text for
refontification for the command M-g M-g
(font-lock-fontify-block).
The function should report its choice by placing the region around it.
A good choice is a range of text large enough to give proper results,
but not too large so that refontification becomes slow. Typical values
are mark-defun for programming modes or mark-paragraph for
textual modes.
Many major modes offer three different levels of fontification. You
can define multiple levels by using a list of symbols for keywords
in font-lock-defaults. Each symbol specifies one level of
fontification; it is up to the user to choose one of these levels. The
chosen level's symbol value is used to initialize
font-lock-keywords.
Here are the conventions for how to define the levels of fontification:
You can make Font Lock mode use any face, but several faces are
defined specifically for Font Lock mode. Each of these symbols is both
a face name, and a variable whose default value is the symbol itself.
Thus, the default value of font-lock-comment-face is
font-lock-comment-face. This means you can write
font-lock-comment-face in a context such as
font-lock-keywords where a face-name-valued expression is used.
font-lock-comment-face
font-lock-string-face
font-lock-keyword-face
for and if in C.
font-lock-builtin-face
font-lock-function-name-face
font-lock-variable-name-face
font-lock-type-face
font-lock-constant-face
font-lock-warning-face
#error
directives in C.
Font Lock mode can be used to update syntax-table properties
automatically. This is useful in languages for which a single syntax
table by itself is not sufficient.
(matcher subexp syntax override laxmatch)
The parts of this element have the same meanings as in the corresponding
sort of element of font-lock-keywords,
(matcher subexp facename override laxmatch)
However, instead of specifying the value facename to use for the
face property, it specifies the value syntax to use for the
syntax-table property. Here, syntax can be a variable
whose value is a syntax table, a syntax entry of the form
(syntax-code . matching-char), or an expression whose
value is one of those two types.
A hook is a variable where you can store a function or functions to be called on a particular occasion by an existing program. Emacs provides hooks for the sake of customization. Most often, hooks are set up in the `.emacs' file, but Lisp programs can set them also. See section Standard Hooks, for a list of standard hook variables.
Most of the hooks in Emacs are normal hooks. These variables contain lists of functions to be called with no arguments. When the hook name ends in `-hook', that tells you it is normal. We try to make all hooks normal, as much as possible, so that you can use them in a uniform way.
Every major mode function is supposed to run a normal hook called the
mode hook as the last step of initialization. This makes it easy
for a user to customize the behavior of the mode, by overriding the
buffer-local variable assignments already made by the mode. But hooks
are used in other contexts too. For example, the hook
suspend-hook runs just before Emacs suspends itself
(see section Suspending Emacs).
The recommended way to add a hook function to a normal hook is by
calling add-hook (see below). The hook functions may be any of
the valid kinds of functions that funcall accepts (see section What Is a Function?). Most normal hook variables are initially void;
add-hook knows how to deal with this.
If the hook variable's name does not end with `-hook', that indicates it is probably an abnormal hook; you should look at its documentation to see how to use the hook properly.
If the variable's name ends in `-functions' or `-hooks',
then the value is a list of functions, but it is abnormal in that either
these functions are called with arguments or their values are used in
some way. You can use add-hook to add a function to the list,
but you must take care in writing the function. (A few of these
variables are actually normal hooks which were named before we
established the convention of using `-hook' for them.)
If the variable's name ends in `-function', then its value is just a single function, not a list of functions.
Here's an example that uses a mode hook to turn on Auto Fill mode when in Lisp Interaction mode:
(add-hook 'lisp-interaction-mode-hook 'turn-on-auto-fill)
At the appropriate time, Emacs uses the run-hooks function to
run particular hooks. This function calls the hook functions that have
been added with add-hook.
If a hook variable has a non-nil value, that value may be a
function or a list of functions. If the value is a function (either a
lambda expression or a symbol with a function definition), it is called.
If it is a list, the elements are called, in order. The hook functions
are called with no arguments. Nowadays, storing a single function in
the hook variable is semi-obsolete; you should always use a list of
functions.
For example, here's how emacs-lisp-mode runs its mode hook:
(run-hooks 'emacs-lisp-mode-hook)
nil. Then it stops,
and returns nil if some hook function did, and otherwise
returns a non-nil value.
nil. Then it
stops, and returns whatever was returned by the last hook function
that was called.
(add-hook 'text-mode-hook 'my-text-hook-function)
adds my-text-hook-function to the hook called text-mode-hook.
You can use add-hook for abnormal hooks as well as for normal
hooks.
It is best to design your hook functions so that the order in which they
are executed does not matter. Any dependence on the order is "asking
for trouble." However, the order is predictable: normally,
function goes at the front of the hook list, so it will be
executed first (barring another add-hook call). If the optional
argument append is non-nil, the new hook function goes at
the end of the hook list and will be executed last.
If local is non-nil, that says to make the new hook
function buffer-local in the current buffer. Before you can do this, you must
make the hook itself buffer-local by calling make-local-hook
(not make-local-variable). If the hook itself is not
buffer-local, then the value of local makes no difference--the
hook function is always global.
If local is non-nil, that says to remove function
from the buffer-local hook list instead of from the global hook list.
If the hook variable itself is not buffer-local, then the value of
local makes no difference.
hook buffer-local in the
current buffer. When a hook variable is buffer-local, it can have
buffer-local and global hook functions, and run-hooks runs all of
them.
This function works by making t an element of the buffer-local
value. That serves as a flag to use the hook functions in the default
value of the hook variable as well as those in the buffer-local value.
Since run-hooks understands this flag, make-local-hook
works with all normal hooks. It works for only some non-normal
hooks--those whose callers have been updated to understand this meaning
of t.
Do not use make-local-variable directly for hook variables; it is
not sufficient.
GNU Emacs Lisp has convenient on-line help facilities, most of which derive their information from the documentation strings associated with functions and variables. This chapter describes how to write good documentation strings for your Lisp programs, as well as how to write programs to access documentation.
Note that the documentation strings for Emacs are not the same thing as the Emacs manual. Manuals have their own source files, written in the Texinfo language; documentation strings are specified in the definitions of the functions and variables they apply to. A collection of documentation strings is not sufficient as a manual because a good manual is not organized in that fashion; it is organized in terms of topics of discussion.
A documentation string is written using the Lisp syntax for strings, with double-quote characters surrounding the text of the string. This is because it really is a Lisp string object. The string serves as documentation when it is written in the proper place in the definition of a function or variable. In a function definition, the documentation string follows the argument list. In a variable definition, the documentation string follows the initial value of the variable.
When you write a documentation string, make the first line a complete
sentence (or two complete sentences) since some commands, such as
apropos, show only the first line of a multi-line documentation
string. Also, you should not indent the second line of a documentation
string, if it has one, because that looks odd when you use C-h f
(describe-function) or C-h v (describe-variable) to
view the documentation string. See section Tips for Documentation Strings.
Documentation strings can contain several special substrings, which stand for key bindings to be looked up in the current keymaps when the documentation is displayed. This allows documentation strings to refer to the keys for related commands and be accurate even when a user rearranges the key bindings. (See section Access to Documentation Strings.)
In Emacs Lisp, a documentation string is accessible through the function or variable that it describes:
documentation
knows how to extract it.
variable-documentation. The
function documentation-property knows how to retrieve it.
To save space, the documentation for preloaded functions and variables (including primitive functions and autoloaded functions) is stored in the file `emacs/etc/DOC-version'---not inside Emacs. The documentation strings for functions and variables loaded during the Emacs session from byte-compiled files are stored in those files (see section Documentation Strings and Compilation).
The data structure inside Emacs has an integer offset into the file, or
a list containing a file name and an integer, in place of the
documentation string. The functions documentation and
documentation-property use that information to fetch the
documentation string from the appropriate file; this is transparent to
the user.
For information on the uses of documentation strings, see section `Help' in The GNU Emacs Manual.
The `emacs/lib-src' directory contains two utilities that you can use to print nice-looking hardcopy for the file `emacs/etc/DOC-version'. These are `sorted-doc' and `digest-doc'.
substitute-command-keys to substitute actual key bindings. (This
substitution is not done if verbatim is non-nil.)
(documentation-property 'command-line-processed
'variable-documentation)
=> "Non-nil once command line has been processed"
(symbol-plist 'command-line-processed)
=> (variable-documentation 188902)
nil) it calls substitute-command-keys, to return a
value containing the actual (current) key bindings.
The function documentation signals a void-function error
if function has no function definition. However, it is OK if
the function definition has no documentation string. In that case,
documentation returns nil.
Here is an example of using the two functions, documentation and
documentation-property, to display the documentation strings for
several symbols in a `*Help*' buffer.
(defun describe-symbols (pattern)
"Describe the Emacs Lisp symbols matching PATTERN.
All symbols that have PATTERN in their name are described
in the `*Help*' buffer."
(interactive "sDescribe symbols matching: ")
(let ((describe-func
(function
(lambda (s)
;; Print description of symbol.
(if (fboundp s) ; It is a function.
(princ
(format "%s\t%s\n%s\n\n" s
(if (commandp s)
(let ((keys (where-is-internal s)))
(if keys
(concat
"Keys: "
(mapconcat 'key-description
keys " "))
"Keys: none"))
"Function")
(or (documentation s)
"not documented"))))
(if (boundp s) ; It is a variable.
(princ
(format "%s\t%s\n%s\n\n" s
(if (user-variable-p s)
"Option " "Variable")
(or (documentation-property
s 'variable-documentation)
"not documented")))))))
sym-list)
;; Build a list of symbols that match pattern.
(mapatoms (function
(lambda (sym)
(if (string-match pattern (symbol-name sym))
(setq sym-list (cons sym sym-list))))))
;; Display the data.
(with-output-to-temp-buffer "*Help*"
(mapcar describe-func (sort sym-list 'string<))
(print-help-return-message))))
The describe-symbols function works like apropos,
but provides more information.
(describe-symbols "goal") ---------- Buffer: *Help* ---------- goal-column Option *Semipermanent goal column for vertical motion, as set by ... set-goal-column Keys: C-x C-n Set the current horizontal position as a goal for C-n and C-p. Those commands will move to this position in the line moved to rather than trying to keep the same horizontal position. With a non-nil argument, clears out the goal column so that C-n and C-p resume vertical motion. The goal column is stored in the variable `goal-column'. temporary-goal-column Variable Current goal column for vertical motion. It is the column where point was at the start of current run of vertical motion commands. When the `track-eol' feature is doing its job, the value is 9999. ---------- Buffer: *Help* ----------
Emacs reads the file filename from the `emacs/etc' directory.
When the dumped Emacs is later executed, the same file will be looked
for in the directory doc-directory. Usually filename is
"DOC-version".
"DOC-version" that contains documentation strings for
built-in and preloaded functions and variables.
In most cases, this is the same as data-directory. They may be
different when you run Emacs from the directory where you built it,
without actually installing it. See data-directory in section Help Functions.
In older Emacs versions, exec-directory was used for this.
When documentation strings refer to key sequences, they should use the
current, actual key bindings. They can do so using certain special text
sequences described below. Accessing documentation strings in the usual
way substitutes current key binding information for these special
sequences. This works by calling substitute-command-keys. You
can also call that function yourself.
Here is a list of the special sequences and what they mean:
\[command]
\{mapvar}
describe-bindings.
\<mapvar>
\=
Please note: Each `\' must be doubled when written in a string in Emacs Lisp.
Here are examples of the special sequences:
(substitute-command-keys
"To abort recursive edit, type: \\[abort-recursive-edit]")
=> "To abort recursive edit, type: C-]"
(substitute-command-keys
"The keys that are defined for the minibuffer here are:
\\{minibuffer-local-must-match-map}")
=> "The keys that are defined for the minibuffer here are:
? minibuffer-completion-help
SPC minibuffer-complete-word
TAB minibuffer-complete
C-j minibuffer-complete-and-exit
RET minibuffer-complete-and-exit
C-g abort-recursive-edit
"
(substitute-command-keys
"To abort a recursive edit from the minibuffer, type\
\\<minibuffer-local-must-match-map>\\[abort-recursive-edit].")
=> "To abort a recursive edit from the minibuffer, type C-g."
These functions convert events, key sequences, or characters to textual descriptions. These descriptions are useful for including arbitrary text characters or key sequences in messages, because they convert non-printing and whitespace characters to sequences of printing characters. The description of a non-whitespace printing character is the character itself.
single-key-description, below.
(single-key-description ?\C-x)
=> "C-x"
(key-description "\C-x \M-y \n \t \r \f123")
=> "C-x SPC M-y SPC C-j SPC TAB SPC RET SPC C-l 1 2 3"
(single-key-description 'C-mouse-1)
=> "C-mouse-1"
single-key-description, except that control characters are
represented with a leading caret (which is how control characters in
Emacs buffers are usually displayed).
(text-char-description ?\C-c)
=> "^C"
(text-char-description ?\M-m)
=> "M-m"
(text-char-description ?\C-\M-m)
=> "M-^M"
key-description. You
call it with a string containing key descriptions, separated by spaces;
it returns a string or vector containing the corresponding events.
(This may or may not be a single valid key sequence, depending on what
events you use; see section Keymap Terminology.)
Emacs provides a variety of on-line help functions, all accessible to the user as subcommands of the prefix C-h. For more information about them, see section `Help' in The GNU Emacs Manual. Here we describe some program-level interfaces to the same information.
If do-all is non-nil, then apropos also shows key
bindings for the functions that are found; it also shows all symbols,
even those that are neither functions nor variables.
In the first of the following examples, apropos finds all the
symbols with names containing `exec'. (We don't show here the
output that results in the `*Help*' buffer.)
(apropos "exec")
=> (Buffer-menu-execute command-execute exec-directory
exec-path execute-extended-command execute-kbd-macro
executing-kbd-macro executing-macro)
help-map. It is defined in `help.el' as
follows:
(define-key global-map "\C-h" 'help-command) (fset 'help-command help-map)
nil.
Otherwise it calls message to display it in the echo area.
This function expects to be called inside a
with-output-to-temp-buffer special form, and expects
standard-output to have the value bound by that special form.
For an example of its use, see the long example in section Access to Documentation Strings.
help-form is a non-nil Lisp expression, it evaluates that
expression, and displays the result in a window if it is a string.
Usually the value of help-form is nil. Then the
help character has no special meaning at the level of command input, and
it becomes part of a key sequence in the normal way. The standard key
binding of C-h is a prefix key for several general-purpose help
features.
The help character is special after prefix keys, too. If it has no
binding as a subcommand of the prefix key, it runs
describe-prefix-bindings, which displays a list of all the
subcommands of the prefix key.
help-char.
nil, its value is a form to evaluate
whenever the character help-char is read. If evaluating the form
produces a string, that string is displayed.
A command that calls read-event or read-char probably
should bind help-form to a non-nil expression while it
does input. (The time when you should not do this is when C-h has
some other meaning.) Evaluating this expression should result in a
string that explains what the input is for and how to enter it properly.
Entry to the minibuffer binds this variable to the value of
minibuffer-help-form (see section Minibuffer Miscellany).
describe-prefix-bindings.
describe-bindings to display a list of all
the subcommands of the prefix key of the most recent key sequence. The
prefix described consists of all but the last event of that key
sequence. (The last event is, presumably, the help character.)
The following two functions are meant for modes that want to provide help without relinquishing control, such as the "electric" modes. Their names begin with `Helper' to distinguish them from the ordinary help functions.
describe-bindings.
nil.
This can be customized by changing the map Helper-help-map.
exec-directory was used for this.
When invoked, fname displays help-text in a window, then reads and executes a key sequence according to help-map. The string help-text should describe the bindings available in help-map.
The command fname is defined to handle a few events itself, by scrolling the display of help-text. When fname reads one of those special events, it does the scrolling and then reads another event. When it reads an event that is not one of those few, and which has a binding in help-map, it executes that key's binding and then returns.
The argument help-line should be a single-line summary of the
alternatives in help-map. In the current version of Emacs, this
argument is used only if you set the option three-step-help to
t.
This macro is used in the command help-for-help which is the
binding of C-h C-h.
nil, commands defined with
make-help-screen display their help-line strings in the
echo area at first, and display the longer help-text strings only
if the user types the help character again.
In Emacs, you can find, create, view, save, and otherwise work with files and file directories. This chapter describes most of the file-related functions of Emacs Lisp, but a few others are described in section Buffers, and those related to backups and auto-saving are described in section Backups and Auto-Saving.
Many of the file functions take one or more arguments that are file
names. A file name is actually a string. Most of these functions
expand file name arguments by calling expand-file-name, so that
`~' is handled correctly, as are relative file names (including
`../'). These functions don't recognize environment variable
substitutions such as `$HOME'. See section Functions that Expand Filenames.
Visiting a file means reading a file into a buffer. Once this is done, we say that the buffer is visiting that file, and call the file "the visited file" of the buffer.
A file and a buffer are two different things. A file is information recorded permanently in the computer (unless you delete it). A buffer, on the other hand, is information inside of Emacs that will vanish at the end of the editing session (or when you kill the buffer). Usually, a buffer contains information that you have copied from a file; then we say the buffer is visiting that file. The copy in the buffer is what you modify with editing commands. Such changes to the buffer do not change the file; therefore, to make the changes permanent, you must save the buffer, which means copying the altered buffer contents back into the file.
In spite of the distinction between files and buffers, people often refer to a file when they mean a buffer and vice-versa. Indeed, we say, "I am editing a file," rather than, "I am editing a buffer that I will soon save as a file of the same name." Humans do not usually need to make the distinction explicit. When dealing with a computer program, however, it is good to keep the distinction in mind.
This section describes the functions normally used to visit files. For historical reasons, these functions have names starting with `find-' rather than `visit-'. See section Buffer File Name, for functions and variables that access the visited file name of a buffer or that find an existing buffer by its visited file name.
In a Lisp program, if you want to look at the contents of a file but
not alter it, the fastest way is to use insert-file-contents in a
temporary buffer. Visiting the file is not necessary and takes longer.
See section Reading from Files.
The body of the find-file function is very simple and looks
like this:
(switch-to-buffer (find-file-noselect filename))
(See switch-to-buffer in section Displaying Buffers in Windows.)
When find-file is called interactively, it prompts for
filename in the minibuffer.
When find-file-noselect uses an existing buffer, it first
verifies that the file has not changed since it was last visited or
saved in that buffer. If the file has changed, then this function asks
the user whether to reread the changed file. If the user says
`yes', any changes previously made in the buffer are lost.
This function displays warning or advisory messages in various peculiar
cases, unless the optional argument nowarn is non-nil. For
example, if it needs to create a buffer, and there is no file named
filename, it displays the message `New file' in the echo
area, and leaves the buffer empty.
The find-file-noselect function normally calls
after-find-file after reading the file (see section Subroutines of Visiting). That function sets the buffer major mode, parses local
variables, warns the user if there exists an auto-save file more recent
than the file just visited, and finishes by running the functions in
find-file-hooks.
If the optional argument rawfile is non-nil, then
after-find-file is not called, and the
find-file-not-found-hooks are not run in case of failure. What's
more, a non-nil rawfile value suppresses coding system
conversion (see section Coding Systems) and format conversion (see section File Format Conversion).
The find-file-noselect function returns the buffer that is
visiting the file filename.
(find-file-noselect "/etc/fstab")
=> #<buffer fstab>
When this command is called interactively, it prompts for filename.
find-file, but it marks the buffer as read-only. See section Read-Only Buffers, for related functions and variables.
When this command is called interactively, it prompts for filename.
view-mode-hook. See section Hooks.
When view-file is called interactively, it prompts for
filename.
This variable works just like a normal hook, but we think that renaming it would not be advisable. See section Hooks.
find-file or find-file-noselect is passed a nonexistent
file name. find-file-noselect calls these functions as soon as
it detects a nonexistent file. It calls them in the order of the list,
until one of them returns non-nil. buffer-file-name is
already set up.
This is not a normal hook because the values of the functions are used, and in many cases only some of the functions are called.
The find-file-noselect function uses two important subroutines
which are sometimes useful in user Lisp code: create-file-buffer
and after-find-file. This section explains how to use them.
Please note: create-file-buffer does not
associate the new buffer with a file and does not select the buffer.
It also does not use the default major mode.
(create-file-buffer "foo")
=> #<buffer foo>
(create-file-buffer "foo")
=> #<buffer foo<2>>
(create-file-buffer "foo")
=> #<buffer foo<3>>
This function is used by find-file-noselect.
It uses generate-new-buffer (see section Creating Buffers).
find-file-noselect
and by the default revert function (see section Reverting).
If reading the file got an error because the file does not exist, but
its directory does exist, the caller should pass a non-nil value
for error. In that case, after-find-file issues a warning:
`(New File)'. For more serious errors, the caller should usually not
call after-find-file.
If warn is non-nil, then this function issues a warning
if an auto-save file exists and is more recent than the visited file.
The last thing after-find-file does is call all the functions
in the list find-file-hooks.
When you edit a file in Emacs, you are actually working on a buffer that is visiting that file--that is, the contents of the file are copied into the buffer and the copy is what you edit. Changes to the buffer do not change the file until you save the buffer, which means copying the contents of the buffer into the file.
save-buffer is responsible for making backup files. Normally,
backup-option is nil, and save-buffer makes a backup
file only if this is the first save since visiting the file. Other
values for backup-option request the making of backup files in
other circumstances:
save-buffer function marks this version of the file to be
backed up when the buffer is next saved.
save-buffer function unconditionally backs up the previous
version of the file before saving it.
nil, it saves all the file-visiting buffers without querying
the user.
The optional exiting argument, if non-nil, requests this
function to offer also to save certain other buffers that are not
visiting files. These are buffers that have a non-nil
buffer-local value of buffer-offer-save. (A user who says yes to
saving one of these is asked to specify a file name to use.) The
save-buffers-kill-emacs function passes a non-nil value
for this argument.
set-visited-file-name (see section Buffer File Name) and
save-buffer.
Saving a buffer runs several hooks. It also performs format conversion (see section File Format Conversion), and may save text properties in "annotations" (see section Saving Text Properties in Files).
nil, the file is considered already written and the rest of
the functions are not called, nor is the usual code for writing the file
executed.
If a function in write-file-hooks returns non-nil, it
is responsible for making a backup file (if that is appropriate).
To do so, execute the following code:
(or buffer-backed-up (backup-buffer))
You might wish to save the file modes value returned by
backup-buffer and use that to set the mode bits of the file that
you write. This is what save-buffer normally does.
The hook functions in write-file-hooks are also responsible for
encoding the data (if desired): they must choose a suitable coding
system (see section Coding Systems in Lisp), perform the encoding
(see section Explicit Encoding and Decoding), and set last-coding-system-used to
the coding system that was used (see section Encoding and I/O).
Do not make this variable buffer-local. To set up buffer-specific hook
functions, use write-contents-hooks instead.
Even though this is not a normal hook, you can use add-hook and
remove-hook to manipulate the list. See section Hooks.
write-file-hooks, but it is intended to be
made buffer-local in particular buffers, and used for hooks that pertain
to the file name or the way the buffer contents were obtained.
The variable is marked as a permanent local, so that changing the major mode does not alter a buffer-local value. This is convenient for packages that read "file" contents in special ways, and set up hooks to save the data in a corresponding way.
write-file-hooks, but it is intended for
hooks that pertain to the contents of the file, as opposed to hooks that
pertain to where the file came from. Such hooks are usually set up by
major modes, as buffer-local bindings for this variable.
This variable automatically becomes buffer-local whenever it is set;
switching to a new major mode always resets this variable. When you use
add-hooks to add an element to this hook, you should not
specify a non-nil local argument, since this variable is
used only buffer-locally.
nil, then save-buffer protects
against I/O errors while saving by writing the new file to a temporary
name instead of the name it is supposed to have, and then renaming it to
the intended name after it is clear there are no errors. This procedure
prevents problems such as a lack of disk space from resulting in an
invalid file.
As a side effect, backups are necessarily made by copying. See section Backup by Renaming or by Copying?. Yet, at the same time, saving a precious file always breaks all hard links between the file you save and other file names.
Some modes give this variable a non-nil buffer-local value
in particular buffers.
t, then save-buffer silently adds a newline at the end of
the file whenever the buffer being saved does not already end in one.
If the value of the variable is non-nil, but not t, then
save-buffer asks the user whether to add a newline each time the
case arises.
If the value of the variable is nil, then save-buffer
doesn't add newlines at all. nil is the default value, but a few
major modes set it to t in particular buffers.
See also the function set-visited-file-name (see section Buffer File Name).
You can copy a file from the disk and insert it into a buffer
using the insert-file-contents function. Don't use the user-level
command insert-file in a Lisp program, as that sets the mark.
The function insert-file-contents checks the file contents
against the defined file formats, and converts the file contents if
appropriate. See section File Format Conversion. It also calls the functions in
the list after-insert-file-functions; see section Saving Text Properties in Files.
If visit is non-nil, this function additionally marks the
buffer as unmodified and sets up various fields in the buffer so that it
is visiting the file filename: these include the buffer's visited
file name and its last save file modtime. This feature is used by
find-file-noselect and you probably should not use it yourself.
If beg and end are non-nil, they should be integers
specifying the portion of the file to insert. In this case, visit
must be nil. For example,
(insert-file-contents filename nil 0 500)
inserts the first 500 characters of a file.
If the argument replace is non-nil, it means to replace the
contents of the buffer (actually, just the accessible portion) with the
contents of the file. This is better than simply deleting the buffer
contents and inserting the whole file, because (1) it preserves some
marker positions and (2) it puts less data in the undo list.
It is possible to read a special file (such as a FIFO or an I/O device)
with insert-file-contents, as long as replace and
visit are nil.
insert-file-contents except that it does
not do format decoding (see section File Format Conversion), does not do
character code conversion (see section Coding Systems), does not run
find-file-hooks, does not perform automatic uncompression, and so
on.
If you want to pass a file name to another process so that another
program can read the file, use the function file-local-copy; see
section Making Certain File Names "Magic".
You can write the contents of a buffer, or part of a buffer, directly
to a file on disk using the append-to-file and
write-region functions. Don't use these functions to write to
files that are being visited; that could cause confusion in the
mechanisms for visiting.
nil.
An error is signaled if filename specifies a nonwritable file, or a nonexistent file in a directory where files cannot be created.
If start is a string, then write-region writes or appends
that string, rather than text from the buffer.
If append is non-nil, then the specified text is appended
to the existing file contents (if any).
If confirm is non-nil, then write-region asks
for confirmation if filename names an existing file.
If visit is t, then Emacs establishes an association
between the buffer and the file: the buffer is then visiting that file.
It also sets the last file modification time for the current buffer to
filename's modtime, and marks the buffer as not modified. This
feature is used by save-buffer, but you probably should not use
it yourself.
If visit is a string, it specifies the file name to visit. This
way, you can write the data to one file (filename) while recording
the buffer as visiting another file (visit). The argument
visit is used in the echo area message and also for file locking;
visit is stored in buffer-file-name. This feature is used
to implement file-precious-flag; don't use it yourself unless you
really know what you're doing.
The function write-region converts the data which it writes to
the appropriate file formats specified by buffer-file-format.
See section File Format Conversion. It also calls the functions in the list
write-region-annotate-functions; see section Saving Text Properties in Files.
Normally, write-region displays the message `Wrote
filename' in the echo area. If visit is neither t
nor nil nor a string, then this message is inhibited. This
feature is useful for programs that use files for internal purposes,
files that the user does not need to know about.
with-temp-file macro evaluates the body forms with a
temporary buffer as the current buffer; then, at the end, it writes the
buffer contents into file file. It kills the temporary buffer
when finished, restoring the buffer that was current before the
with-temp-file form. Then it returns the value of the last form
in body.
The current buffer is restored even in case of an abnormal exit via
throw or error (see section Nonlocal Exits).
See also with-temp-buffer in section The Current Buffer.
When two users edit the same file at the same time, they are likely to interfere with each other. Emacs tries to prevent this situation from arising by recording a file lock when a file is being modified. Emacs can then detect the first attempt to modify a buffer visiting a file that is locked by another Emacs job, and ask the user what to do.
File locks are not completely reliable when multiple machines can share file systems. When file locks do not work, it is possible for two users to make changes simultaneously, but Emacs can still warn the user who saves second. Also, the detection of modification of a buffer visiting a file changed on disk catches some cases of simultaneous editing; see section Comparison of Modification Time.
nil if the file filename is not
locked. It returns t if it is locked by this Emacs process, and
it returns the name of the user who has locked it if it is locked by
some other job.
(file-locked-p "foo")
=> nil
t says to grab the lock on the file. Then
this user may edit the file and other-user loses the lock.
nil says to ignore the lock and let this
user edit the file anyway.
file-locked error, in which
case the change that the user was about to make does not take place.
The error message for this error looks like this:
error--> File is locked: file other-userwhere
file is the name of the file and other-user is the
name of the user who has locked the file.
If you wish, you can replace the ask-user-about-lock function
with your own version that makes the decision in another way. The code
for its usual definition is in `userlock.el'.
The functions described in this section all operate on strings that designate file names. All the functions have names that begin with the word `file'. These functions all return information about actual files or directories, so their arguments must all exist as actual files or directories unless otherwise noted.
These functions test for permission to access a file in specific ways.
t if a file named filename appears
to exist. This does not mean you can necessarily read the file, only
that you can find out its attributes. (On Unix, this is true if the
file exists and you have execute permission on the containing
directories, regardless of the protection of the file itself.)
If the file does not exist, or if fascist access control policies
prevent you from finding the attributes of the file, this function
returns nil.
t if a file named filename exists
and you can read it. It returns nil otherwise.
(file-readable-p "files.texi")
=> t
(file-exists-p "/usr/spool/mqueue")
=> t
(file-readable-p "/usr/spool/mqueue")
=> nil
t if a file named filename exists and
you can execute it. It returns nil otherwise. If the file is a
directory, execute permission means you can check the existence and
attributes of files inside the directory, and open those files if their
modes permit.
t if the file filename can be written
or created by you, and nil otherwise. A file is writable if the
file exists and you can write it. It is creatable if it does not exist,
but the specified directory does exist and you can write in that
directory.
In the third example below, `foo' is not writable because the parent directory does not exist, even though the user could create such a directory.
(file-writable-p "~/foo")
=> t
(file-writable-p "/foo")
=> nil
(file-writable-p "~/no-such-dir/foo")
=> nil
t if you have permission to open existing
files in the directory whose name as a file is dirname; otherwise
(or if there is no such directory), it returns nil. The value
of dirname may be either a directory name or the file name of a
file which is a directory.
Example: after the following,
(file-accessible-directory-p "/foo")
=> nil
we can deduce that any attempt to read a file in `/foo/' will give an error.
nil. However, if the open fails, it signals an error
using string as the error message text.
t if deleting the file filename and
then creating it anew would keep the file's owner unchanged.
t if the file filename1 is
newer than file filename2. If filename1 does not
exist, it returns nil. If filename2 does not exist,
it returns t.
In the following example, assume that the file `aug-19' was written on the 19th, `aug-20' was written on the 20th, and the file `no-file' doesn't exist at all.
(file-newer-than-file-p "aug-19" "aug-20")
=> nil
(file-newer-than-file-p "aug-20" "aug-19")
=> t
(file-newer-than-file-p "aug-19" "no-file")
=> t
(file-newer-than-file-p "no-file" "aug-19")
=> nil
You can use file-attributes to get a file's last modification
time as a list of two numbers. See section Other Information about Files.
This section describes how to distinguish various kinds of files, such as directories, symbolic links, and ordinary files.
file-symlink-p
function returns the file name to which it is linked. This may be the
name of a text file, a directory, or even another symbolic link, or it
may be a nonexistent file name.
If the file filename is not a symbolic link (or there is no such file),
file-symlink-p returns nil.
(file-symlink-p "foo")
=> nil
(file-symlink-p "sym-link")
=> "foo"
(file-symlink-p "sym-link2")
=> "sym-link"
(file-symlink-p "/bin")
=> "/pub/bin"
t if filename is the name of an
existing directory, nil otherwise.
(file-directory-p "~rms")
=> t
(file-directory-p "~rms/lewis/files.texi")
=> nil
(file-directory-p "~rms/lewis/no-such-file")
=> nil
(file-directory-p "$HOME")
=> nil
(file-directory-p
(substitute-in-file-name "$HOME"))
=> t
t if the file filename exists and is
a regular file (not a directory, symbolic link, named pipe, terminal, or
other I/O device).
The truename of a file is the name that you get by following symbolic links until none remain, then simplifying away `.' and `..' appearing as components. Strictly speaking, a file need not have a unique truename; the number of distinct truenames a file has is equal to the number of hard links to the file. However, truenames are useful because they eliminate symbolic links as a cause of name variation.
file-truename returns the true name of the file
filename. This is the name that you get by following symbolic
links until none remain. The argument must be an absolute file name.
See section Buffer File Name, for related information.
This section describes the functions for getting detailed information about a file, other than its contents. This information includes the mode bits that control access permission, the owner and group numbers, the number of names, the inode number, the size, and the times of access and modification.
The highest value returnable is 4095 (7777 octal), meaning that everyone has read, write, and execute permission, that the SUID bit is set for both others and group, and that the sticky bit is set.
(file-modes "~/junk/diffs")
=> 492 ; Decimal integer.
(format "%o" 492)
=> "754" ; Convert to octal.
(set-file-modes "~/junk/diffs" 438)
=> nil
(format "%o" 438)
=> "666" ; Convert to octal.
% ls -l diffs
-rw-rw-rw- 1 lewis 0 3063 Oct 30 16:00 diffs
nil. Note that symbolic links have no effect on this
function, because they are not considered to be names of the files they
link to.
% ls -l foo*
-rw-rw-rw- 2 rms 4 Aug 19 01:27 foo
-rw-rw-rw- 2 rms 4 Aug 19 01:27 foo1
(file-nlinks "foo")
=> 2
(file-nlinks "doesnt-exist")
=> nil
nil.
The elements of the list, in order, are:
t for a directory, a string for a symbolic link (the name
linked to), or nil for a text file.
add-name-to-file function
(see section Changing File Names and Attributes).
current-time; see section Time of Day.)
t if the file's GID would change if file were
deleted and recreated; nil otherwise.
(high . low), where low
holds the low 16 bits.
For example, here are the file attributes for `files.texi':
(file-attributes "files.texi")
=> (nil 1 2235 75
(8489 20284)
(8489 20284)
(8489 20285)
14906 "-rw-rw-rw-"
nil 129500 -32252)
and here is how the result is interpreted:
nil
1
2235
75
(8489 20284)
(8489 20284)
(8489 20285)
14906
"-rw-rw-rw-"
nil
129500
-32252
The functions in this section rename, copy, delete, link, and set the modes of files.
In the functions that have an argument newname, if a file by the name of newname already exists, the actions taken depend on the value of the argument ok-if-already-exists:
file-already-exists error if
ok-if-already-exists is nil.
In the first part of the following example, we list two files, `foo' and `foo3'.
% ls -li fo* 81908 -rw-rw-rw- 1 rms 29 Aug 18 20:32 foo 84302 -rw-rw-rw- 1 rms 24 Aug 18 20:31 foo3
Now we create a hard link, by calling add-name-to-file, then list
the files again. This shows two names for one file, `foo' and
`foo2'.
(add-name-to-file "foo" "foo2")
=> nil
% ls -li fo*
81908 -rw-rw-rw- 2 rms 29 Aug 18 20:32 foo
81908 -rw-rw-rw- 2 rms 29 Aug 18 20:32 foo2
84302 -rw-rw-rw- 1 rms 24 Aug 18 20:31 foo3
Finally, we evaluate the following:
(add-name-to-file "foo" "foo3" t)
and list the files again. Now there are three names for one file: `foo', `foo2', and `foo3'. The old contents of `foo3' are lost.
(add-name-to-file "foo1" "foo3")
=> nil
% ls -li fo*
81908 -rw-rw-rw- 3 rms 29 Aug 18 20:32 foo
81908 -rw-rw-rw- 3 rms 29 Aug 18 20:32 foo2
81908 -rw-rw-rw- 3 rms 29 Aug 18 20:32 foo3
This function is meaningless on operating systems where multiple names for one file are not allowed.
See also file-nlinks in section Other Information about Files.
If filename has additional names aside from filename, it
continues to have those names. In fact, adding the name newname
with add-name-to-file and then deleting filename has the
same effect as renaming, aside from momentary intermediate states.
In an interactive call, this function prompts for filename and newname in the minibuffer; also, it requests confirmation if newname already exists.
If time is non-nil, then this function gives the new file
the same last-modified time that the old one has. (This works on only
some operating systems.) If setting the time gets an error,
copy-file signals a file-date-error error.
In an interactive call, this function prompts for filename and newname in the minibuffer; also, it requests confirmation if newname already exists.
A suitable kind of file-error error is signaled if the file
does not exist, or is not deletable. (On Unix, a file is deletable if
its directory is writable.)
See also delete-directory in section Creating and Deleting Directories.
In an interactive call, this function prompts for filename and newname in the minibuffer; also, it requests confirmation if newname already exists.
The argument mode must be an integer. On most systems, only the low 9 bits of mode are meaningful.
Saving a modified version of an existing file does not count as creating the file; it does not change the file's mode, and does not use the default file protection.
On MS-DOS, there is no such thing as an "executable" file mode bit.
So Emacs considers a file executable if its name ends in `.com',
`.bat' or `.exe'. This is reflected in the values returned
by file-modes and file-attributes.
Files are generally referred to by their names, in Emacs as elsewhere. File names in Emacs are represented as strings. The functions that operate on a file all expect a file name argument.
In addition to operating on files themselves, Emacs Lisp programs often need to operate on file names; i.e., to take them apart and to use part of a name to construct related file names. This section describes how to manipulate file names.
The functions in this section do not actually access files, so they can operate on file names that do not refer to an existing file or directory.
On VMS, all these functions understand both VMS file-name syntax and Unix syntax. This is so that all the standard Lisp libraries can specify file names in Unix syntax and work properly on VMS without change. On MS-DOS and MS-Windows, these functions understand MS-DOS or MS-Windows file-name syntax as well as Unix syntax.
The operating system groups files into directories. To specify a file, you must specify the directory and the file's name within that directory. Therefore, Emacs considers a file name as having two main parts: the directory name part, and the nondirectory part (or file name within the directory). Either part may be empty. Concatenating these two parts reproduces the original file name.
On Unix, the directory part is everything up to and including the last slash; the nondirectory part is the rest. The rules in VMS syntax are complicated.
For some purposes, the nondirectory part is further subdivided into the name proper and the version number. On Unix, only backup files have version numbers in their names. On VMS, every file has a version number, but most of the time the file name actually used in Emacs omits the version number, so that version numbers in Emacs are found mostly in directory lists.
nil if filename does not include a directory part). On
Unix, the function returns a string ending in a slash. On VMS, it
returns a string ending in one of the three characters `:',
`]', or `>'.
(file-name-directory "lewis/foo") ; Unix example
=> "lewis/"
(file-name-directory "foo") ; Unix example
=> nil
(file-name-directory "[X]FOO.TMP") ; VMS example
=> "[X]"
(file-name-nondirectory "lewis/foo")
=> "foo"
(file-name-nondirectory "foo")
=> "foo"
;; The following example is accurate only on VMS.
(file-name-nondirectory "[X]FOO.TMP")
=> "FOO.TMP"
(file-name-sans-versions "~rms/foo.~1~")
=> "~rms/foo"
(file-name-sans-versions "~rms/foo~")
=> "~rms/foo"
(file-name-sans-versions "~rms/foo")
=> "~rms/foo"
;; The following example applies to VMS only.
(file-name-sans-versions "foo;23")
=> "foo"
(file-name-sans-extension "foo.lose.c")
=> "foo.lose"
(file-name-sans-extension "big.hack/foo")
=> "big.hack/foo"
A directory name is the name of a directory. A directory is a kind of file, and it has a file name, which is related to the directory name but not identical to it. (This is not quite the same as the usual Unix terminology.) These two different names for the same entity are related by a syntactic transformation. On Unix, this is simple: a directory name ends in a slash, whereas the directory's name as a file lacks that slash. On VMS, the relationship is more complicated.
The difference between a directory name and its name as a file is subtle but crucial. When an Emacs variable or function argument is described as being a directory name, a file name of a directory is not acceptable.
The following two functions convert between directory names and file names. They do nothing special with environment variable substitutions such as `$HOME', and the constructs `~', and `..'.
(file-name-as-directory "~rms/lewis")
=> "~rms/lewis/"
(directory-file-name "~lewis/")
=> "~lewis"
Directory name abbreviations are useful for directories that are normally accessed through symbolic links. Sometimes the users recognize primarily the link's name as "the name" of the directory, and find it annoying to see the directory's "real" name. If you define the link name as an abbreviation for the "real" name, Emacs shows users the abbreviation instead.
directory-abbrev-alist contains an alist of
abbreviations to use for file directories. Each element has the form
(from . to), and says to replace from with
to when it appears in a directory name. The from string is
actually a regular expression; it should always start with `^'.
The function abbreviate-file-name performs these substitutions.
You can set this variable in `site-init.el' to describe the abbreviations appropriate for your site.
Here's an example, from a system on which file system `/home/fsf' and so on are normally accessed through symbolic links named `/fsf' and so on.
(("^/home/fsf" . "/fsf")
("^/home/gp" . "/gp")
("^/home/gd" . "/gd"))
To convert a directory name to its abbreviation, use this function:
directory-abbrev-alist
to its argument, and substitutes `~' for the user's home
directory.
All the directories in the file system form a tree starting at the root directory. A file name can specify all the directory names starting from the root of the tree; then it is called an absolute file name. Or it can specify the position of the file in the tree relative to a default directory; then it is called a relative file name. On Unix, an absolute file name starts with a slash or a tilde (`~'), and a relative one does not. The rules on VMS are complicated.
t if file filename is an absolute
file name, nil otherwise. On VMS, this function understands both
Unix syntax and VMS syntax.
(file-name-absolute-p "~rms/foo")
=> t
(file-name-absolute-p "rms/foo")
=> nil
(file-name-absolute-p "/user/rms/foo")
=> t
Expansion of a file name means converting a relative file name to an absolute one. Since this is done relative to a default directory, you must specify the default directory name as well as the file name to be expanded. Expansion also simplifies file names by eliminating redundancies such as `./' and `name/../'.
default-directory is
used. For example:
(expand-file-name "foo")
=> "/xcssun/users/rms/lewis/foo"
(expand-file-name "../foo")
=> "/xcssun/users/rms/foo"
(expand-file-name "foo" "/usr/spool/")
=> "/usr/spool/foo"
(expand-file-name "$HOME/foo")
=> "/xcssun/users/rms/lewis/$HOME/foo"
Filenames containing `.' or `..' are simplified to their canonical form:
(expand-file-name "bar/../foo")
=> "/xcssun/users/rms/lewis/foo"
Note that expand-file-name does not expand environment
variables; only substitute-in-file-name does that.
On some operating systems, an absolute file name begins with a device
name. On such systems, filename has no relative equivalent based
on directory if they start with two different device names. In
this case, file-relative-name returns filename in absolute
form.
(file-relative-name "/foo/bar" "/foo/")
=> "bar"
(file-relative-name "/foo/bar" "/hack/")
=> "/foo/bar"
expand-file-name uses the default directory when its second
argument is nil.
On Unix systems, the value is always a string ending with a slash.
default-directory
=> "/user/lewis/manual/"
The environment variable name is the series of alphanumeric characters (including underscores) that follow the `$'. If the character following the `$' is a `{', then the variable name is everything up to the matching `}'.
Here we assume that the environment variable HOME, which holds
the user's home directory name, has value `/xcssun/users/rms'.
(substitute-in-file-name "$HOME/foo")
=> "/xcssun/users/rms/foo"
After substitution, if a `~' or a `/' appears following a `/', everything before the following `/' is discarded:
(substitute-in-file-name "bar/~/foo")
=> "~/foo"
(substitute-in-file-name "/usr/local/$HOME/foo")
=> "/xcssun/users/rms/foo"
;; `/usr/local/' has been discarded.
On VMS, `$' substitution is not done, so this function does nothing on VMS except discard superfluous initial components as shown above.
Some programs need to write temporary files. Here is the usual way to construct a name for such a file:
(make-temp-name
(expand-file-name name-of-application
temporary-file-directory))
The job of make-temp-name is to prevent two different users or
two different jobs from trying to use the exact same file name. This
example uses the variable temporary-file-directory to decide
where to put the temporary file. All Emacs Lisp programs should
use temporary-file-directory for this purpose, to give the user
a uniform way to specify the directory for all temporary files.
(make-temp-name "/tmp/foo")
=> "/tmp/foo232J6v"
To prevent conflicts among different libraries running in the same
Emacs, each Lisp program that uses make-temp-name should have its
own string. The number added to the end of string
distinguishes between the same application running in different Emacs
jobs. Additional added characters permit a large number of distinct
names even in one Emacs job.
expand-file-name is a good way to achieve that.
The default value is determined in a reasonable way for your operating
system; on GNU and Unix systems it is based on the TMP and
TMPDIR environment variables.
Even if you do not use make-temp-name to choose the temporary
file's name, you should still use this variable to decide which
directory to put the file in.
This section describes low-level subroutines for completing a file name. For other completion functions, see section Completion.
The argument partial-filename must be a file name containing no directory part and no slash. The current buffer's default directory is prepended to directory, if directory is not absolute.
In the following example, suppose that `~rms/lewis' is the current default directory, and has five files whose names begin with `f': `foo', `file~', `file.c', `file.c.~1~', and `file.c.~2~'.
(file-name-all-completions "f" "")
=> ("foo" "file~" "file.c.~2~"
"file.c.~1~" "file.c")
(file-name-all-completions "fo" "")
=> ("foo")
If only one match exists and filename matches it exactly, the
function returns t. The function returns nil if directory
directory contains no name starting with filename.
In the following example, suppose that the current default directory has five files whose names begin with `f': `foo', `file~', `file.c', `file.c.~1~', and `file.c.~2~'.
(file-name-completion "fi" "")
=> "file"
(file-name-completion "file.c.~1" "")
=> "file.c.~1~"
(file-name-completion "file.c.~1~" "")
=> t
(file-name-completion "file.c.~3" "")
=> nil
file-name-completion usually ignores file names that end in any
string in this list. It does not ignore them when all the possible
completions end in one of these suffixes or when a buffer showing all
possible completions is displayed.
A typical value might look like this:
completion-ignored-extensions
=> (".o" ".elc" "~" ".dvi")
Most of the file names used in Lisp programs are entered by the user.
But occasionally a Lisp program needs to specify a standard file name
for a particular use--typically, to hold customization information
about each user. For example, abbrev definitions are stored (by
default) in the file `~/.abbrev_defs'; the completion
package stores completions in the file `~/.completions'. These are
two of the many standard file names used by parts of Emacs for certain
purposes.
Various operating systems have their own conventions for valid file
names and for which file names to use for user profile data. A Lisp
program which reads a file using a standard file name ought to use, on
each type of system, a file name suitable for that system. The function
convert-standard-filename makes this easy to do.
The recommended way to specify a standard file name in a Lisp program
is to choose a name which fits the conventions of GNU and Unix systems,
usually with a nondirectory part that starts with a period, and pass it
to convert-standard-filename instead of using it directly. Here
is an example from the completion package:
(defvar save-completions-file-name
(convert-standard-filename "~/.completions")
"*The file name to save completions to.")
On GNU and Unix systems, and on some other systems as well,
convert-standard-filename returns its argument unchanged. On
some other systems, it alters the name to fit the system's conventions.
For example, on MS-DOS the alterations made by this function include converting a leading `.' to `_', converting a `_' in the middle of the name to `.' if there is no other `.', inserting a `.' after eight characters if there is none, and truncating to three characters after the `.'. (It makes other changes as well.) Thus, `.abbrev_defs' becomes `_abbrev.def', and `.completions' becomes `_complet.ion'.
A directory is a kind of file that contains other files entered under various names. Directories are a feature of the file system.
Emacs can list the names of the files in a directory as a Lisp list,
or display the names in a buffer using the ls shell command. In
the latter case, it can optionally display information about each file,
depending on the options passed to the ls command.
If full-name is non-nil, the function returns the files'
absolute file names. Otherwise, it returns the names relative to
the specified directory.
If match-regexp is non-nil, this function returns only
those file names that contain a match for that regular expression--the
other file names are excluded from the list.
If nosort is non-nil, directory-files does not sort
the list, so you get the file names in no particular order. Use this if
you want the utmost possible speed and don't care what order the files
are processed in. If the order of processing is visible to the user,
then the user will probably be happier if you do sort the names.
(directory-files "~lewis")
=> ("#foo#" "#foo.el#" "." ".."
"dired-mods.el" "files.texi"
"files.texi.~1~")
An error is signaled if directory is not the name of a directory that can be read.
ls according to
switches. It leaves point after the inserted text.
The argument file may be either a directory name or a file
specification including wildcard characters. If wildcard is
non-nil, that means treat file as a file specification with
wildcards.
If full-directory-p is non-nil, that means the directory
listing is expected to show the full contents of a directory. You
should specify t when file is a directory and switches do
not contain `-d'. (The `-d' option to ls says to
describe a directory itself as a file, rather than showing its
contents.)
This function works by running a directory listing program whose name is
in the variable insert-directory-program. If wildcard is
non-nil, it also runs the shell specified by
shell-file-name, to expand the wildcards.
insert-directory.
Most Emacs Lisp file-manipulation functions get errors when used on
files that are directories. For example, you cannot delete a directory
with delete-file. These special functions exist to create and
delete directories.
delete-file does not work for files that are directories; you
must use delete-directory for them. If the directory contains
any files, delete-directory signals an error.
You can implement special handling for certain file names. This is called making those names magic. The principal use for this feature is in implementing remote file names (see section `Remote Files' in The GNU Emacs Manual).
To define a kind of magic file name, you must supply a regular expression to define the class of names (all those that match the regular expression), plus a handler that implements all the primitive Emacs file operations for file names that do match.
The variable file-name-handler-alist holds a list of handlers,
together with regular expressions that determine when to apply each
handler. Each element has this form:
(regexp . handler)
All the Emacs primitives for file access and file name transformation
check the given file name against file-name-handler-alist. If
the file name matches regexp, the primitives handle that file by
calling handler.
The first argument given to handler is the name of the primitive; the remaining arguments are the arguments that were passed to that operation. (The first of these arguments is typically the file name itself.) For example, if you do this:
(file-exists-p filename)
and filename has handler handler, then handler is called like this:
(funcall handler 'file-exists-p filename)
Here are the operations that a magic file name handler gets to handle:
add-name-to-file, copy-file, delete-directory,
delete-file,
diff-latest-backup-file,
directory-file-name,
directory-files,
dired-call-process,
dired-compress-file, dired-uncache,
expand-file-name,
file-accessible-direc@discretionary{{}{}tory-p},
file-attributes,
file-direct@discretionary{{}{}ory-p},
file-executable-p, file-exists-p,
file-local-copy,
file-modes, file-name-all-completions,
file-name-as-directory,
file-name-completion,
file-name-directory,
file-name-nondirec@discretionary{{}{}tory},
file-name-sans-versions, file-newer-than-file-p,
file-ownership-pre@discretionary{{}{}served-p},
file-readable-p, file-regular-p, file-symlink-p,
file-truename, file-writable-p,
find-backup-file-name,
get-file-buffer,
insert-directory,
insert-file-contents,
load, make-direc@discretionary{{}{}tory},
make-symbolic-link, rename-file, set-file-modes,
set-visited-file-modtime, shell-command,
unhandled-file-name-directory,
vc-regis@discretionary{{}{}tered},
verify-visited-file-modtime,
write-region.
Handlers for insert-file-contents typically need to clear the
buffer's modified flag, with (set-buffer-modified-p nil), if the
visit argument is non-nil. This also has the effect of
unlocking the buffer if it is locked.
The handler function must handle all of the above operations, and possibly others to be added in the future. It need not implement all these operations itself--when it has nothing special to do for a certain operation, it can reinvoke the primitive, to handle the operation "in the usual way". It should always reinvoke the primitive for an operation it does not recognize. Here's one way to do this:
(defun my-file-handler (operation &rest args)
;; First check for the specific operations
;; that we have special handling for.
(cond ((eq operation 'insert-file-contents) ...)
((eq operation 'write-region) ...)
...
;; Handle any operation we don't know about.
(t (let ((inhibit-file-name-handlers
(cons 'my-file-handler
(and (eq inhibit-file-name-operation operation)
inhibit-file-name-handlers)))
(inhibit-file-name-operation operation))
(apply operation args)))))
When a handler function decides to call the ordinary Emacs primitive for
the operation at hand, it needs to prevent the primitive from calling
the same handler once again, thus leading to an infinite recursion. The
example above shows how to do this, with the variables
inhibit-file-name-handlers and
inhibit-file-name-operation. Be careful to use them exactly as
shown above; the details are crucial for proper behavior in the case of
multiple handlers, and for operations that have two file names that may
each have handlers.
nil if there is none. The argument operation should be the
operation to be performed on the file--the value you will pass to the
handler as its first argument when you call it. The operation is needed
for comparison with inhibit-file-name-operation.
If filename specifies a magic file name, which programs outside Emacs cannot directly read or write, this copies the contents to an ordinary file and returns that file's name.
If filename is an ordinary file name, not magic, then this function
does nothing and returns nil.
This is useful for running a subprocess; every subprocess must have a non-magic directory to serve as its current directory, and this function is a good way to come up with one.
The variable format-alist defines a list of file formats,
which describe textual representations used in files for the data (text,
text-properties, and possibly other information) in an Emacs buffer.
Emacs performs format conversion if appropriate when reading and writing
files.
Each format definition is a list of this form:
(name doc-string regexp from-fn to-fn modify mode-fn)
Here is what the elements in a format definition mean:
(position . string), where position is an
integer specifying the relative position in the text to be written, and
string is the annotation to add there. The list must be sorted in
order of position when to-fn returns it.
When write-region actually writes the text from the buffer to the
file, it intermixes the specified annotations at the corresponding
positions. All this takes place without modifying the buffer.
t if the encoding function modifies the buffer, and
nil if it works by returning a list of annotations.
The function insert-file-contents automatically recognizes file
formats when it reads the specified file. It checks the text of the
beginning of the file against the regular expressions of the format
definitions, and if it finds a match, it calls the decoding function for
that format. Then it checks all the known formats over again.
It keeps checking them until none of them is applicable.
Visiting a file, with find-file-noselect or the commands that use
it, performs conversion likewise (because it calls
insert-file-contents); it also calls the mode function for each
format that it decodes. It stores a list of the format names in the
buffer-local variable buffer-file-format.
When write-region writes data into a file, it first calls the
encoding functions for the formats listed in buffer-file-format,
in the order of appearance in the list.
The argument format is a list of format names. If format is
nil, no conversion takes place. Interactively, typing just
RET for format specifies nil.
nil, they specify which part of the file to read, as in
insert-file-contents (see section Reading from Files).
The return value is like what insert-file-contents returns: a
list of the absolute file name and the length of the data inserted
(after conversion).
The argument format is a list of format names. If format is
nil, no conversion takes place. Interactively, typing just
RET for format specifies nil.
buffer-file-format; however, it is used instead of
buffer-file-format for writing auto-save files. This variable is
always buffer-local in all buffers.
Backup files and auto-save files are two methods by which Emacs tries to protect the user from the consequences of crashes or of the user's own errors. Auto-saving preserves the text from earlier in the current editing session; backup files preserve file contents prior to the current session.
A backup file is a copy of the old contents of a file you are editing. Emacs makes a backup file the first time you save a buffer into its visited file. Normally, this means that the backup file contains the contents of the file as it was before the current editing session. The contents of the backup file normally remain unchanged once it exists.
Backups are usually made by renaming the visited file to a new name. Optionally, you can specify that backup files should be made by copying the visited file. This choice makes a difference for files with multiple names; it also can affect whether the edited file remains owned by the original owner or becomes owned by the user editing it.
By default, Emacs makes a single backup file for each file edited. You can alternatively request numbered backups; then each new backup file gets a new name. You can delete old numbered backups when you don't want them any more, or Emacs can delete them automatically.
save-buffer before
saving the buffer the first time.
nil, then
the backup file has been written. Otherwise, the file should be backed
up when it is next saved (if backups are enabled). This is a
permanent local; kill-local-variables does not alter it.
nil, then Emacs creates a backup of each file when it is
saved for the first time--provided that backup-inhibited
is nil (see below).
The following example shows how to change the make-backup-files
variable only in the Rmail buffers and not elsewhere. Setting it
nil stops Emacs from making backups of these files, which may
save disk space. (You would put this code in your `.emacs' file.)
(add-hook 'rmail-mode-hook
(function (lambda ()
(make-local-variable
'make-backup-files)
(setq make-backup-files nil))))
nil, backups are disabled for that file. Otherwise, the other
variables in this section say whether and how to make backups.
The default value is this:
(lambda (name)
(or (< (length name) 5)
(not (string-equal "/tmp/"
(substring name 0 5)))))
nil, backups are inhibited. It records
the result of testing backup-enable-predicate on the visited file
name. It can also coherently be used by other mechanisms that inhibit
backups based on which file is visited. For example, VC sets this
variable non-nil to prevent making backups for files managed
with a version control system.
This is a permanent local, so that changing the major mode does not lose
its value. Major modes should not set this variable--they should set
make-backup-files instead.
There are two ways that Emacs can make a backup file:
The first method, renaming, is the default.
The variable backup-by-copying, if non-nil, says to use
the second method, which is to copy the original file and overwrite it
with the new buffer contents. The variable file-precious-flag,
if non-nil, also has this effect (as a sideline of its main
significance). See section Saving Buffers.
nil, Emacs always makes backup files by
copying.
The following two variables, when non-nil, cause the second
method to be used in certain special cases. They have no effect on the
treatment of files that don't fall into the special cases.
nil, Emacs makes backups by copying for
files with multiple names (hard links).
This variable is significant only if backup-by-copying is
nil, since copying is always used when that variable is
non-nil.
nil, Emacs makes backups by copying in cases
where renaming would change either the owner or the group of the file.
The value has no effect when renaming would not alter the owner or group of the file; that is, for files which are owned by the user and whose group matches the default for a new file created there by the user.
This variable is significant only if backup-by-copying is
nil, since copying is always used when that variable is
non-nil.
If a file's name is `foo', the names of its numbered backup versions are `foo.~v~', for various integers v, like this: `foo.~1~', `foo.~2~', `foo.~3~', ..., `foo.~259~', and so on.
nil
never
The use of numbered backups ultimately leads to a large number of backup versions, which must then be deleted. Emacs can do this automatically or it can ask the user whether to delete them.
If there are backups numbered 1, 2, 3, 5, and 7, and both of these
variables have the value 2, then the backups numbered 1 and 2 are kept
as old versions and those numbered 5 and 7 are kept as new versions;
backup version 3 is excess. The function find-backup-file-name
(see section Naming Backup Files) is responsible for determining which backup
versions to delete, but does not delete them itself.
nil, then saving a file deletes excess
backup versions silently. Otherwise, it asks the user whether to delete
them.
dired-clean-directory). That's the
same thing kept-new-versions specifies when you make a new backup
file. The default value is 2.
The functions in this section are documented mainly because you can customize the naming conventions for backup files by redefining them. If you change one, you probably need to change the rest.
nil value if filename is a
possible name for a backup file. A file with the name filename
need not exist; the function just checks the name.
(backup-file-name-p "foo")
=> nil
(backup-file-name-p "foo~")
=> 3
The standard definition of this function is as follows:
(defun backup-file-name-p (file) "Return non-nil if FILE is a backup file \ name (numeric or not)..." (string-match "~$" file))
Thus, the function returns a non-nil value if the file name ends
with a `~'. (We use a backslash to split the documentation
string's first line into two lines in the text, but produce just one
line in the string itself.)
This simple expression is placed in a separate function to make it easy to redefine for customization.
The standard definition of this function, on most operating systems, is as follows:
(defun make-backup-file-name (file)
"Create the non-numeric backup file name for FILE@enddots{}"
(concat file "~"))
You can change the backup-file naming convention by redefining this
function. The following example redefines make-backup-file-name
to prepend a `.' in addition to appending a tilde:
(defun make-backup-file-name (filename)
(expand-file-name
(concat "." (file-name-nondirectory filename) "~")
(file-name-directory filename)))
(make-backup-file-name "backups.texi")
=> ".backups.texi~"
Some parts of Emacs, including some Dired commands, assume that backup file names end with `~'. If you do not follow that convention, it will not cause serious problems, but these commands may give less-than-desirable results.
find-backup-file-name returns a list whose CAR is
the name for the new backup file and whose CDR is a list of backup
files whose deletion is proposed.
Two variables, kept-old-versions and kept-new-versions,
determine which backup versions should be kept. This function keeps
those versions by excluding them from the CDR of the value.
See section Making and Deleting Numbered Backup Files.
In this example, the value says that `~rms/foo.~5~' is the name to use for the new backup file, and `~rms/foo.~3~' is an "excess" version that the caller should consider deleting now.
(find-backup-file-name "~rms/foo")
=> ("~rms/foo.~5~" "~rms/foo.~3~")
nil if that file has no backup files.
Some file comparison commands use this function so that they can automatically compare a file with its most recent backup.
Emacs periodically saves all files that you are visiting; this is called auto-saving. Auto-saving prevents you from losing more than a limited amount of work if the system crashes. By default, auto-saves happen every 300 keystrokes, or after around 30 seconds of idle time. See section `Auto-Saving: Protection Against Disasters' in The GNU Emacs Manual, for information on auto-save for users. Here we describe the functions used to implement auto-saving and the variables that control them.
nil if the buffer
should not be auto-saved.
buffer-auto-save-file-name => "/xcssun/users/rms/lewis/#files.texi#"
t, a nonempty list, or a positive
integer. Otherwise, it turns auto-saving off.
nil value if filename is a
string that could be the name of an auto-save file. It works based on
knowledge of the naming convention for auto-save files: a name that
begins and ends with hash marks (`#') is a possible auto-save file
name. The argument filename should not contain a directory part.
(make-auto-save-file-name)
=> "/xcssun/users/rms/lewis/#files.texi#"
(auto-save-file-name-p "#files.texi#")
=> 0
(auto-save-file-name-p "files.texi")
=> nil
The standard definition of this function is as follows:
(defun auto-save-file-name-p (filename) "Return non-nil if FILENAME can be yielded by..." (string-match "^#.*#$" filename))
This function exists so that you can customize it if you wish to
change the naming convention for auto-save files. If you redefine it,
be sure to redefine the function make-auto-save-file-name
correspondingly.
auto-save-visited-file-name (described below); you should check
that before calling this function.
(make-auto-save-file-name)
=> "/xcssun/users/rms/lewis/#backup.texi#"
The standard definition of this function is as follows:
(defun make-auto-save-file-name ()
"Return file name to use for auto-saves \
of current buffer@enddots{}"
(if buffer-file-name
(concat
(file-name-directory buffer-file-name)
"#"
(file-name-nondirectory buffer-file-name)
"#")
(expand-file-name
(concat "#%" (buffer-name) "#"))))
This exists as a separate function so that you can redefine it to
customize the naming convention for auto-save files. Be sure to
change auto-save-file-name-p in a corresponding way.
nil, Emacs auto-saves buffers in
the files they are visiting. That is, the auto-save is done in the same
file that you are editing. Normally, this variable is nil, so
auto-save files have distinct names that are created by
make-auto-save-file-name.
When you change the value of this variable, the value does not take
effect until the next time auto-save mode is reenabled in any given
buffer. If auto-save mode is already enabled, auto-saves continue to go
in the same file name until auto-save-mode is called again.
t if the current buffer has been
auto-saved since the last time it was read in or saved.
nil.
nil, buffers that are visiting files
have auto-saving enabled by default. Otherwise, they do not.
Normally, if any buffers are auto-saved, a message that says
`Auto-saving...' is displayed in the echo area while auto-saving is
going on. However, if no-message is non-nil, the message
is inhibited.
If current-only is non-nil, only the current buffer
is auto-saved.
delete-auto-save-files is non-nil. It is called every
time a buffer is saved.
delete-auto-save-file-if-necessary. If it is non-nil,
Emacs deletes auto-save files when a true save is done (in the visited
file). This saves disk space and unclutters your directory.
If it is -1, that means auto-saving is temporarily shut off in this buffer due to a substantial deletion. Explicitly saving the buffer stores a positive value in this variable, thus reenabling auto-saving. Turning auto-save mode off or on also alters this variable.
nil) specifies a file for recording the
names of all the auto-save files. Each time Emacs does auto-saving, it
writes two lines into this file for each buffer that has auto-saving
enabled. The first line gives the name of the visited file (it's empty
if the buffer has none), and the second gives the name of the auto-save
file.
If Emacs exits normally, it deletes this file. If Emacs crashes, you
can look in the file to find all the auto-save files that might contain
work that was otherwise lost. The recover-session command uses
these files.
The default name for this file is in your home directory and starts with `.saves-'. It also contains the Emacs process ID and the host name.
If you have made extensive changes to a file and then change your mind
about them, you can get rid of them by reading in the previous version
of the file with the revert-buffer command. See section `Reverting a Buffer' in The GNU Emacs Manual.
By default, if the latest auto-save file is more recent than the visited
file, revert-buffer asks the user whether to use that instead.
But if the argument ignore-auto is non-nil, then only the
the visited file itself is used. Interactively, ignore-auto is
t unless there is a numeric prefix argument; thus, the
interactive default is to check the auto-save file.
Normally, revert-buffer asks for confirmation before it changes
the buffer; but if the argument noconfirm is non-nil,
revert-buffer does not ask for confirmation.
Reverting tries to preserve marker positions in the buffer by using the
replacement feature of insert-file-contents. If the buffer
contents and the file contents are identical before the revert
operation, reverting preserves all the markers. If they are not
identical, reverting does change the buffer; then it preserves the
markers in the unchanged text (if any) at the beginning and end of the
buffer. Preserving any additional markers would be problematical.
You can customize how revert-buffer does its work by setting
these variables--typically, as buffer-local variables.
revert-buffer
reverts the file without asking the user for confirmation, if the file
has changed on disk and the buffer is not modified.
nil, it is called as a function with no arguments to do
the work of reverting. If the value is nil, reverting works the
usual way.
Modes such as Dired mode, in which the text being edited does not consist of a file's contents but can be regenerated in some other fashion, give this variable a buffer-local value that is a function to regenerate the contents.
nil, is the function to use to
insert the updated contents when reverting this buffer. The function
receives two arguments: first the file name to use; second, t if
the user has asked to read the auto-save file.
revert-buffer before actually
inserting the modified contents--but only if
revert-buffer-function is nil.
Font Lock mode uses this hook to record that the buffer contents are no longer fontified.
revert-buffer after actually inserting
the modified contents--but only if revert-buffer-function is
nil.
Font Lock mode uses this hook to recompute the fonts for the updated buffer contents.
A buffer is a Lisp object containing text to be edited. Buffers are used to hold the contents of files that are being visited; there may also be buffers that are not visiting files. While several buffers may exist at one time, exactly one buffer is designated the current buffer at any time. Most editing commands act on the contents of the current buffer. Each buffer, including the current buffer, may or may not be displayed in any windows.
Buffers in Emacs editing are objects that have distinct names and hold text that can be edited. Buffers appear to Lisp programs as a special data type. You can think of the contents of a buffer as a string that you can extend; insertions and deletions may occur in any part of the buffer. See section Text.
A Lisp buffer object contains numerous pieces of information. Some of this information is directly accessible to the programmer through variables, while other information is accessible only through special-purpose functions. For example, the visited file name is directly accessible through a variable, while the value of point is accessible only through a primitive function.
Buffer-specific information that is directly accessible is stored in
buffer-local variable bindings, which are variable values that are
effective only in a particular buffer. This feature allows each buffer
to override the values of certain variables. Most major modes override
variables such as fill-column or comment-column in this
way. For more information about buffer-local variables and functions
related to them, see section Buffer-Local Variables.
For functions and variables related to visiting files in buffers, see section Visiting Files and section Saving Buffers. For functions and variables related to the display of buffers in windows, see section Buffers and Windows.
t if object is a buffer,
nil otherwise.
There are, in general, many buffers in an Emacs session. At any time, one of them is designated as the current buffer. This is the buffer in which most editing takes place, because most of the primitives for examining or changing text in a buffer operate implicitly on the current buffer (see section Text). Normally the buffer that is displayed on the screen in the selected window is the current buffer, but this is not always so: a Lisp program can temporarily designate any buffer as current in order to operate on its contents, without changing what is displayed on the screen.
The way to designate a current buffer in a Lisp program is by calling
set-buffer. The specified buffer remains current until a new one
is designated.
When an editing command returns to the editor command loop, the
command loop designates the buffer displayed in the selected window as
current, to prevent confusion: the buffer that the cursor is in when
Emacs reads a command is the buffer that the command will apply to.
(See section Command Loop.) Therefore, set-buffer is not the way to
switch visibly to a different buffer so that the user can edit it. For
this, you must use the functions described in section Displaying Buffers in Windows.
However, Lisp functions that change to a different current buffer
should not depend on the command loop to set it back afterwards.
Editing commands written in Emacs Lisp can be called from other programs
as well as from the command loop. It is convenient for the caller if
the subroutine does not change which buffer is current (unless, of
course, that is the subroutine's purpose). Therefore, you should
normally use set-buffer within a save-current-buffer or
save-excursion (see section Excursions) form that will restore the
current buffer when your function is done. Here is an example, the
code for the command append-to-buffer (with the documentation
string abridged):
(defun append-to-buffer (buffer start end)
"Append to specified buffer the text of the region.
..."
(interactive "BAppend to buffer: \nr")
(let ((oldbuf (current-buffer)))
(save-current-buffer
(set-buffer (get-buffer-create buffer))
(insert-buffer-substring oldbuf start end))))
This function binds a local variable to record the current buffer, and
then save-current-buffer arranges to make it current again.
Next, set-buffer makes the specified buffer current. Finally,
insert-buffer-substring copies the string from the original
current buffer to the specified (and now current) buffer.
If the buffer appended to happens to be displayed in some window, the next redisplay will show how its text has changed. Otherwise, you will not see the change immediately on the screen. The buffer becomes current temporarily during the execution of the command, but this does not cause it to be displayed.
If you make local bindings (with let or function arguments) for
a variable that may also have buffer-local bindings, make sure that the
same buffer is current at the beginning and at the end of the local
binding's scope. Otherwise you might bind it in one buffer and unbind
it in another! There are two ways to do this. In simple cases, you may
see that nothing ever changes the current buffer within the scope of the
binding. Otherwise, use save-current-buffer or
save-excursion to make sure that the buffer current at the
beginning is current again whenever the variable is unbound.
It is not reliable to change the current buffer back with
set-buffer, because that won't do the job if a quit happens while
the wrong buffer is current. Here is what not to do:
(let (buffer-read-only
(obuf (current-buffer)))
(set-buffer ...)
...
(set-buffer obuf))
Using save-current-buffer, as shown here, handles quitting,
errors, and throw, as well as ordinary evaluation.
(let (buffer-read-only)
(save-current-buffer
(set-buffer ...)
...))
(current-buffer)
=> #<buffer buffers.texi>
This function returns the buffer identified by buffer-or-name. An error is signaled if buffer-or-name does not identify an existing buffer.
save-current-buffer macro saves the identity of the current
buffer, evaluates the body forms, and finally restores that buffer
as current. The return value is the value of the last form in
body. The current buffer is restored even in case of an abnormal
exit via throw or error (see section Nonlocal Exits).
If the buffer that used to be current has been killed by the time of
exit from save-current-buffer, then it is not made current again,
of course. Instead, whichever buffer was current just before exit
remains current.
with-current-buffer macro saves the identity of the current
buffer, makes buffer current, evaluates the body forms, and
finally restores the buffer. The return value is the value of the last
form in body. The current buffer is restored even in case of an
abnormal exit via throw or error (see section Nonlocal Exits).
with-temp-buffer macro evaluates the body forms
with a temporary buffer as the current buffer. It saves the identity of
the current buffer, creates a temporary buffer and makes it current,
evaluates the body forms, and finally restores the previous
current buffer while killing the temporary buffer.
The return value is the value of the last form in body. You can
return the contents of the temporary buffer by using
(buffer-string) as the last form.
The current buffer is restored even in case of an abnormal exit via
throw or error (see section Nonlocal Exits).
See also with-temp-file in section Writing to Files.
Each buffer has a unique name, which is a string. Many of the functions that work on buffers accept either a buffer or a buffer name as an argument. Any argument called buffer-or-name is of this sort, and an error is signaled if it is neither a string nor a buffer. Any argument called buffer must be an actual buffer object, not a name.
Buffers that are ephemeral and generally uninteresting to the user
have names starting with a space, so that the list-buffers and
buffer-menu commands don't mention them. A name starting with
space also initially disables recording undo information; see
section Undo.
If buffer-name returns nil, it means that buffer
has been killed. See section Killing Buffers.
(buffer-name)
=> "buffers.texi"
(setq foo (get-buffer "temp"))
=> #<buffer temp>
(kill-buffer foo)
=> nil
(buffer-name foo)
=> nil
foo
=> #<killed buffer>
Ordinarily, rename-buffer signals an error if newname is
already in use. However, if unique is non-nil, it modifies
newname to make a name that is not in use. Interactively, you can
make unique non-nil with a numeric prefix argument.
One application of this command is to rename the `*shell*' buffer to some other name, thus making it possible to create a second shell buffer under the name `*shell*'.
nil. If buffer-or-name is a buffer, it
is returned as given. (That is not very useful, so the argument is usually
a name.) For example:
(setq b (get-buffer "lewis"))
=> #<buffer lewis>
(get-buffer b)
=> #<buffer lewis>
(get-buffer "Frazzle-nots")
=> nil
See also the function get-buffer-create in section Creating Buffers.
See the related function generate-new-buffer in section Creating Buffers.
The buffer file name is the name of the file that is visited in
that buffer. When a buffer is not visiting a file, its buffer file name
is nil. Most of the time, the buffer name is the same as the
nondirectory part of the buffer file name, but the buffer file name and
the buffer name are distinct and can be set independently.
See section Visiting Files.
buffer-file-name returns nil. If buffer is not
supplied, it defaults to the current buffer.
(buffer-file-name (other-buffer))
=> "/usr/user/lewis/manual/files.texi"
nil if it is not visiting a file. It
is a permanent local, unaffected by kill-local-variables.
buffer-file-name
=> "/usr/user/lewis/manual/buffers.texi"
It is risky to change this variable's value without doing various other
things. Normally it is better to use set-visited-file-name (see
below); some of the things done there, such as changing the buffer name,
are not strictly necessary, but others are essential to avoid confusing
Emacs.
nil if no file is visited. It is a permanent
local, unaffected by kill-local-variables. See section Truenames.
nil if no
file or a nonexistent file is visited. It is a permanent local,
unaffected by kill-local-variables.
The value is normally a list of the form (filenum
devnum). This pair of numbers uniquely identifies the file among
all files accessible on the system. See the function
file-attributes, in section Other Information about Files, for more information
about them.
nil. The argument
filename, which must be a string, is expanded (see section Functions that Expand Filenames), then compared against the visited file names of all live
buffers.
(get-file-buffer "buffers.texi")
=> #<buffer buffers.texi>
In unusual circumstances, there can be more than one buffer visiting the same file name. In such cases, this function returns the first such buffer in the buffer list.
If filename is nil or the empty string, that stands for
"no visited file". In this case, set-visited-file-name marks
the buffer as having no visited file.
Normally, this function asks the user for confirmation if the specified
file already exists. If no-query is non-nil, that prevents
asking this question.
If along-with-file is non-nil, that means to assume that the
former visited file has been renamed to filename.
When the function set-visited-file-name is called interactively, it
prompts for filename in the minibuffer.
Emacs keeps a flag called the modified flag for each buffer, to
record whether you have changed the text of the buffer. This flag is
set to t whenever you alter the contents of the buffer, and
cleared to nil when you save it. Thus, the flag shows whether
there are unsaved changes. The flag value is normally shown in the mode
line (see section Variables Used in the Mode Line), and controls saving (see section Saving Buffers) and auto-saving (see section Auto-Saving).
Some Lisp programs set the flag explicitly. For example, the function
set-visited-file-name sets the flag to t, because the text
does not match the newly-visited file, even if it is unchanged from the
file formerly visited.
The functions that modify the contents of buffers are described in section Text.
t if the buffer buffer has been modified
since it was last read in from a file or saved, or nil
otherwise. If buffer is not supplied, the current buffer
is tested.
nil, or as unmodified if the flag is nil.
Another effect of calling this function is to cause unconditional
redisplay of the mode line for the current buffer. In fact, the
function force-mode-line-update works by doing this:
(set-buffer-modified-p (buffer-modified-p))
Don't use this function in programs, since it prints a message in the
echo area; use set-buffer-modified-p (above) instead.
nil (or omitted), the current buffer is used.
Suppose that you visit a file and make changes in its buffer, and meanwhile the file itself is changed on disk. At this point, saving the buffer would overwrite the changes in the file. Occasionally this may be what you want, but usually it would lose valuable information. Emacs therefore checks the file's modification time using the functions described below before saving the file.
The function returns t if the last actual modification time and
Emacs's recorded modification time are the same, nil otherwise.
This function is called in set-visited-file-name and other
exceptional places where the usual test to avoid overwriting a changed
file should not be done.
(high . low). (This is the
same format that file-attributes uses to return time values; see
section Other Information about Files.)
nil, and otherwise to the last modification time of the
visited file.
If time is not nil, it should have the form
(high . low) or (high low), in
either case containing two integers, each of which holds 16 bits of the
time.
This function is useful if the buffer was not read from the file normally, or if the file itself has been changed for some known benign reason.
Depending on the user's answer, the function may return normally, in
which case the modification of the buffer proceeds, or it may signal a
file-supersession error with data (filename), in which
case the proposed buffer modification is not allowed.
This function is called automatically by Emacs on the proper occasions. It exists so you can customize Emacs by redefining it. See the file `userlock.el' for the standard definition.
See also the file locking mechanism in section File Locks.
If a buffer is read-only, then you cannot change its contents, although you may change your view of the contents by scrolling and narrowing.
Read-only buffers are used in two kinds of situations:
buffer-read-only to
nil (with let) or bind inhibit-read-only to
t around the places where they themselves change the text.
nil.
nil, then read-only buffers and read-only
characters may be modified. Read-only characters in a buffer are those
that have non-nil read-only properties (either text
properties or overlay properties). See section Properties with Special Meanings, for more
information about text properties. See section Overlays, for more
information about overlays and their properties.
If inhibit-read-only is t, all read-only character
properties have no effect. If inhibit-read-only is a list, then
read-only character properties have no effect if they are members
of the list (comparison is done with eq).
buffer-read-only explicitly to the
proper value, t or nil.
buffer-read-only error if the current
buffer is read-only. See section Interactive Call, for another way to
signal an error if the current buffer is read-only.
The buffer list is a list of all live buffers. Creating a
buffer adds it to this list, and killing a buffer excises it. The order
of the buffers in the list is based primarily on how recently each
buffer has been displayed in the selected window. Buffers move to the
front of the list when they are selected and to the end when they are
buried (see bury-buffer, below). Several functions, notably
other-buffer, use this ordering. A buffer list displayed for the
user also follows this order.
In addition to the fundamental Emacs buffer list, each frame has its
own version of the buffer list, in which the buffers that have been
selected in that frame come first, starting with the buffers most
recently selected in that frame. (This order is recorded in
frame's buffer-list frame parameter; see section Window Frame Parameters.) The buffers that were never selected in frame come
afterward, ordered according to the fundamental Emacs buffer list.
If frame is a frame, this returns frame's buffer list. If
frame is nil, the fundamental Emacs buffer list is used:
all the buffers appear in order of most recent selection, regardless of
which frames they were selected in.
(buffer-list)
=> (#<buffer buffers.texi>
#<buffer *Minibuf-1*> #<buffer buffer.c>
#<buffer *Help*> #<buffer TAGS>)
;; Note that the name of the minibuffer
;; begins with a space!
(mapcar (function buffer-name) (buffer-list))
=> ("buffers.texi" " *Minibuf-1*"
"buffer.c" "*Help*" "TAGS")
The list that buffer-list returns is constructed specifically
by buffer-list; it is not an internal Emacs data structure, and
modifying it has no effect on the order of buffers. If you want to
change the order of buffers in the frame-independent buffer list, here
is an easy way:
(defun reorder-buffer-list (new-list)
(while new-list
(bury-buffer (car new-list))
(setq new-list (cdr new-list))))
With this method, you can specify any order for the list, but there is no danger of losing a buffer or adding something that is not a valid live buffer.
To change the order or value of a frame's buffer list, set the frame's
buffer-list frame parameter with modify-frame-parameters
(see section Access to Frame Parameters).
If buffer is not supplied (or if it is not a buffer), then
other-buffer returns the first buffer in the selected frame's
buffer list that is not now visible in any window in a visible frame.
If frame has a non-nil buffer-predicate parameter,
then other-buffer uses that predicate to decide which buffers to
consider. It calls the predicate once for each buffer, and if the value
is nil, that buffer is ignored. See section Window Frame Parameters.
If visible-ok is nil, other-buffer avoids returning
a buffer visible in any window on any visible frame, except as a last
resort. If visible-ok is non-nil, then it does not matter
whether a buffer is displayed somewhere or not.
If no suitable buffer exists, the buffer `*scratch*' is returned (and created, if necessary).
other-buffer to return.
bury-buffer operates on each frame's buffer-list parameter
as well as the frame-independent Emacs buffer list; therefore, the
buffer that you bury will come last in the value of (buffer-list
frame) and in the value of (buffer-list nil).
If buffer-or-name is nil or omitted, this means to bury the
current buffer. In addition, if the buffer is displayed in the selected
window, this switches to some other buffer (obtained using
other-buffer) in the selected window. But if the buffer is
displayed in some other window, it remains displayed there.
To replace a buffer in all the windows that display it, use
replace-buffer-in-windows. See section Buffers and Windows.
This section describes the two primitives for creating buffers.
get-buffer-create creates a buffer if it finds no existing buffer
with the specified name; generate-new-buffer always creates a new
buffer and gives it a unique name.
Other functions you can use to create buffers include
with-output-to-temp-buffer (see section Temporary Displays) and
create-file-buffer (see section Visiting Files). Starting a
subprocess can also create a buffer (see section Processes).
An error is signaled if name is not a string.
(get-buffer-create "foo")
=> #<buffer foo>
The major mode for the new buffer is set to Fundamental mode. The
variable default-major-mode is handled at a higher level.
See section How Emacs Chooses a Major Mode.
An error is signaled if name is not a string.
(generate-new-buffer "bar")
=> #<buffer bar>
(generate-new-buffer "bar")
=> #<buffer bar<2>>
(generate-new-buffer "bar")
=> #<buffer bar<3>>
The major mode for the new buffer is set to Fundamental mode. The
variable default-major-mode is handled at a higher level.
See section How Emacs Chooses a Major Mode.
See the related function generate-new-buffer-name in section Buffer Names.
Killing a buffer makes its name unknown to Emacs and makes its text space available for other use.
The buffer object for the buffer that has been killed remains in
existence as long as anything refers to it, but it is specially marked
so that you cannot make it current or display it. Killed buffers retain
their identity, however; two distinct buffers, when killed, remain
distinct according to eq.
If you kill a buffer that is current or displayed in a window, Emacs automatically selects or displays some other buffer instead. This means that killing a buffer can in general change the current buffer. Therefore, when you kill a buffer, you should also take the precautions associated with changing the current buffer (unless you happen to know that the buffer being killed isn't current). See section The Current Buffer.
If you kill a buffer that is the base buffer of one or more indirect buffers, the indirect buffers are automatically killed as well.
The buffer-name of a killed buffer is nil. You can use
this feature to test whether a buffer has been killed:
(defun buffer-killed-p (buffer) "Return t if BUFFER is killed." (not (buffer-name buffer)))
nil.
Any processes that have this buffer as the process-buffer are
sent the SIGHUP signal, which normally causes them to terminate.
(The basic meaning of SIGHUP is that a dialup line has been
disconnected.) See section Deleting Processes.
If the buffer is visiting a file and contains unsaved changes,
kill-buffer asks the user to confirm before the buffer is killed.
It does this even if not called interactively. To prevent the request
for confirmation, clear the modified flag before calling
kill-buffer. See section Buffer Modification.
Killing a buffer that is already dead has no effect.
(kill-buffer "foo.unchanged")
=> nil
(kill-buffer "foo.changed")
---------- Buffer: Minibuffer ----------
Buffer foo.changed modified; kill anyway? (yes or no) yes
---------- Buffer: Minibuffer ----------
=> nil
kill-buffer calls the functions
in the list kill-buffer-query-functions, in order of appearance,
with no arguments. The buffer being killed is the current buffer when
they are called. The idea is that these functions ask for confirmation
from the user for various nonstandard reasons. If any of them returns
nil, kill-buffer spares the buffer's life.
kill-buffer after asking all the
questions it is going to ask, just before actually killing the buffer.
The buffer to be killed is current when the hook functions run.
See section Hooks.
nil in a particular buffer, tells
save-buffers-kill-emacs and save-some-buffers to offer to
save that buffer, just as they offer to save file-visiting buffers. The
variable buffer-offer-save automatically becomes buffer-local
when set for any reason. See section Buffer-Local Variables.
An indirect buffer shares the text of some other buffer, which is called the base buffer of the indirect buffer. In some ways it is the analogue, for buffers, of a symbolic link among files. The base buffer may not itself be an indirect buffer.
The text of the indirect buffer is always identical to the text of its base buffer; changes made by editing either one are visible immediately in the other. This includes the text properties as well as the characters themselves.
But in all other respects, the indirect buffer and its base buffer are completely separate. They have different names, different values of point, different narrowing, different markers and overlays (though inserting or deleting text in either buffer relocates the markers and overlays for both), different major modes, and different buffer-local variables.
An indirect buffer cannot visit a file, but its base buffer can. If you try to save the indirect buffer, that actually works by saving the base buffer.
Killing an indirect buffer has no effect on its base buffer. Killing the base buffer effectively kills the indirect buffer in that it cannot ever again be the current buffer.
nil. Otherwise, the value is
another buffer, which is never an indirect buffer.
This chapter describes most of the functions and variables related to Emacs windows. See section Emacs Display, for information on how text is displayed in windows.
A window in Emacs is the physical area of the screen in which a buffer is displayed. The term is also used to refer to a Lisp object that represents that screen area in Emacs Lisp. It should be clear from the context which is meant.
Emacs groups windows into frames. A frame represents an area of screen available for Emacs to use. Each frame always contains at least one window, but you can subdivide it vertically or horizontally into multiple nonoverlapping Emacs windows.
In each frame, at any time, one and only one window is designated as
selected within the frame. The frame's cursor appears in that
window. At any time, one frame is the selected frame; and the window
selected within that frame is the selected window. The selected
window's buffer is usually the current buffer (except when
set-buffer has been used). See section The Current Buffer.
For practical purposes, a window exists only while it is displayed in a frame. Once removed from the frame, the window is effectively deleted and should not be used, even though there may still be references to it from other Lisp objects. Restoring a saved window configuration is the only way for a window no longer on the screen to come back to life. (See section Deleting Windows.)
Each window has the following attributes:
Users create multiple windows so they can look at several buffers at once. Lisp libraries use multiple windows for a variety of reasons, but most often to display related information. In Rmail, for example, you can move through a summary buffer in one window while the other window shows messages one at a time as they are reached.
The meaning of "window" in Emacs is similar to what it means in the context of general-purpose window systems such as X, but not identical. The X Window System places X windows on the screen; Emacs uses one or more X windows as frames, and subdivides them into Emacs windows. When you use Emacs on a character-only terminal, Emacs treats the whole terminal screen as one frame.
Most window systems support arbitrarily located overlapping windows. In contrast, Emacs windows are tiled; they never overlap, and together they fill the whole screen or frame. Because of the way in which Emacs creates new windows and resizes them, not all conceivable tilings of windows on an Emacs frame are actually possible. See section Splitting Windows, and section The Size of a Window.
See section Emacs Display, for information on how the contents of the window's buffer are displayed in the window.
t if object is a window.
The functions described here are the primitives used to split a window
into two windows. Two higher level functions sometimes split a window,
but not always: pop-to-buffer and display-buffer
(see section Displaying Buffers in Windows).
The functions described here do not accept a buffer as an argument. The two "halves" of the split window initially display the same buffer previously visible in the window that was split.
If horizontal is non-nil, then window splits into
two side by side windows. The original window window keeps the
leftmost size columns, and gives the rest of the columns to the
new window. Otherwise, it splits into windows one above the other, and
window keeps the upper size lines and gives the rest of the
lines to the new window. The original window is therefore the
left-hand or upper of the two, and the new window is the right-hand or
lower.
If window is omitted or nil, then the selected window is
split. If size is omitted or nil, then window is
divided evenly into two parts. (If there is an odd line, it is
allocated to the new window.) When split-window is called
interactively, all its arguments are nil.
The following example starts with one window on a screen that is 50 lines high by 80 columns wide; then the window is split.
(setq w (selected-window))
=> #<window 8 on windows.texi>
(window-edges) ; Edges in order:
=> (0 0 80 50) ; left--top--right--bottom
;; Returns window created
(setq w2 (split-window w 15))
=> #<window 28 on windows.texi>
(window-edges w2)
=> (0 15 80 50) ; Bottom window;
; top is line 15
(window-edges w)
=> (0 0 80 15) ; Top window
The screen looks like this:
__________
| | line 0
| w |
|__________|
| | line 15
| w2 |
|__________|
line 50
column 0 column 80
Next, the top window is split horizontally:
(setq w3 (split-window w 35 t))
=> #<window 32 on windows.texi>
(window-edges w3)
=> (35 0 80 15) ; Left edge at column 35
(window-edges w)
=> (0 0 35 15) ; Right edge at column 35
(window-edges w2)
=> (0 15 80 50) ; Bottom window unchanged
Now, the screen looks like this:
column 35
__________
| | | line 0
| w | w3 |
|___|______|
| | line 15
| w2 |
|__________|
line 50
column 0 column 80
Normally, Emacs indicates the border between two side-by-side windows with a scroll bar (see section Window Frame Parameters) or `|' characters. The display table can specify alternative border characters; see section Display Tables.
This function is simply an interface to split-window.
Here is the complete function definition for it:
(defun split-window-vertically (&optional arg) "Split current window into two windows, ..." (interactive "P") (split-window nil (and arg (prefix-numeric-value arg))))
This function is simply an interface to split-window. Here is
the complete definition for split-window-horizontally (except for
part of the documentation string):
(defun split-window-horizontally (&optional arg) "Split selected window into two windows, side by side..." (interactive "P") (split-window nil (and arg (prefix-numeric-value arg)) t))
nil if there is only one window. The
argument no-mini, if non-nil, means don't count the
minibuffer even if it is active; otherwise, the minibuffer window is
included, if active, in the total number of windows, which is compared
against one.
The argument all-frames specifies which frames to consider. Here are the possible values and their meanings:
nil
t
visible
A window remains visible on its frame unless you delete it by calling certain functions that delete windows. A deleted window cannot appear on the screen, but continues to exist as a Lisp object until there are no references to it. There is no way to cancel the deletion of a window aside from restoring a saved window configuration (see section Window Configurations). Restoring a window configuration also deletes any windows that aren't part of that configuration.
When you delete a window, the space it took up is given to one adjacent sibling.
nil if window is deleted, and
t otherwise.
Warning: Erroneous information or fatal errors may result from using a deleted window as if it were live.
nil.
If window is omitted, then the selected window is deleted. An
error is signaled if there is only one window when delete-window
is called.
nil, then the selected window is used by default.
The return value is nil.
delete-windows-on operates frame by frame. If a frame has
several windows showing different buffers, then those showing
buffer are removed, and the others expand to fill the space. If
all windows in some frame are showing buffer (including the case
where there is only one window), then the frame reverts to having a
single window showing another buffer chosen with other-buffer.
See section The Buffer List.
The argument frame controls which frames to operate on. This
function does not use it in quite the same way as the other functions
which scan all windows; specifically, the values t and nil
have the opposite of their meanings in other functions. Here are the
full details:
nil, operate on all frames.
t, operate on the selected frame.
visible, operate on all visible frames.
This function always returns nil.
When a window is selected, the buffer in the window becomes the current buffer, and the cursor will appear in it.
The return value is window.
(setq w (next-window))
(select-window w)
=> #<window 65 on windows.texi>
This macro does not save or restore anything about the sizes, arrangement or contents of windows; therefore, if the forms change them, the change persists.
Each frame, at any time, has a window selected within the frame. This macro saves only the selected window; it does not save anything about other frames. If the forms select some other frame and alter the window selected within it, the change persists.
The following functions choose one of the windows on the screen, offering various criteria for the choice.
The selected window can be the least recently used window if it is the only window. A newly created window becomes the least recently used window until it is selected. A minibuffer window is never a candidate.
The argument frame controls which windows are considered.
nil, consider windows on the selected frame.
t, consider windows on all frames.
visible, consider windows on all visible frames.
If there are two windows of the same size, then the function returns the window that is first in the cyclic ordering of windows (see following section), starting from the selected window.
The argument frame controls which set of windows to
consider. See get-lru-window, above.
When you use the command C-x o (other-window) to select
the next window, it moves through all the windows on the screen in a
specific cyclic order. For any given configuration of windows, this
order never varies. It is called the cyclic ordering of windows.
This ordering generally goes from top to bottom, and from left to right. But it may go down first or go right first, depending on the order in which the windows were split.
If the first split was vertical (into windows one above each other), and then the subwindows were split horizontally, then the ordering is left to right in the top of the frame, and then left to right in the next lower part of the frame, and so on. If the first split was horizontal, the ordering is top to bottom in the left part, and so on. In general, within each set of siblings at any level in the window tree, the order is left to right, or top to bottom.
The value of the argument minibuf determines whether the
minibuffer is included in the window order. Normally, when
minibuf is nil, the minibuffer is included if it is
currently active; this is the behavior of C-x o. (The minibuffer
window is active while the minibuffer is in use. See section Minibuffers.)
If minibuf is t, then the cyclic ordering includes the
minibuffer window even if it is not active.
If minibuf is neither t nor nil, then the minibuffer
window is not included even if it is active.
The argument all-frames specifies which frames to consider. Here are the possible values and their meanings:
nil
t
visible
This example assumes there are two windows, both displaying the buffer `windows.texi':
(selected-window)
=> #<window 56 on windows.texi>
(next-window (selected-window))
=> #<window 52 on windows.texi>
(next-window (next-window (selected-window)))
=> #<window 56 on windows.texi>
next-window.
nil.
In an interactive call, count is the numeric prefix argument.
proc
once for each window with the window as its sole argument.
The optional arguments minibuf and all-frames specify the
set of windows to include in the scan. See next-window, above,
for details.
This section describes low-level functions to examine windows or to display buffers in windows in a precisely controlled fashion. See the following section for related functions that find a window to use and specify a buffer for it. The functions described there are easier to use than these, but they employ heuristics in choosing or creating a window; use these functions when you need complete control.
nil. This is the fundamental primitive
for changing which buffer is displayed in a window, and all ways
of doing that call this function.
(set-window-buffer (selected-window) "foo")
=> nil
(window-buffer)
=> #<buffer windows.texi>
nil if there is none. If there are
several such windows, then the function returns the first one in the
cyclic ordering of windows, starting from the selected window.
See section Cyclic Ordering of Windows.
The argument all-frames controls which windows to consider.
nil, consider windows on the selected frame.
t, consider windows on all frames.
visible, consider windows on all visible frames.
The two optional arguments work like the optional arguments of
next-window (see section Cyclic Ordering of Windows); they are not
like the single optional argument of get-buffer-window. Perhaps
we should change get-buffer-window in the future to make it
compatible with the other functions.
The argument all-frames controls which windows to consider.
nil, consider windows on the selected frame.
t, consider windows on all frames.
visible, consider windows on all visible frames.
set-window-buffer is called, it sets this variable to
(current-time) in the specified buffer (see section Time of Day).
When a buffer is first created, buffer-display-time starts out
with the value nil.
In this section we describe convenient functions that choose a window
automatically and use it to display a specified buffer. These functions
can also split an existing window in certain circumstances. We also
describe variables that parameterize the heuristics used for choosing a
window.
See the preceding section for
low-level functions that give you more precise control. All of these
functions work by calling set-window-buffer.
Do not use the functions in this section in order to make a buffer
current so that a Lisp program can access or modify it; they are too
drastic for that purpose, since they change the display of buffers in
windows, which would be gratuitous and surprise the user. Instead, use
set-buffer and save-current-buffer (see section The Current Buffer), which designate buffers as current for programmed access
without affecting the display of buffers in windows.
set-buffer, which makes buffer-or-name
the current buffer but does not display it in the selected window.
See section The Current Buffer.
If buffer-or-name does not identify an existing buffer, then a new
buffer by that name is created. The major mode for the new buffer is
set according to the variable default-major-mode. See section How Emacs Chooses a Major Mode.
Normally the specified buffer is put at the front of the buffer list
(both the selected frame's buffer list and the frame-independent buffer
list). This affects the operation of other-buffer. However, if
norecord is non-nil, this is not done. See section The Buffer List.
The switch-to-buffer function is often used interactively, as
the binding of C-x b. It is also used frequently in programs. It
always returns nil.
switch-to-buffer.
The currently selected window is absolutely never used to do the job. If it is the only window, then it is split to make a distinct window for this purpose. If the selected window is already displaying the buffer, then it continues to do so, but another window is nonetheless found to display it in as well.
This function updates the buffer list just like switch-to-buffer
unless norecord is non-nil.
If the variable pop-up-frames is non-nil,
pop-to-buffer looks for a window in any visible frame already
displaying the buffer; if there is one, it returns that window and makes
it be selected within its frame. If there is none, it creates a new
frame and displays the buffer in it.
If pop-up-frames is nil, then pop-to-buffer
operates entirely within the selected frame. (If the selected frame has
just a minibuffer, pop-to-buffer operates within the most
recently selected frame that was not just a minibuffer.)
If the variable pop-up-windows is non-nil, windows may
be split to create a new window that is different from the original
window. For details, see section Choosing a Window for Display.
If other-window is non-nil, pop-to-buffer finds or
creates another window even if buffer-or-name is already visible
in the selected window. Thus buffer-or-name could end up
displayed in two windows. On the other hand, if buffer-or-name is
already displayed in the selected window and other-window is
nil, then the selected window is considered sufficient display
for buffer-or-name, so that nothing needs to be done.
All the variables that affect display-buffer affect
pop-to-buffer as well. See section Choosing a Window for Display.
If buffer-or-name is a string that does not name an existing
buffer, a buffer by that name is created. The major mode for the new
buffer is set according to the variable default-major-mode.
See section How Emacs Chooses a Major Mode.
This function updates the buffer list just like switch-to-buffer
unless norecord is non-nil.
other-buffer. In the usual applications of this function, you
don't care which other buffer is used; you just want to make sure that
buffer is no longer displayed.
This function returns nil.
This section describes the basic facility that chooses a window to
display a buffer in---display-buffer. All the higher-level
functions and commands use this subroutine. Here we describe how to use
display-buffer and how to customize it.
pop-to-buffer, but it does not select that window and does not
make the buffer current. The identity of the selected window is
unaltered by this function.
If not-this-window is non-nil, it means to display the
specified buffer in a window other than the selected one, even if it is
already on display in the selected window. This can cause the buffer to
appear in two windows at once. Otherwise, if buffer-or-name is
already being displayed in any window, that is good enough, so this
function does nothing.
display-buffer returns the window chosen to display
buffer-or-name.
If the argument frame is non-nil, it specifies which frames
to check when deciding whether the buffer is already displayed. If the
buffer is already displayed in some window on one of these frames,
display-buffer simply returns that window. Here are the possible
values of frame:
nil, consider windows on the selected frame.
t, consider windows on all frames.
visible, consider windows on all visible frames.
Precisely how display-buffer finds or creates a window depends on
the variables described below.
display-buffer makes new windows.
If it is non-nil and there is only one window, then that window
is split. If it is nil, then display-buffer does not
split the single window, but uses it whole.
display-buffer may split a window,
if there are multiple windows. display-buffer always splits the
largest window if it has at least this many lines. If the largest
window is not this tall, it is split only if it is the sole window and
pop-up-windows is non-nil.
display-buffer makes new frames.
If it is non-nil, display-buffer looks for an existing
window already displaying the desired buffer, on any visible frame. If
it finds one, it returns that window. Otherwise it makes a new frame.
The variables pop-up-windows and split-height-threshold do
not matter if pop-up-frames is non-nil.
If pop-up-frames is nil, then display-buffer either
splits a window or reuses one.
See section Frames, for more information.
pop-up-frames
is non-nil.
Its value should be a function of no arguments. When
display-buffer makes a new frame, it does so by calling that
function, which should return a frame. The default value of the
variable is a function that creates a frame using parameters from
pop-up-frame-alist.
display-buffer makes a new frame. See section Frame Parameters, for
more information about frame parameters.
display-buffer handles the
buffer specially.
By default, special display means to give the buffer a dedicated frame.
If an element is a list, instead of a string, then the CAR of the list is the buffer name, and the rest of the list says how to create the frame. There are two possibilities for the rest of the list. It can be an alist, specifying frame parameters, or it can contain a function and arguments to give to it. (The function's first argument is always the buffer to be displayed; the arguments from the list come after that.)
display-buffer handles the buffer
specially.
By default, special display means to give the buffer a dedicated frame.
If an element is a list, instead of a string, then the CAR of the
list is the regular expression, and the rest of the list says how to
create the frame. See above, under special-display-buffer-names.
The default value of this variable is
special-display-popup-frame.
This function uses an existing window displaying buffer whether or not it is in a frame of its own; but if you set up the above variables in your init file, before buffer was created, then presumably the window was previously made by this function.
special-display-popup-frame to use when it creates a frame.
display-buffer handles the buffer by switching to it in the
selected window.
display-buffer handles the
buffer by switching to it in the selected window.
display-buffer. If it is non-nil, it should be a function
that display-buffer calls to do the work. The function should
accept two arguments, the same two arguments that display-buffer
received. It should choose or create a window, display the specified
buffer, and then return the window.
This hook takes precedence over all the other options and hooks described above.
A window can be marked as "dedicated" to its buffer. Then
display-buffer will not try to use that window to display any
other buffer.
t if window is marked as dedicated;
otherwise nil.
nil, and nondedicated otherwise.
Each window has its own value of point, independent of the value of point in other windows displaying the same buffer. This makes it useful to have multiple windows showing one buffer.
As far as the user is concerned, point is where the cursor is, and when the user switches to another buffer, the cursor jumps to the position of point in that buffer.
When window is the selected window and its buffer is also the current buffer, the value returned is the same as point in that buffer.
Strictly speaking, it would be more correct to return the
"top-level" value of point, outside of any save-excursion
forms. But that value is hard to find.
Each window contains a marker used to keep track of a buffer position that specifies where in the buffer display should start. This position is called the display-start position of the window (or just the start). The character after this position is the one that appears at the upper left corner of the window. It is usually, but not inevitably, at the beginning of a text line.
nil, the selected window is
used. For example,
(window-start)
=> 7058
When you create a window, or display a different buffer in it, the display-start position is set to a display-start position recently used for the same buffer, or 1 if the buffer doesn't have any.
Redisplay updates the window-start position (if you have not specified it explicitly since the previous redisplay) so that point appears on the screen. Nothing except redisplay automatically changes the window-start position; if you move point, do not expect the window-start position to change in response until after the next redisplay.
For a realistic example of using window-start, see the
description of count-lines in section Motion by Text Lines.
nil, the selected window is
used.
Simply changing the buffer text or moving point does not update the
value that window-end returns. The value is updated only when
Emacs redisplays and redisplay completes without being preempted.
If the last redisplay of window was preempted, and did not finish,
Emacs does not know the position of the end of display in that window.
In that case, this function returns nil.
If update is non-nil, window-end always returns
an up-to-date value for where the window ends. If the saved value is
valid, window-end returns that; otherwise it computes the correct
value by scanning the buffer text.
The display routines insist that the position of point be visible when a
buffer is displayed. Normally, they change the display-start position
(that is, scroll the window) whenever necessary to make point visible.
However, if you specify the start position with this function using
nil for noforce, it means you want display to start at
position even if that would put the location of point off the
screen. If this does place point off screen, the display routines move
point to the left margin on the middle line in the window.
For example, if point is 1 and you set the start of the window to 2, then point would be "above" the top of the window. The display routines will automatically move point if it is still 1 when redisplay occurs. Here is an example:
;; Here is what `foo' looks like before executing ;; theset-window-startexpression. ---------- Buffer: foo ---------- -!-This is the contents of buffer foo. 2 3 4 5 6 ---------- Buffer: foo ---------- (set-window-start (selected-window) (1+ (window-start))) => 2 ;; Here is what `foo' looks like after executing ;; theset-window-startexpression. ---------- Buffer: foo ---------- his is the contents of buffer foo. 2 3 -!-4 5 6 ---------- Buffer: foo ----------
If noforce is non-nil, and position would place point
off screen at the next redisplay, then redisplay computes a new window-start
position that works well with point, and thus position is not used.
t if position is within the range
of text currently visible on the screen in window. It returns
nil if position is scrolled vertically out of view. The
argument position defaults to the current position of point;
window, to the selected window. Here is an example:
(or (pos-visible-in-window-p
(point) (selected-window))
(recenter 0))
The pos-visible-in-window-p function considers only vertical
scrolling. If position is out of view only because window
has been scrolled horizontally, pos-visible-in-window-p returns
t. See section Horizontal Scrolling.
Vertical scrolling means moving the text up or down in a window. It
works by changing the value of the window's display-start location. It
may also change the value of window-point to keep it on the
screen.
In the commands scroll-up and scroll-down, the directions
"up" and "down" refer to the motion of the text in the buffer at which
you are looking through the window. Imagine that the text is
written on a long roll of paper and that the scrolling commands move the
paper up and down. Thus, if you are looking at text in the middle of a
buffer and repeatedly call scroll-down, you will eventually see
the beginning of the buffer.
Some people have urged that the opposite convention be used: they imagine that the window moves over text that remains in place. Then "down" commands would take you to the end of the buffer. This view is more consistent with the actual relationship between windows and the text in the buffer, but it is less like what the user sees. The position of a window on the terminal does not move, and short scrolling commands clearly move the text up or down on the screen. We have chosen names that fit the user's point of view.
The scrolling functions (aside from scroll-other-window) have
unpredictable results if the current buffer is different from the buffer
that is displayed in the selected window. See section The Current Buffer.
If count is nil (or omitted), then the length of scroll
is next-screen-context-lines lines less than the usable height of
the window (not counting its mode line).
scroll-up returns nil.
If count is omitted or nil, then the length of the scroll
is next-screen-context-lines lines less than the usable height of
the window (not counting its mode line).
scroll-down returns nil.
nil, are handled
as in scroll-up.
You can specify a buffer to scroll with the variable
other-window-scroll-buffer. When the selected window is the
minibuffer, the next window is normally the one at the top left corner.
You can specify a different window to scroll with the variable
minibuffer-scroll-window. This variable has no effect when any
other window is selected. See section Minibuffer Miscellany.
When the minibuffer is active, it is the next window if the selected
window is the one at the bottom right corner. In this case,
scroll-other-window attempts to scroll the minibuffer. If the
minibuffer contains just one line, it has nowhere to scroll to, so the
line reappears after the echo area momentarily displays the message
"Beginning of buffer".
nil, it tells scroll-other-window
which buffer to scroll.
scroll-conservatively. The
difference is that it if its value is n, that permits scrolling
only by precisely n lines, not a smaller number. This feature
does not work with scroll-margin. The default value is zero.
nil, the scroll functions move point so
that the vertical position of the cursor is unchanged, when that is
possible.
scroll-up
with an argument of nil scrolls so that this many lines at the
bottom of the window appear instead at the top. The default value is
2.
If count is a nonnegative number, it puts the line containing
point count lines down from the top of the window. If count
is a negative number, then it counts upward from the bottom of the
window, so that -1 stands for the last usable line in the window.
If count is a non-nil list, then it stands for the line in
the middle of the window.
If count is nil, recenter puts the line containing
point in the middle of the window, then clears and redisplays the entire
selected frame.
When recenter is called interactively, count is the raw
prefix argument. Thus, typing C-u as the prefix sets the
count to a non-nil list, while typing C-u 4 sets
count to 4, which positions the current line four lines from the
top.
With an argument of zero, recenter positions the current line at
the top of the window. This action is so handy that some people make a
separate key binding to do this. For example,
(defun line-to-top-of-window () "Scroll current line to top of window. Replaces three keystroke sequence C-u 0 C-l." (interactive) (recenter 0)) (global-set-key [kp-multiply] 'line-to-top-of-window)
Because we read English from left to right in the "inner loop", and
from top to bottom in the "outer loop", horizontal scrolling is not
like vertical scrolling. Vertical scrolling involves selection of a
contiguous portion of text to display, but horizontal scrolling causes
part of each line to go off screen. The amount of horizontal scrolling
is therefore specified as a number of columns rather than as a position
in the buffer. It has nothing to do with the display-start position
returned by window-start.
Usually, no horizontal scrolling is in effect; then the leftmost column is at the left edge of the window. In this state, scrolling to the right is meaningless, since there is no data to the left of the screen to be revealed by it; so this is not allowed. Scrolling to the left is allowed; it scrolls the first columns of text off the edge of the window and can reveal additional columns on the right that were truncated before. Once a window has a nonzero amount of leftward horizontal scrolling, you can scroll it back to the right, but only so far as to reduce the net horizontal scroll to zero. There is no limit to how far left you can scroll, but eventually all the text will disappear off the left edge.
window-hscroll (below).
window-hscroll (below).
Once you scroll a window as far right as it can go, back to its normal position where the total leftward scrolling is zero, attempts to scroll any farther right have no effect.
The value is never negative. It is zero when no horizontal scrolling has been done in window (which is usually the case).
If window is nil, the selected window is used.
(window-hscroll)
=> 0
(scroll-left 5)
=> 5
(window-hscroll)
=> 5
The value returned is columns.
(set-window-hscroll (selected-window) 10)
=> 10
Here is how you can determine whether a given position position is off the screen due to horizontal scrolling:
(defun hscroll-on-screen (window position)
(save-excursion
(goto-char position)
(and
(>= (- (current-column) (window-hscroll window)) 0)
(< (- (current-column) (window-hscroll window))
(window-width window)))))
An Emacs window is rectangular, and its size information consists of the height (the number of lines) and the width (the number of character positions in each line). The mode line is included in the height. But the width does not count the scroll bar or the column of `|' characters that separates side-by-side windows.
The following three functions return size information about a window:
frame-height on that frame (since the
last line is always reserved for the minibuffer).
If window is nil, the function uses the selected window.
(window-height)
=> 23
(split-window-vertically)
=> #<window 4 on windows.texi>
(window-height)
=> 11
frame-width on that frame. The width does not include the
window's scroll bar or the column of `|' characters that separates
side-by-side windows.
If window is nil, the function uses the selected window.
(window-width)
=> 80
nil, the selected window is used.
The order of the list is (left top right
bottom), all elements relative to 0, 0 at the top left corner of
the frame. The element right of the value is one more than the
rightmost column used by window, and bottom is one more than
the bottommost row used by window and its mode-line.
When you have side-by-side windows, the right edge value for a window with a neighbor on the right includes the width of the separator between the window and that neighbor. This separator may be a column of `|' characters or it may be a scroll bar. Since the width of the window does not include this separator, the width does not equal the difference between the right and left edges in this case.
Here is the result obtained on a typical 24-line terminal with just one window:
(window-edges (selected-window))
=> (0 0 80 23)
The bottom edge is at line 23 because the last line is the echo area.
If window is at the upper left corner of its frame, then
bottom is the same as the value of (window-height),
right is almost the same as the value of
(window-width)(4), and top and left are zero.
For example, the edges of the following window are `0 0 5 8'.
Assuming that the frame has more than 8 columns, the last column of the
window (column 7) holds a border rather than text. The last row (row 4)
holds the mode line, shown here with `xxxxxxxxx'.
0
_______
0 | |
| |
| |
| |
xxxxxxxxx 4
7
When there are side-by-side windows, any window not at the right edge of its frame has a separator in its last column or columns. The separator counts as one or two columns in the width of the window. A window never includes a separator on its left, since that belongs to the window to the left.
In the following example, let's suppose that the frame is 7 columns wide. Then the edges of the left window are `0 0 4 3' and the edges of the right window are `4 0 7 3'.
___ ___
| | |
| | |
xxxxxxxxx
0 34 7
The window size functions fall into two classes: high-level commands that change the size of windows and low-level functions that access window size. Emacs does not permit overlapping windows or gaps between windows, so resizing one window affects other windows.
window-min-height lines, that window disappears.
If horizontal is non-nil, this function makes
window wider by size columns, stealing columns instead of
lines. If a window from which columns are stolen shrinks below
window-min-width columns, that window disappears.
If the requested size would exceed that of the window's frame, then the function makes the window occupy the entire height (or width) of the frame.
If size is negative, this function shrinks the window by
-size lines or columns. If that makes the window smaller
than the minimum size (window-min-height and
window-min-width), enlarge-window deletes the window.
enlarge-window returns nil.
(defun enlarge-window-horizontally (columns) (enlarge-window columns t))
enlarge-window but negates the argument
size, making the selected window smaller by giving lines (or
columns) to the other windows. If the window shrinks below
window-min-height or window-min-width, then it disappears.
If size is negative, the window is enlarged by -size lines or columns.
(defun shrink-window-horizontally (columns) (shrink-window columns t))
window-min-height lines.
However, the command does nothing if the window is already too small to display the whole text of the buffer, or if part of the contents are currently scrolled off screen, or if the window is not the full width of its frame, or if the window is the only window in its frame.
The following two variables constrain the window-size-changing functions to a minimum height and width.
window-min-height automatically deletes it, and no window may be
created shorter than this. The absolute minimum height is two (allowing
one line for the mode line, and one line for the buffer display).
Actions that change window sizes reset this variable to two if it is
less than two. The default value is 4.
window-min-width automatically deletes it, and no window may be
created narrower than this. The absolute minimum width is one; any
value below that is ignored. The default value is 10.
This section describes how to relate screen coordinates to windows.
window-at returns nil.
If you omit frame, the selected frame is used.
The argument coordinates is a cons cell of the form (x
. y). The coordinates x and y are measured in
characters, and count from the top left corner of the screen or frame.
The value returned by coordinates-in-window-p is non-nil
if the coordinates are inside window. The value also indicates
what part of the window the position is in, as follows:
(relx . rely)
mode-line
vertical-split
nil
The function coordinates-in-window-p does not require a frame as
argument because it always uses the frame that window is on.
A window configuration records the entire layout of one frame--all windows, their sizes, which buffers they contain, what part of each buffer is displayed, and the values of point and the mark. You can bring back an entire previous layout by restoring a window configuration previously saved.
If you want to record all frames instead of just one, use a frame configuration instead of a window configuration. See section Frame Configurations.
window-min-height, window-min-width and
minibuffer-scroll-window. An exception is made for point in the
current buffer, whose value is not saved.
current-window-configuration. This configuration is restored in
the frame from which configuration was made, whether that frame is
selected or not. This always counts as a window size change and
triggers execution of the window-size-change-functions
(see section Hooks for Window Scrolling and Changes), because set-window-configuration doesn't
know how to tell whether the new configuration actually differs from the
old one.
If the frame which configuration was saved from is dead, all this
function does is restore the three variables window-min-height,
window-min-width and minibuffer-scroll-window.
Here is a way of using this function to get the same effect
as save-window-excursion:
(let ((config (current-window-configuration)))
(unwind-protect
(progn (split-window-vertically nil)
...)
(set-window-configuration config)))
save-excursion also, if you wish to preserve that.
Don't use this construct when save-selected-window is all you need.
Exit from save-window-excursion always triggers execution of the
window-size-change-functions. (It doesn't know how to tell
whether the restored configuration actually differs from the one in
effect at the end of the forms.)
The return value is the value of the final form in forms. For example:
(split-window)
=> #<window 25 on control.texi>
(setq w (selected-window))
=> #<window 19 on control.texi>
(save-window-excursion
(delete-other-windows w)
(switch-to-buffer "foo")
'do-something)
=> do-something
;; The screen is now split again.
t if object is a window configuration.
t even if those
aspects differ.
The function equal can also compare two window configurations; it
regards configurations as unequal if they differ in any respect, even a
saved point or mark.
Primitives to look inside of window configurations would make sense, but none are implemented. It is not clear they are useful enough to be worth implementing.
This section describes how a Lisp program can take action whenever a
window displays a different part of its buffer or a different buffer.
There are three actions that can change this: scrolling the window,
switching buffers in the window, and changing the size of the window.
The first two actions run window-scroll-functions; the last runs
window-size-change-functions. The paradigmatic use of these
hooks is in the implementation of Lazy Lock mode; see section `Font Lock Support Modes' in The GNU Emacs Manual.
Displaying a different buffer in the window also runs these functions.
These functions must be careful in using window-end
(see section The Window Start Position); if you need an up-to-date value, you must use
the update argument to ensure you get it.
Each function receives the frame as its sole argument. There is no direct way to find out which windows on that frame have changed size, or precisely how. However, if a size-change function records, at each call, the existing windows and their sizes, it can also compare the present sizes and the previous sizes.
Creating or deleting windows counts as a size change, and therefore causes these functions to be called. Changing the frame size also counts, because it changes the sizes of the existing windows.
It is not a good idea to use save-window-excursion (see section Window Configurations) in these functions, because that always counts as a
size change, and it would cause these functions to be called over and
over. In most cases, save-selected-window (see section Selecting Windows) is what you need here.
set-window-redisplay-end-trigger. The
functions are called with two arguments: the window, and the end trigger
position. Storing nil for the end trigger position turns off the
feature, and the trigger value is automatically reset to nil just
after the hook is run.
A frame is a rectangle on the screen that contains one or more Emacs windows. A frame initially contains a single main window (plus perhaps a minibuffer window), which you can subdivide vertically or horizontally into smaller windows.
When Emacs runs on a text-only terminal, it starts with one terminal frame. If you create additional ones, Emacs displays one and only one at any given time--on the terminal screen, of course.
When Emacs communicates directly with a supported window system, such as X Windows, it does not have a terminal frame; instead, it starts with a single window frame, but you can create more, and Emacs can display several such frames at once as is usual for window systems.
t if object is a frame, and
nil otherwise.
See section Emacs Display, for information about the related topic of controlling Emacs redisplay.
To create a new frame, call the function make-frame.
The argument is an alist specifying frame parameters. Any parameters
not mentioned in alist default according to the value of the
variable default-frame-alist; parameters not specified even there
default from the standard X resources or whatever is used instead on
your system.
The set of possible parameters depends in principle on what kind of window system Emacs uses to display its frames. See section Window Frame Parameters, for documentation of individual parameters you can specify.
make-frame before it actually creates the
frame.
make-frame after it creates the frame.
Each function in after-make-frame-hook receives one argument, the
frame just created.
A single Emacs can talk to more than one X display.
Initially, Emacs uses just one display--the one chosen with the
DISPLAY environment variable or with the `--display' option
(see section `Initial Options' in The GNU Emacs Manual). To connect to
another display, use the command make-frame-on-display or specify
the display frame parameter when you create the frame.
Emacs treats each X server as a separate terminal, giving each one its own selected frame and its own minibuffer windows.
A few Lisp variables are terminal-local; that is, they have a
separate binding for each terminal. The binding in effect at any time
is the one for the terminal that the currently selected frame belongs
to. These variables include default-minibuffer-frame,
defining-kbd-macro, last-kbd-macro, and
system-key-alist. They are always terminal-local, and can never
be buffer-local (see section Buffer-Local Variables) or frame-local.
A single X server can handle more than one screen. A display name `host:server.screen' has three parts; the last part specifies the screen number for a given server. When you use two screens belonging to one server, Emacs knows by the similarity in their names that they share a single keyboard, and it treats them as a single terminal.
make-frame (see section Creating Frames).
The optional argument xrm-string, if not nil, is a
string of resource names and values, in the same format used in the
`.Xresources' file. The values you specify override the resource
values recorded in the X server itself; they apply to all Emacs frames
created on this display. Here's an example of what this string might
look like:
"*BorderWidth: 3\n*InternalBorder: 2\n"
See section X Resources.
A frame has many parameters that control its appearance and behavior. Just what parameters a frame has depends on what display mechanism it uses.
Frame parameters exist for the sake of window systems. A terminal frame
has a few parameters, mostly for compatibility's sake; only the height,
width, name, title, buffer-list and
buffer-predicate parameters do something special.
These functions let you read and change the parameter values of a frame.
frame-parameters returns an alist listing all the
parameters of frame and their values.
(parm . value), where parm is a symbol naming a
parameter. If you don't mention a parameter in alist, its value
doesn't change.
You can specify the parameters for the initial startup frame
by setting initial-frame-alist in your `.emacs' file.
(parameter . value)
Emacs creates the initial frame before it reads your `~/.emacs'
file. After reading that file, Emacs checks initial-frame-alist,
and applies the parameter settings in the altered value to the already
created initial frame.
If these settings affect the frame geometry and appearance, you'll see the frame appear with the wrong ones and then change to the specified ones. If that bothers you, you can specify the same geometry and appearance with X resources; those do take affect before the frame is created. See section `X Resources' in The GNU Emacs Manual.
X resource settings typically apply to all frames. If you want to
specify some X resources solely for the sake of the initial frame, and
you don't want them to apply to subsequent frames, here's how to achieve
this. Specify parameters in default-frame-alist to override the
X resources for subsequent frames; then, to prevent these from affecting
the initial frame, specify the same parameters in
initial-frame-alist with values that match the X resources.
If these parameters specify a separate minibuffer-only frame with
(minibuffer . nil), and you have not created one, Emacs creates
one for you.
See also special-display-frame-alist, in section Choosing a Window for Display.
If you use options that specify window appearance when you invoke Emacs,
they take effect by adding elements to default-frame-alist. One
exception is `-geometry', which adds the specified position to
initial-frame-alist instead. See section `Command Arguments' in The GNU Emacs Manual.
Just what parameters a frame has depends on what display mechanism it
uses. Here is a table of the parameters that have special meanings in a
window frame; of these, name, title, height,
width, buffer-list and buffer-predicate provide
meaningful information in terminal frames.
display
"host:dpy.screen", just like the
DISPLAY environment variable.
title
nil title, it appears in the window system's
border for the frame, and also in the mode line of windows in that frame
if mode-line-frame-identification uses `%F'
(see section %-Constructs in the Mode Line). This is normally the case when Emacs is not
using a window system, and can only display one frame at a time.
See section Frame Titles.
name
title parameter is unspecified or nil. If
you don't specify a name, Emacs sets the frame name automatically
(see section Frame Titles).
If you specify the frame name explicitly when you create the frame, the
name is also used (instead of the name of the Emacs executable) when
looking up X resources for the frame.
left
(+ pos) which permits specifying a
negative pos value.
A negative number -pos, or a list of the form (-
pos), actually specifies the position of the right edge of the
window with respect to the right edge of the screen. A positive value
of pos counts toward the left. Reminder: if the
parameter is a negative integer -pos, then pos is
positive.
Some window managers ignore program-specified positions. If you want to
be sure the position you specify is not ignored, specify a
non-nil value for the user-position parameter as well.
top
(+ pos) which permits specifying a
negative pos value.
A negative number -pos, or a list of the form (-
pos), actually specifies the position of the bottom edge of the
window with respect to the bottom edge of the screen. A positive value
of pos counts toward the top. Reminder: if the
parameter is a negative integer -pos, then pos is
positive.
Some window managers ignore program-specified positions. If you want to
be sure the position you specify is not ignored, specify a
non-nil value for the user-position parameter as well.
icon-left
icon-top
user-position
left and top parameters, use this parameter to say whether
the specified position was user-specified (explicitly requested in some
way by a human user) or merely program-specified (chosen by a program).
A non-nil value says the position was user-specified.
Window managers generally heed user-specified positions, and some heed
program-specified positions too. But many ignore program-specified
positions, placing the window in a default fashion or letting the user
place it with the mouse. Some window managers, including twm,
let the user specify whether to obey program-specified positions or
ignore them.
When you call make-frame, you should specify a non-nil
value for this parameter if the values of the left and top
parameters represent the user's stated preference; otherwise, use
nil.
height
frame-pixel-height; see section Frame Size And Position.)
width
frame-pixel-width; see section Frame Size And Position.)
window-id
minibuffer
t means
yes, nil means no, only means this frame is just a
minibuffer. If the value is a minibuffer window (in some other frame),
the new frame uses that minibuffer.
buffer-predicate
other-buffer uses this predicate (from the selected frame) to
decide which buffers it should consider, if the predicate is not
nil. It calls the predicate with one argument, a buffer, once for
each buffer; if the predicate returns a non-nil value, it
considers that buffer.
buffer-list
font
auto-raise
nil means yes).
auto-lower
nil means yes).
vertical-scroll-bars
left,
right, and nil for no scroll bars.
horizontal-scroll-bars
nil means yes). (Horizontal scroll bars are not currently
implemented.)
scroll-bar-width
icon-type
nil value specifies the default bitmap icon (a
picture of a gnu); nil specifies a text icon.
icon-name
nil, the frame's title is used.
foreground-color
foreground-color frame parameter, you should
call frame-update-face-colors to update faces accordingly.
background-color
background-color frame parameter, you should
call frame-update-face-colors to update faces accordingly.
See section Functions for Working with Faces.
background-mode
dark or light, according
to whether the background color is a light one or a dark one.
mouse-color
cursor-color
border-color
display-type
color, grayscale or
mono.
cursor-type
bar,
box, and (bar . width). The symbol box
specifies an ordinary black box overlaying the character after point;
that is the default. The symbol bar specifies a vertical bar
between characters as the cursor. (bar . width) specifies
a bar width pixels wide.
border-width
internal-border-width
unsplittable
nil, this frame's window is never split automatically.
visibility
nil for invisible, t for visible, and icon for
iconified. See section Visibility of Frames.
menu-bar-lines
You can read or change the size and position of a frame using the
frame parameters left, top, height, and
width. Whatever geometry parameters you don't specify are chosen
by the window manager in its usual fashion.
Here are some special features for working with sizes and positions:
Negative parameter values position the bottom edge of the window up from the bottom edge of the screen, or the right window edge to the left of the right edge of the screen. It would probably be better if the values were always counted from the left and top, so that negative arguments would position the frame partly off the top or left edge of the screen, but it seems inadvisable to change that now.
frame-height and
frame-width. When you are using a non-window terminal, the size
of the frame is normally the same as the size of the terminal screen.
To set the size based on values measured in pixels, use
frame-char-height and frame-char-width to convert
them to units of characters.
If pretend is non-nil, then Emacs displays lines
lines of output in frame, but does not change its value for the
actual height of the frame. This is only useful for a terminal frame.
Using a smaller height than the terminal actually implements may be
useful to reproduce behavior observed on a smaller screen, or if the
terminal malfunctions when using its whole screen. Setting the frame
height "for real" does not always work, because knowing the correct
actual size may be necessary for correct cursor positioning on a
terminal frame.
set-frame-height.
The older functions set-screen-height and
set-screen-width were used to specify the height and width of the
screen, in Emacs versions that did not support multiple frames. They
are semi-obsolete, but still work; they apply to the selected frame.
x-parse-geometry converts a standard X window
geometry string to an alist that you can use as part of the argument to
make-frame.
The alist describes which parameters were specified in geom, and
gives the values specified for them. Each element looks like
(parameter . value). The possible parameter
values are left, top, width, and height.
For the size parameters, the value must be an integer. The position
parameter names left and top are not totally accurate,
because some values indicate the position of the right or bottom edges
instead. These are the value possibilities for the position
parameters:
(+ position)
(- position)
Here is an example:
(x-parse-geometry "35x70+0-0")
=> ((height . 70) (width . 35)
(top - 0) (left . 0))
Every frame has a name parameter; this serves as the default
for the frame title which window systems typically display at the top of
the frame. You can specify a name explicitly by setting the name
frame property.
Normally you don't specify the name explicitly, and Emacs computes the
frame name automatically based on a template stored in the variable
frame-title-format. Emacs recomputes the name each time the
frame is redisplayed.
mode-line-format. See section The Data Structure of the Mode Line.
t when
there are two or more frames (not counting minibuffer-only frames or
invisible frames). The default value of frame-title-format uses
multiple-frames so as to put the buffer name in the frame title
only when there is more than one frame.
Frames remain potentially visible until you explicitly delete them. A deleted frame cannot appear on the screen, but continues to exist as a Lisp object until there are no references to it. There is no way to cancel the deletion of a frame aside from restoring a saved frame configuration (see section Frame Configurations); this is similar to the way windows behave.
frame-live-p returns non-nil if the frame
frame has not been deleted.
Some window managers provide a command to delete a window. These work
by sending a special message to the program that operates the window.
When Emacs gets one of these commands, it generates a
delete-frame event, whose normal definition is a command that
calls the function delete-frame. See section Miscellaneous Window System Events.
frame-list returns a list of all the frames that
have not been deleted. It is analogous to buffer-list for
buffers. The list that you get is newly created, so modifying the list
doesn't have any effect on the internals of Emacs.
next-frame lets you cycle conveniently through all
the frames from an arbitrary starting point. It returns the "next"
frame after frame in the cycle. If frame is omitted or
nil, it defaults to the selected frame.
The second argument, minibuf, says which frames to consider:
nil
visible
next-frame, but cycles through all frames in the opposite
direction.
See also next-window and previous-window, in section Cyclic Ordering of Windows.
Each window is part of one and only one frame; you can get the frame
with window-frame.
All the non-minibuffer windows in a frame are arranged in a cyclic order. The order runs from the frame's top window, which is at the upper left corner, down and to the right, until it reaches the window at the lower right corner (always the minibuffer window, if the frame has one), and then it moves back to the top. See section Cyclic Ordering of Windows.
At any time, exactly one window on any frame is selected within the
frame. The significance of this designation is that selecting the
frame also selects this window. You can get the frame's current
selected window with frame-selected-window.
Conversely, selecting a window for Emacs with select-window also
makes that window selected within its frame. See section Selecting Windows.
Another function that (usually) returns one of the windows in a given
frame is minibuffer-window. See section Minibuffer Miscellany.
Normally, each frame has its own minibuffer window at the bottom, which
is used whenever that frame is selected. If the frame has a minibuffer,
you can get it with minibuffer-window (see section Minibuffer Miscellany).
However, you can also create a frame with no minibuffer. Such a frame
must use the minibuffer window of some other frame. When you create the
frame, you can specify explicitly the minibuffer window to use (in some
other frame). If you don't, then the minibuffer is found in the frame
which is the value of the variable default-minibuffer-frame. Its
value should be a frame that does have a minibuffer.
If you use a minibuffer-only frame, you might want that frame to raise
when you enter the minibuffer. If so, set the variable
minibuffer-auto-raise to t. See section Raising and Lowering Frames.
At any time, one frame in Emacs is the selected frame. The selected window always resides on the selected frame.
Some window systems and window managers direct keyboard input to the window object that the mouse is in; others require explicit clicks or commands to shift the focus to various window objects. Either way, Emacs automatically keeps track of which frame has the focus.
Lisp programs can also switch frames "temporarily" by calling the
function select-frame. This does not alter the window system's
concept of focus; rather, it escapes from the window manager's control
until that control is somehow reasserted.
When using a text-only terminal, only the selected terminal frame is
actually displayed on the terminal. switch-frame is the only way
to switch frames, and the change lasts until overridden by a subsequent
call to switch-frame. Each terminal screen except for the
initial one has a number, and the number of the selected frame appears
in the mode line before the buffer name (see section Variables Used in the Mode Line).
Emacs cooperates with the window system by arranging to select frames as
the server and window manager request. It does so by generating a
special kind of input event, called a focus event, when
appropriate. The command loop handles a focus event by calling
handle-switch-frame. See section Focus Events.
Focus events normally do their job by invoking this command. Don't call it for any other reason.
last-event-frame will be focus-frame. Also, switch-frame
events specifying frame will instead select focus-frame.
If focus-frame is nil, that cancels any existing
redirection for frame, which therefore once again receives its own
events.
One use of focus redirection is for frames that don't have minibuffers. These frames use minibuffers on other frames. Activating a minibuffer on another frame redirects focus to that frame. This puts the focus on the minibuffer's frame, where it belongs, even though the mouse remains in the frame that activated the minibuffer.
Selecting a frame can also change focus redirections. Selecting frame
bar, when foo had been selected, changes any redirections
pointing to foo so that they point to bar instead. This
allows focus redirection to work properly when the user switches from
one frame to another using select-window.
This means that a frame whose focus is redirected to itself is treated
differently from a frame whose focus is not redirected.
select-frame affects the former but not the latter.
The redirection lasts until redirect-frame-focus is called to
change it.
nil says that it does.
When this is so, the command other-frame moves the mouse to a
position consistent with the new selected frame.
A window frame may be visible, invisible, or iconified. If it is visible, you can see its contents. If it is iconified, the frame's contents do not appear on the screen, but an icon does. If the frame is invisible, it doesn't show on the screen, not even as an icon.
Visibility is meaningless for terminal frames, since only the selected one is actually displayed in any case.
t if frame is visible, nil if it is invisible, and
icon if it is iconified.
The visibility status of a frame is also available as a frame parameter. You can read or change it as such. See section Window Frame Parameters.
The user can iconify and deiconify frames with the window manager. This happens below the level at which Emacs can exert any control, but Emacs does provide events that you can use to keep track of such changes. See section Miscellaneous Window System Events.
Most window systems use a desktop metaphor. Part of this metaphor is the idea that windows are stacked in a notional third dimension perpendicular to the screen surface, and thus ordered from "highest" to "lowest". Where two windows overlap, the one higher up covers the one underneath. Even a window at the bottom of the stack can be seen if no other window overlaps it.
A window's place in this ordering is not fixed; in fact, users tend to change the order frequently. Raising a window means moving it "up", to the top of the stack. Lowering a window means moving it to the bottom of the stack. This motion is in the notional third dimension only, and does not change the position of the window on the screen.
You can raise and lower Emacs frame Windows with these functions:
nil, activation of the minibuffer raises the frame
that the minibuffer window is in.
You can also enable auto-raise (raising automatically when a frame is selected) or auto-lower (lowering automatically when it is deselected) for any frame using frame parameters. See section Window Frame Parameters.
A frame configuration records the current arrangement of frames, all their properties, and the window configuration of each one. (See section Window Configurations.)
Sometimes it is useful to track the mouse, which means to display something to indicate where the mouse is and move the indicator as the mouse moves. For efficient mouse tracking, you need a way to wait until the mouse actually moves.
The convenient way to track the mouse is to ask for events to represent mouse motion. Then you can wait for motion by waiting for an event. In addition, you can easily handle any other sorts of events that may occur. That is useful, because normally you don't want to track the mouse forever--only until some other event, such as the release of a button.
read-event to
read the motion events and modify the display accordingly. See section Motion Events, for the format of mouse motion events.
The value of track-mouse is that of the last form in body.
You should design body to return when it sees the up-event that
indicates the release of the button, or whatever kind of event means
it is time to stop tracking.
The usual purpose of tracking mouse motion is to indicate on the screen the consequences of pushing or releasing a button at the current position.
In many cases, you can avoid the need to track the mouse by using
the mouse-face text property (see section Properties with Special Meanings).
That works at a much lower level and runs more smoothly than
Lisp-level mouse tracking.
The functions mouse-position and set-mouse-position
give access to the current position of the mouse.
(frame x . y), where x
and y are integers giving the position in characters relative to
the top left corner of the inside of frame.
mouse-position except that it returns
coordinates in units of pixels rather than units of characters.
set-mouse-position except that
x and y are in units of pixels rather than units of
characters. These coordinates are not required to be within the frame.
If frame is not visible, this function does nothing. The return value is not significant.
When using a window system, a Lisp program can pop up a menu so that the user can choose an alternative with the mouse.
The argument position specifies where on the screen to put the menu. It can be either a mouse button event (which says to put the menu where the user actuated the button) or a list of this form:
((xoffset yoffset) window)
where xoffset and yoffset are coordinates, measured in pixels, counting from the top left corner of window's frame.
If position is t, it means to use the current mouse
position. If position is nil, it means to precompute the
key binding equivalents for the keymaps specified in menu,
without actually displaying or popping up the menu.
The argument menu says what to display in the menu. It can be a keymap or a list of keymaps (see section Menu Keymaps). Alternatively, it can have the following form:
(title pane1 pane2...)
where each pane is a list of form
(title (line . item)...)
Each line should be a string, and each item should be the value to return if that line is chosen.
Usage note: Don't use x-popup-menu to display a menu
if you could do the job with a prefix key defined with a menu keymap.
If you use a menu keymap to implement a menu, C-h c and C-h
a can see the individual items in that menu and provide help for them.
If instead you implement the menu by defining a command that calls
x-popup-menu, the help facilities cannot know what happens inside
that command, so they cannot give any help for the menu's items.
The menu bar mechanism, which lets you switch between submenus by
moving the mouse, cannot look within the definition of a command to see
that it calls x-popup-menu. Therefore, if you try to implement a
submenu using x-popup-menu, it cannot work with the menu bar in
an integrated fashion. This is why all menu bar submenus are
implemented with menu keymaps within the parent menu, and never with
x-popup-menu. See section The Menu Bar,
If you want a menu bar submenu to have contents that vary, you should
still use a menu keymap to implement it. To make the contents vary, add
a hook function to menu-bar-update-hook to update the contents of
the menu keymap as necessary.
A dialog box is a variant of a pop-up menu--it looks a little
different, it always appears in the center of a frame, and it has just
one level and one pane. The main use of dialog boxes is for asking
questions that the user can answer with "yes", "no", and a few other
alternatives. The functions y-or-n-p and yes-or-no-p use
dialog boxes instead of the keyboard, when called from commands invoked
by mouse clicks.
(title (string . value)...)
which looks like the list that specifies a single pane for
x-popup-menu.
The return value is value from the chosen alternative.
An element of the list may be just a string instead of a cons cell
(string . value). That makes a box that cannot
be selected.
If nil appears in the list, it separates the left-hand items from
the right-hand items; items that precede the nil appear on the
left, and items that follow the nil appear on the right. If you
don't include a nil in the list, then approximately half the
items appear on each side.
Dialog boxes always appear in the center of a frame; the argument
position specifies which frame. The possible values are as in
x-popup-menu, but the precise coordinates don't matter; only the
frame matters.
In some configurations, Emacs cannot display a real dialog box; so instead it displays the same items in a pop-up menu in the center of the frame.
These variables specify which shape to use for the mouse pointer in various situations, when using the X Window System:
x-pointer-shape
x-sensitive-text-pointer-shape
These variables affect newly created frames. They do not normally affect existing frames; however, if you set the mouse color of a frame, that also updates its pointer shapes based on the current values of these variables. See section Window Frame Parameters.
The values you can use, to specify either of these pointer shapes, are defined in the file `lisp/term/x-win.el'. Use M-x apropos RET x-pointer RET to see a list of them.
The X server records a set of selections which permit transfer of data between application programs. The various selections are distinguished by selection types, represented in Emacs by symbols. X clients including Emacs can read or set the selection for any given type.
nil, it means to clear out the
selection. Otherwise, data may be a string, a symbol, an integer
(or a cons of two integers or list of two integers), an overlay, or a
cons of two markers pointing to the same buffer. An overlay or a pair
of markers stands for text in the overlay or between the markers.
The argument data may also be a vector of valid non-vector selection values.
Each possible type has its own selection value, which changes
independently. The usual values of type are PRIMARY and
SECONDARY; these are symbols with upper-case names, in accord
with X Window System conventions. The default is PRIMARY.
PRIMARY.
The data-type argument specifies the form of data conversion to
use, to convert the raw data obtained from another X client into Lisp
data. Meaningful values include TEXT, STRING,
TARGETS, LENGTH, DELETE, FILE_NAME,
CHARACTER_POSITION, LINE_NUMBER, COLUMN_NUMBER,
OWNER_OS, HOST_NAME, USER, CLASS,
NAME, ATOM, and INTEGER. (These are symbols with
upper-case names in accord with X conventions.) The default for
data-type is STRING.
The X server also has a set of numbered cut buffers which can store text or other data being moved between applications. Cut buffers are considered obsolete, but Emacs supports them for the sake of X clients that still use them.
compound-text.
The argument pattern should be a string, perhaps with wildcard characters: the `*' character matches any substring, and the `?' character matches any single character. Pattern matching of font names ignores case.
If you specify face and frame, face should be a face name (a symbol) and frame should be a frame.
The optional argument maximum sets a limit on how many fonts to
return. If this is non-nil, then the return value is truncated
after the first maximum matching fonts. Specifying a small value
for maximum can make this function much faster, in cases where
many fonts match the pattern.
A fontset is a list of fonts, each assigned to a range of character codes. An individual font cannot display the whole range of characters that Emacs supports, but a fontset can. Fontsets have names, just as fonts do, and you can use a fontset name in place of a font name when you specify the "font" for a frame or a face. Here is information about defining a fontset under Lisp program control.
fontpattern, [charsetname:fontname]...
Whitespace characters before and after the commas are ignored.
The first part of the string, fontpattern, should have the form of a standard X font name, except that the last two fields should be `fontset-alias'.
The new fontset has two names, one long and one short. The long name is
fontpattern in its entirety. The short name is
`fontset-alias'. You can refer to the fontset by either
name. If a fontset with the same name already exists, an error is
signaled, unless noerror is non-nil, in which case this
function does nothing.
If optional argument style-variant-p is non-nil, that says
to create bold, italic and bold-italic variants of the fontset as well.
These variant fontsets do not have a short name, only a long one, which
is made by altering fontpattern to indicate the bold or italic
status.
The specification string also says which fonts to use in the fontset. See below for the details.
The construct `charset:font' specifies which font to use (in this fontset) for one particular character set. Here, charset is the name of a character set, and font is the font to use for that character set. You can use this construct any number of times in the specification string.
For the remaining character sets, those that you don't specify explicitly, Emacs chooses a font based on fontpattern: it replaces `fontset-alias' with a value that names one character set. For the ASCII character set, `fontset-alias' is replaced with `ISO8859-1'.
In addition, when several consecutive fields are wildcards, Emacs collapses them into a single wildcard. This is to prevent use of auto-scaled fonts. Fonts made by scaling larger fonts are not usable for editing, and scaling a smaller font is not useful because it is better to use the smaller font in its own size, which Emacs does.
Thus if fontpattern is this,
-*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24
the font specification for ASCII characters would be this:
-*-fixed-medium-r-normal-*-24-*-ISO8859-1
and the font specification for Chinese GB2312 characters would be this:
-*-fixed-medium-r-normal-*-24-*-gb2312*-*
You may not have any Chinese font matching the above font specification. Most X distributions include only Chinese fonts that have `song ti' or `fangsong ti' in the family field. In such a case, `Fontset-n' can be specified as below:
Emacs.Fontset-0: -*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24,\
chinese-gb2312:-*-*-medium-r-normal-*-24-*-gb2312*-*
Then, the font specifications for all but Chinese GB2312 characters have `fixed' in the family field, and the font specification for Chinese GB2312 characters has a wild card `*' in the family field.
t if so; otherwise, nil. The argument frame says
which frame's display to ask about; if frame is omitted or
nil, the selected frame is used.
Note that this does not tell you whether the display you are using really supports that color. You can ask for any defined color on any kind of display, and you will get some result--that is how the X server works. Here's an approximate way to test whether your display supports the color color:
(defun x-color-supported-p (color &optional frame)
(and (x-color-defined-p color frame)
(or (x-display-color-p frame)
(member color '("black" "white"))
(and (> (x-display-planes frame) 1)
(equal color "gray")))))
nil.
(x-color-values "black")
=> (0 0 0)
(x-color-values "white")
=> (65280 65280 65280)
(x-color-values "red")
=> (65280 0 0)
(x-color-values "pink")
=> (65280 49152 51968)
(x-color-values "hungry")
=> nil
The color values are returned for frame's display. If frame
is omitted or nil, the information is returned for the selected
frame's display.
x-get-resource retrieves a resource value from the X
Windows defaults database.
Resources are indexed by a combination of a key and a class. This function searches using a key of the form `instance.attribute' (where instance is the name under which Emacs was invoked), and using `Emacs.class' as the class.
The optional arguments component and subclass add to the key and the class, respectively. You must specify both of them or neither. If you specify them, the key is `instance.component.attribute', and the class is `Emacs.class.subclass'.
x-get-resource
should look up. The default value is "Emacs". You can examine X
resources for application names other than "Emacs" by binding this
variable to some other string, around a call to x-get-resource.
See section `X Resources' in The GNU Emacs Manual.
This section describes functions you can use to get information about
the capabilities and origin of an X display that Emacs is using. Each
of these functions lets you specify the display you are interested in:
the display argument can be either a display name, or a frame
(meaning use the display that frame is on). If you omit the
display argument, or specify nil, that means to use the
selected frame's display.
always, when-mapped, or
not-useful.
nil if the display supports the
SaveUnder feature.
static-gray, gray-scale,
static-color, pseudo-color, true-color, and
direct-color.
t if the screen can display shades of gray.
t if the screen is a color screen.
A position is the index of a character in the text of a buffer. More precisely, a position identifies the place between two characters (or before the first character, or after the last character), so we can speak of the character before or after a given position. However, we often speak of the character "at" a position, meaning the character after that position.
Positions are usually represented as integers starting from 1, but can also be represented as markers---special objects that relocate automatically when text is inserted or deleted so they stay with the surrounding characters. See section Markers.
Point is a special buffer position used by many editing commands, including the self-inserting typed characters and text insertion functions. Other commands move point through the text to allow editing and insertion at different places.
Like other positions, point designates a place between two characters (or before the first character, or after the last character), rather than a particular character. Usually terminals display the cursor over the character that immediately follows point; point is actually before the character on which the cursor sits.
The value of point is a number between 1 and the buffer size plus 1. If narrowing is in effect (see section Narrowing), then point is constrained to fall within the accessible portion of the buffer (possibly at one end of it).
Each buffer has its own value of point, which is independent of the value of point in other buffers. Each window also has a value of point, which is independent of the value of point in other windows on the same buffer. This is why point can have different values in various windows that display the same buffer. When a buffer appears in only one window, the buffer's point and the window's point normally have the same value, so the distinction is rarely important. See section Windows and Point, for more details.
(point)
=> 175
(1+ (buffer-size)), unless narrowing is
in effect, in which case it is the position of the end of the region
that you narrowed to. (See section Narrowing).
(point-min) if flag is less than 1,
(point-max) otherwise. The argument flag must be a number.
point-max returns a value one larger than this.
(buffer-size)
=> 35
(point-max)
=> 36
Motion functions change the value of point, either relative to the current value of point, relative to the beginning or end of the buffer, or relative to the edges of the selected window. See section Point.
These functions move point based on a count of characters.
goto-char is the fundamental primitive; the other functions use
that.
If narrowing is in effect, position still counts from the
beginning of the buffer, but point cannot go outside the accessible
portion. If position is out of range, goto-char moves
point to the beginning or the end of the accessible portion.
When this function is called interactively, position is the numeric prefix argument, if provided; otherwise it is read from the minibuffer.
goto-char returns position.
beginning-of-buffer or end-of-buffer.
In an interactive call, count is the numeric prefix argument.
beginning-of-buffer or end-of-buffer.
In an interactive call, count is the numeric prefix argument.
These functions for parsing words use the syntax table to decide whether a given character is part of a word. See section Syntax Tables.
If it is possible to move count words, without being stopped by
the buffer boundary (except perhaps after the last word), the value is
t. Otherwise, the return value is nil and point stops
at the buffer boundary.
In an interactive call, count is set to the numeric prefix argument.
forward-word, except that it moves
backward until encountering the front of a word, rather than forward.
In an interactive call, count is set to the numeric prefix argument.
This function is rarely used in programs, as it is more efficient to
call forward-word with a negative argument.
forward-word and everything
that uses it. If it is non-nil, then characters in the
"escape" and "character quote" syntax classes count as part of
words. Otherwise, they do not.
To move point to the beginning of the buffer, write:
(goto-char (point-min))
Likewise, to move to the end of the buffer, use:
(goto-char (point-max))
Here are two commands that users use to do these things. They are documented here to warn you not to use them in Lisp programs, because they set the mark and display messages in the echo area.
nil, then it
puts point n tenths of the way from the beginning of the buffer.
In an interactive call, n is the numeric prefix argument,
if provided; otherwise n defaults to nil.
Warning: Don't use this function in Lisp programs!
nil, then it puts
point n tenths of the way from the end of the buffer.
In an interactive call, n is the numeric prefix argument,
if provided; otherwise n defaults to nil.
Warning: Don't use this function in Lisp programs!
Text lines are portions of the buffer delimited by newline characters, which are regarded as part of the previous line. The first text line begins at the beginning of the buffer, and the last text line ends at the end of the buffer whether or not the last character is a newline. The division of the buffer into text lines is not affected by the width of the window, by line continuation in display, or by how tabs and control characters are displayed.
goto-line does not
necessarily move to the beginning of a line.
If narrowing is in effect, then line still counts from the
beginning of the buffer, but point cannot go outside the accessible
portion. So goto-line moves point to the beginning or end of the
accessible portion, if the line number specifies an inaccessible
position.
The return value of goto-line is the difference between
line and the line number of the line to which point actually was
able to move (in the full buffer, before taking account of narrowing).
Thus, the value is positive if the scan encounters the real end of the
buffer before finding the specified line. The value is zero if scan
encounters the end of the accessible portion but not the real end of the
buffer.
In an interactive call, line is the numeric prefix argument if one has been provided. Otherwise line is read in the minibuffer.
nil or 1, it moves forward
count-1 lines and then to the beginning of the line.
If this function reaches the end of the buffer (or of the accessible portion, if narrowing is in effect), it positions point there. No error is signaled.
nil or 1, it moves forward
count-1 lines and then to the end of the line.
If this function reaches the end of the buffer (or of the accessible portion, if narrowing is in effect), it positions point there. No error is signaled.
If forward-line encounters the beginning or end of the buffer (or
of the accessible portion) before finding that many lines, it sets point
there. No error is signaled.
forward-line returns the difference between count and the
number of lines actually moved. If you attempt to move down five lines
from the beginning of a buffer that has only three lines, point stops at
the end of the last line, and the value will be 2.
In an interactive call, count is the numeric prefix argument.
Here is an example of using count-lines:
(defun current-line ()
"Return the vertical position of point..."
(+ (count-lines (window-start) (point))
(if (= (current-column) 0) 1 0)
-1))
Also see the functions bolp and eolp in section Examining Text Near Point.
These functions do not move point, but test whether it is already at the
beginning or end of a line.
The line functions in the previous section count text lines, delimited only by newline characters. By contrast, these functions count screen lines, which are defined by the way the text appears on the screen. A text line is a single screen line if it is short enough to fit the width of the selected window, but otherwise it may occupy several screen lines.
In some cases, text lines are truncated on the screen rather than
continued onto additional screen lines. In these cases,
vertical-motion moves point much like forward-line.
See section Truncation.
Because the width of a given string depends on the flags that control
the appearance of certain characters, vertical-motion behaves
differently, for a given piece of text, depending on the buffer it is
in, and even on the selected window (because the width, the truncation
flag, and display table may vary between windows). See section Usual Display Conventions.
These functions scan text to determine where screen lines break, and thus take time proportional to the distance scanned. If you intend to use them heavily, Emacs provides caches which may improve the performance of your code. See section Truncation.
vertical-motion returns the number of screen lines over which it
moved point. The value may be less in absolute value than count
if the beginning or end of the buffer was reached.
The window window is used for obtaining parameters such as the
width, the horizontal scrolling, and the display table. But
vertical-motion always operates on the current buffer, even if
window currently displays some other buffer.
If count is nil, then point moves to the beginning of the
line in the middle of the window. If the absolute value of count
is greater than the size of the window, then point moves to the place
that would appear on that screen line if the window were tall enough.
This will probably cause the next redisplay to scroll to bring that
location onto the screen.
In an interactive call, count is the numeric prefix argument.
The value returned is the window line number point has moved to, with the top line in the window numbered 0.
The coordinate arguments frompos and topos are cons cells of
the form (hpos . vpos).
The argument width is the number of columns available to display
text; this affects handling of continuation lines. Use the value
returned by window-width for the window of your choice;
normally, use (window-width window).
The argument offsets is either nil or a cons cell of the
form (hscroll . tab-offset). Here hscroll is
the number of columns not being displayed at the left margin; most
callers get this by calling window-hscroll. Meanwhile,
tab-offset is the offset between column numbers on the screen and
column numbers in the buffer. This can be nonzero in a continuation
line, when the previous screen lines' widths do not add up to a multiple
of tab-width. It is always zero in a non-continuation line.
The window window serves only to specify which display table to
use. compute-motion always operates on the current buffer,
regardless of what buffer is displayed in window.
The return value is a list of five elements:
(pos vpos hpos prevhpos contin)
Here pos is the buffer position where the scan stopped, vpos is the vertical screen position, and hpos is the horizontal screen position.
The result prevhpos is the horizontal position one character back
from pos. The result contin is t if the last line
was continued after (or within) the previous character.
For example, to find the buffer position of column col of screen line
line of a certain window, pass the window's display start location
as from and the window's upper-left coordinates as frompos.
Pass the buffer's (point-max) as to, to limit the scan to
the end of the accessible portion of the buffer, and pass line and
col as topos. Here's a function that does this:
(defun coordinates-of-position (col line)
(car (compute-motion (window-start)
'(0 . 0)
(point-max)
(cons col line)
(window-width)
(cons (window-hscroll) 0)
(selected-window))))
When you use compute-motion for the minibuffer, you need to use
minibuffer-prompt-width to get the horizontal position of the
beginning of the first screen line. See section Minibuffer Miscellany.
Here are several functions concerned with balanced-parenthesis expressions (also called sexps in connection with moving across them in Emacs). The syntax table controls how these functions interpret various characters; see section Syntax Tables. See section Parsing Balanced Expressions, for lower-level primitives for scanning sexps or parts of sexps. For user-level commands, see section `Lists Commands' in GNU Emacs Manual.
---------- Buffer: foo ----------
(concat-!- "foo " (car x) y z)
---------- Buffer: foo ----------
(forward-sexp 3)
=> nil
---------- Buffer: foo ----------
(concat "foo " (car x) y-!- z)
---------- Buffer: foo ----------
nil, this variable holds a regular expression that
specifies what text can appear before the open-parenthesis that starts a
defun. That is to say, a defun begins on a line that starts with a
match for this regular expression, followed by a character with
open-parenthesis syntax.
The following two functions move point over a specified set of characters. For example, they are often used to skip whitespace. For related functions, see section Motion and Syntax.
The argument character-set is like the inside of a
`[...]' in a regular expression except that `]' is never
special and `\' quotes `^', `-' or `\'. Thus,
"a-zA-Z" skips over all letters, stopping before the first
nonletter, and "^a-zA-Z" skips nonletters stopping before the
first letter. See section Regular Expressions.
If limit is supplied (it must be a number or a marker), it specifies the maximum position in the buffer that point can be skipped to. Point will stop at or before limit.
In the following example, point is initially located directly before the `T'. After the form is evaluated, point is located at the end of that line (between the `t' of `hat' and the newline). The function skips all letters and spaces, but not newlines.
---------- Buffer: foo ----------
I read "-!-The cat in the hat
comes back" twice.
---------- Buffer: foo ----------
(skip-chars-forward "a-zA-Z ")
=> nil
---------- Buffer: foo ----------
I read "The cat in the hat-!-
comes back" twice.
---------- Buffer: foo ----------
skip-chars-forward except for the direction of motion.
The return value indicates the distance traveled. It is an integer that is zero or less.
It is often useful to move point "temporarily" within a localized
portion of the program, or to switch buffers temporarily. This is
called an excursion, and it is done with the save-excursion
special form. This construct saves the current buffer and its values of
point and the mark so they can be restored after the completion of the
excursion.
The forms for saving and restoring the configuration of windows are described elsewhere (see section Window Configurations, and see section Frame Configurations).
save-excursion special form saves the identity of the current
buffer and the values of point and the mark in it, evaluates
forms, and finally restores the buffer and its saved values of
point and the mark. All three saved values are restored even in case of
an abnormal exit via throw or error (see section Nonlocal Exits).
The save-excursion special form is the standard way to switch
buffers or move point within one part of a program and avoid affecting
the rest of the program. It is used more than 4000 times in the Lisp
sources of Emacs.
save-excursion does not save the values of point and the mark for
other buffers, so changes in other buffers remain in effect after
save-excursion exits.
Likewise, save-excursion does not restore window-buffer
correspondences altered by functions such as switch-to-buffer.
One way to restore these correspondences, and the selected window, is to
use save-window-excursion inside save-excursion
(see section Window Configurations).
The value returned by save-excursion is the result of the last of
forms, or nil if no forms are given.
(save-excursion forms)
==
(let ((old-buf (current-buffer))
(old-pnt (point-marker))
(old-mark (copy-marker (mark-marker))))
(unwind-protect
(progn forms)
(set-buffer old-buf)
(goto-char old-pnt)
(set-marker (mark-marker) old-mark)))
Warning: Ordinary insertion of text adjacent to the saved point value relocates the saved value, just as it relocates all markers. Therefore, when the saved point value is restored, it normally comes before the inserted text.
Although save-excursion saves the location of the mark, it does
not prevent functions which modify the buffer from setting
deactivate-mark, and thus causing the deactivation of the mark
after the command finishes. See section The Mark.
Narrowing means limiting the text addressable by Emacs editing commands to a limited range of characters in a buffer. The text that remains addressable is called the accessible portion of the buffer.
Narrowing is specified with two buffer positions which become the beginning and end of the accessible portion. For most editing commands and most Emacs primitives, these positions replace the values of the beginning and end of the buffer. While narrowing is in effect, no text outside the accessible portion is displayed, and point cannot move outside the accessible portion.
Values such as positions or line numbers, which usually count from the beginning of the buffer, do so despite narrowing, but the functions which use them refuse to operate on text that is inaccessible.
The commands for saving buffers are unaffected by narrowing; they save the entire buffer regardless of any narrowing.
In an interactive call, start and end are set to the bounds of the current region (point and the mark, with the smallest first).
nil means to move forward or backward by
move-count pages and then narrow to one page. The variable
page-delimiter specifies where pages start and end
(see section Standard Regular Expressions Used in Editing).
In an interactive call, move-count is set to the numeric prefix argument.
(narrow-to-region 1 (1+ (buffer-size)))
throw or error (see section Nonlocal Exits).
Therefore, this construct is a clean way to narrow a buffer temporarily.
The value returned by save-restriction is that returned by the
last form in body, or nil if no body forms were given.
Caution: it is easy to make a mistake when using the
save-restriction construct. Read the entire description here
before you try it.
If body changes the current buffer, save-restriction still
restores the restrictions on the original buffer (the buffer whose
restrictions it saved from), but it does not restore the identity of the
current buffer.
save-restriction does not restore point and the mark; use
save-excursion for that. If you use both save-restriction
and save-excursion together, save-excursion should come
first (on the outside). Otherwise, the old point value would be
restored with temporary narrowing still in effect. If the old point
value were outside the limits of the temporary narrowing, this would
fail to restore it accurately.
The save-restriction special form records the values of the
beginning and end of the accessible portion as distances from the
beginning and end of the buffer. In other words, it records the amount
of inaccessible text before and after the accessible portion.
This method yields correct results if body does further narrowing.
However, save-restriction can become confused if the body widens
and then makes changes outside the range of the saved narrowing. When
this is what you want to do, save-restriction is not the right
tool for the job. Here is what you must use instead:
(let ((beg (point-min-marker))
(end (point-max-marker)))
(unwind-protect
(progn body)
(save-excursion
(set-buffer (marker-buffer beg))
(narrow-to-region beg end))))
Here is a simple example of correct use of save-restriction:
---------- Buffer: foo ----------
This is the contents of foo
This is the contents of foo
This is the contents of foo-!-
---------- Buffer: foo ----------
(save-excursion
(save-restriction
(goto-char 1)
(forward-line 2)
(narrow-to-region 1 (point))
(goto-char (point-min))
(replace-string "foo" "bar")))
---------- Buffer: foo ----------
This is the contents of bar
This is the contents of bar
This is the contents of foo-!-
---------- Buffer: foo ----------
A marker is a Lisp object used to specify a position in a buffer relative to the surrounding text. A marker changes its offset from the beginning of the buffer automatically whenever text is inserted or deleted, so that it stays with the two characters on either side of it.
A marker specifies a buffer and a position in that buffer. The marker can be used to represent a position in the functions that require one, just as an integer could be used. See section Positions, for a complete description of positions.
A marker has two attributes: the marker position, and the marker buffer. The marker position is an integer that is equivalent (at a given time) to the marker as a position in that buffer. But the marker's position value can change often during the life of the marker. Insertion and deletion of text in the buffer relocate the marker. The idea is that a marker positioned between two characters remains between those two characters despite insertion and deletion elsewhere in the buffer. Relocation changes the integer equivalent of the marker.
Deleting text around a marker's position leaves the marker between the
characters immediately before and after the deleted text. Inserting
text at the position of a marker normally leaves the marker either in
front of or after the new text, depending on the marker's insertion
type (see section Marker Insertion Types)---unless the insertion is done
with insert-before-markers (see section Inserting Text).
Insertion and deletion in a buffer must check all the markers and relocate them if necessary. This slows processing in a buffer with a large number of markers. For this reason, it is a good idea to make a marker point nowhere if you are sure you don't need it any more. Unreferenced markers are garbage collected eventually, but until then will continue to use time if they do point somewhere.
Because it is common to perform arithmetic operations on a marker
position, most of the arithmetic operations (including + and
-) accept markers as arguments. In such cases, the marker
stands for its current position.
Here are examples of creating markers, setting markers, and moving point to markers:
;; Make a new marker that initially does not point anywhere:
(setq m1 (make-marker))
=> #<marker in no buffer>
;; Set m1 to point between the 99th and 100th characters
;; in the current buffer:
(set-marker m1 100)
=> #<marker at 100 in markers.texi>
;; Now insert one character at the beginning of the buffer:
(goto-char (point-min))
=> 1
(insert "Q")
=> nil
;; m1 is updated appropriately.
m1
=> #<marker at 101 in markers.texi>
;; Two markers that point to the same position
;; are not eq, but they are equal.
(setq m2 (copy-marker m1))
=> #<marker at 101 in markers.texi>
(eq m1 m2)
=> nil
(equal m1 m2)
=> t
;; When you are finished using a marker, make it point nowhere.
(set-marker m1 nil)
=> #<marker in no buffer>
You can test an object to see whether it is a marker, or whether it is either an integer or a marker. The latter test is useful in connection with the arithmetic functions that work with both markers and integers.
t if object is a marker, nil
otherwise. Note that integers are not markers, even though many
functions will accept either a marker or an integer.
t if object is an integer or a marker,
nil otherwise.
t if object is a number (either
integer or floating point) or a marker, nil otherwise.
When you create a new marker, you can make it point nowhere, or point to the present position of point, or to the beginning or end of the accessible portion of the buffer, or to the same place as another given marker.
(make-marker)
=> #<marker in no buffer>
copy-marker, below.
Here are examples of this function and point-min-marker, shown in
a buffer containing a version of the source file for the text of this
chapter.
(point-min-marker)
=> #<marker at 1 in markers.texi>
(point-max-marker)
=> #<marker at 15573 in markers.texi>
(narrow-to-region 100 200)
=> nil
(point-min-marker)
=> #<marker at 100 in markers.texi>
(point-max-marker)
=> #<marker at 200 in markers.texi>
copy-marker returns a
new marker that points to the same place and the same buffer as does
marker-or-integer. If passed an integer as its argument,
copy-marker returns a new marker that points to position
marker-or-integer in the current buffer.
The new marker's insertion type is specified by the argument insertion-type. See section Marker Insertion Types.
If passed an integer argument less than 1, copy-marker returns a
new marker that points to the beginning of the current buffer. If
passed an integer argument greater than the length of the buffer,
copy-marker returns a new marker that points to the end of the
buffer.
(copy-marker 0)
=> #<marker at 1 in markers.texi>
(copy-marker 20000)
=> #<marker at 7572 in markers.texi>
An error is signaled if marker is neither a marker nor an integer.
Two distinct markers are considered equal (even though not
eq) to each other if they have the same position and buffer, or
if they both point nowhere.
(setq p (point-marker))
=> #<marker at 2139 in markers.texi>
(setq q (copy-marker p))
=> #<marker at 2139 in markers.texi>
(eq p q)
=> nil
(equal p q)
=> t
This section describes the functions for accessing the components of a marker object.
nil if it points nowhere.
nil if it points nowhere.
(setq m (make-marker))
=> #<marker in no buffer>
(marker-position m)
=> nil
(marker-buffer m)
=> nil
(set-marker m 3770 (current-buffer))
=> #<marker at 3770 in markers.texi>
(marker-buffer m)
=> #<buffer markers.texi>
(marker-position m)
=> 3770
When you insert text directly at the place where a marker points,
there are two possible ways to relocate that marker: it can point before
the inserted text, or point after it. You can specify which one a given
marker should do by setting its insertion type. Note that use of
insert-before-markers ignores markers' insertion types, always
relocating a marker to point after the inserted text.
t, marker will advance when
text is inserted at its position. If type is nil,
marker does not advance when text is inserted there.
This section describes how to change the position of an existing marker. When you do this, be sure you know whether the marker is used outside of your program, and, if so, what effects will result from moving it--otherwise, confusing things may happen in other parts of Emacs.
If position is less than 1, set-marker moves marker
to the beginning of the buffer. If position is greater than the
size of the buffer, set-marker moves marker to the end of the
buffer. If position is nil or a marker that points
nowhere, then marker is set to point nowhere.
The value returned is marker.
(setq m (point-marker))
=> #<marker at 4714 in markers.texi>
(set-marker m 55)
=> #<marker at 55 in markers.texi>
(setq b (get-buffer "foo"))
=> #<buffer foo>
(set-marker m 0 b)
=> #<marker at 1 in foo>
set-marker.
One special marker in each buffer is designated the mark. It
records a position for the user for the sake of commands such as
kill-region and indent-rigidly. Lisp programs should set
the mark only to values that have a potential use to the user, and never
for their own internal purposes. For example, the replace-regexp
command sets the mark to the value of point before doing any
replacements, because this enables the user to move back there
conveniently after the replace is finished.
Many commands are designed so that when called interactively they
operate on the text between point and the mark. If you are writing such
a command, don't examine the mark directly; instead, use
interactive with the `r' specification. This provides the
values of point and the mark as arguments to the command in an
interactive call, but permits other Lisp programs to specify arguments
explicitly. See section Code Characters for interactive.
Each buffer has its own value of the mark that is independent of the value of the mark in other buffers. When a buffer is created, the mark exists but does not point anywhere. We consider this state as "the absence of a mark in that buffer."
Once the mark "exists" in a buffer, it normally never ceases to
exist. However, it may become inactive, if Transient Mark mode is
enabled. The variable mark-active, which is always buffer-local
in all buffers, indicates whether the mark is active: non-nil
means yes. A command can request deactivation of the mark upon return
to the editor command loop by setting deactivate-mark to a
non-nil value (but this causes deactivation only if Transient
Mark mode is enabled).
The main motivation for using Transient Mark mode is that this mode also enables highlighting of the region when the mark is active. See section Emacs Display.
In addition to the mark, each buffer has a mark ring which is a
list of markers containing previous values of the mark. When editing
commands change the mark, they should normally save the old value of the
mark on the mark ring. The variable mark-ring-max specifies the
maximum number of entries in the mark ring; once the list becomes this
long, adding a new element deletes the last element.
If the mark is inactive, mark normally signals an error.
However, if force is non-nil, then mark returns the
mark position anyway--or nil, if the mark is not yet set for
this buffer.
(setq m (mark-marker))
=> #<marker at 3420 in markers.texi>
(set-marker m 100)
=> #<marker at 100 in markers.texi>
(mark-marker)
=> #<marker at 100 in markers.texi>
Like any marker, this marker can be set to point at any buffer you like. We don't recommend that you make it point at any buffer other than the one of which it is the mark. If you do, it will yield perfectly consistent, but rather odd, results.
Please note: Use this function only if you want the user to
see that the mark has moved, and you want the previous mark position to
be lost. Normally, when a new mark is set, the old one should go on the
mark-ring. For this reason, most applications should use
push-mark and pop-mark, not set-mark.
Novice Emacs Lisp programmers often try to use the mark for the wrong purposes. The mark saves a location for the user's convenience. An editing command should not alter the mark unless altering the mark is part of the user-level functionality of the command. (And, in that case, this effect should be documented.) To remember a location for internal use in the Lisp program, store it in a Lisp variable. For example:
(let ((beg (point))) (forward-line 1) (delete-region beg (point))).
mark-ring. If
position is nil, then the value of point is used.
push-mark returns nil.
The function push-mark normally does not activate the
mark. To do that, specify t for the argument activate.
A `Mark set' message is displayed unless nomsg is
non-nil.
mark-ring and makes
that mark become the buffer's actual mark. This does not move point in
the buffer, and it does nothing if mark-ring is empty. It
deactivates the mark.
The return value is not meaningful.
nil enables Transient Mark mode, in which
every buffer-modifying primitive sets deactivate-mark. The
consequence of this is that commands that modify the buffer normally
make the mark inactive.
nil, Lisp programs and the Emacs user can use the
mark even when it is inactive. This option affects the behavior of
Transient Mark mode. When the option is non-nil, deactivation of
the mark turns off region highlighting, but commands that use the mark
behave as if the mark were still active.
nil, then the editor
command loop deactivates the mark after the command returns (if
Transient Mark mode is enabled). All the primitives that change the
buffer set deactivate-mark, to deactivate the mark when the
command is finished.
nil. This variable
is always buffer-local in each buffer.
activate-mark-hook is
also run at the end of a command if the mark is active and it is
possible that the region may have changed.
mark-ring
=> (#<marker at 11050 in markers.texi>
#<marker at 10832 in markers.texi>
...)
mark-ring. If
more marks than this are pushed onto the mark-ring,
push-mark discards an old mark when it adds a new one.
The text between point and the mark is known as the region. Various functions operate on text delimited by point and the mark, but only those functions specifically related to the region itself are described here.
If the mark does not point anywhere, an error is signaled.
If the mark does not point anywhere, an error is signaled.
Few programs need to use the region-beginning and
region-end functions. A command designed to operate on a region
should normally use interactive with the `r' specification
to find the beginning and end of the region. This lets other Lisp
programs specify the bounds explicitly as arguments. (See section Code Characters for interactive.)
This chapter describes the functions that deal with the text in a buffer. Most examine, insert, or delete text in the current buffer, often in the vicinity of point. Many are interactive. All the functions that change the text provide for undoing the changes (see section Undo).
Many text-related functions operate on a region of text defined by two
buffer positions passed in arguments named start and end.
These arguments should be either markers (see section Markers) or numeric
character positions (see section Positions). The order of these arguments
does not matter; it is all right for start to be the end of the
region and end the beginning. For example, (delete-region 1
10) and (delete-region 10 1) are equivalent. An
args-out-of-range error is signaled if either start or
end is outside the accessible portion of the buffer. In an
interactive call, point and the mark are used for these arguments.
Throughout this chapter, "text" refers to the characters in the buffer, together with their properties (when relevant).
Many functions are provided to look at the characters around point.
Several simple functions are described here. See also looking-at
in section Regular Expression Searching.
nil. The default for
position is point.
In the following example, assume that the first character in the buffer is `@':
(char-to-string (char-after 1))
=> "@"
nil. The default for
position is point.
(char-after (point)). However, if
point is at the end of the buffer, then following-char returns 0.
Remember that point is always between characters, and the terminal
cursor normally appears over the character following point. Therefore,
the character returned by following-char is the character the
cursor is over.
In this example, point is between the `a' and the `c'.
---------- Buffer: foo ----------
Gentlemen may cry ``Pea-!-ce! Peace!,''
but there is no peace.
---------- Buffer: foo ----------
(char-to-string (preceding-char))
=> "a"
(char-to-string (following-char))
=> "c"
following-char, for an example. If
point is at the beginning of the buffer, preceding-char returns
0.
t if point is at the beginning of the
buffer. If narrowing is in effect, this means the beginning of the
accessible portion of the text. See also point-min in
section Point.
t if point is at the end of the buffer.
If narrowing is in effect, this means the end of accessible portion of
the text. See also point-max in See section Point.
t if point is at the beginning of a line.
See section Motion by Text Lines. The beginning of the buffer (or of its accessible
portion) always counts as the beginning of a line.
t if point is at the end of a line. The
end of the buffer (or of its accessible portion) is always considered
the end of a line.
This section describes two functions that allow a Lisp program to convert any portion of the text in the buffer into a string.
buffer-substring signals an args-out-of-range
error.
It is not necessary for start to be less than end; the arguments can be given in either order. But most often the smaller argument is written first.
If the text being copied has any text properties, these are copied into the string along with the characters they belong to. See section Text Properties. However, overlays (see section Overlays) in the buffer and their properties are ignored, not copied.
---------- Buffer: foo ---------- This is the contents of buffer foo ---------- Buffer: foo ---------- (buffer-substring 1 10) => "This is t" (buffer-substring (point-max) 10) => "he contents of buffer foo "
buffer-substring, except that it does not copy text
properties, just the characters themselves. See section Text Properties.
(buffer-substring (point-min) (point-max))
---------- Buffer: foo ----------
This is the contents of buffer foo
---------- Buffer: foo ----------
(buffer-string)
=> "This is the contents of buffer foo
"
The argument thing is a symbol which specifies a kind of syntactic
entity. Possibilities include symbol, list, sexp,
defun, filename, url, word, sentence,
whitespace, line, page, and others.
---------- Buffer: foo ----------
Gentlemen may cry ``Pea-!-ce! Peace!,''
but there is no peace.
---------- Buffer: foo ----------
(thing-at-point 'word)
=> "Peace"
(thing-at-point 'line)
=> "Gentlemen may cry ``Peace! Peace!,''\n"
(thing-at-point 'whitespace)
=> nil
This function lets you compare portions of the text in a buffer, without copying them into strings first.
nil for buffer1, buffer2, or both to stand for the
current buffer.
The value is negative if the first substring is less, positive if the first is greater, and zero if they are equal. The absolute value of the result is one plus the index of the first differing characters within the substrings.
This function ignores case when comparing characters
if case-fold-search is non-nil. It always ignores
text properties.
Suppose the current buffer contains the text `foobarbar haha!rara!'; then in this example the two substrings are `rbar ' and `rara!'. The value is 2 because the first substring is greater at the second character.
(compare-buffer-substring nil 6 11 nil 16 21)
=> 2
Insertion means adding new text to a buffer. The inserted text goes at point--between the character before point and the character after point. Some insertion functions leave point before the inserted text, while other functions leave it after. We call the former insertion after point and the latter insertion before point.
Insertion relocates markers that point at positions after the
insertion point, so that they stay with the surrounding text
(see section Markers). When a marker points at the place of insertion,
insertion may or may not relocate the marker, depending on the marker's
insertion type (see section Marker Insertion Types). Certain special
functions such as insert-before-markers relocate all such markers
to point after the inserted text, regardless of the markers' insertion
type.
Insertion functions signal an error if the current buffer is read-only.
These functions copy text characters from strings and buffers along with their properties. The inserted characters have exactly the same properties as the characters they were copied from. By contrast, characters specified as separate arguments, not part of a string or buffer, inherit their text properties from the neighboring text.
The insertion functions convert text from unibyte to multibyte in order to insert in a multibyte buffer, and vice versa--if the text comes from a string or from a buffer. However, they do not convert unibyte character codes 128 through 255 to multibyte characters, not even if the current buffer is a multibyte buffer. See section Converting Text Representations.
nil.
nil.
This function is unlike the other insertion functions in that it relocates markers initially pointing at the insertion point, to point after the inserted text. If an overlay begins the insertion point, the inserted text falls outside the overlay; if a nonempty overlay ends at the insertion point, the inserted text falls inside that overlay.
nil means 1), and character must be a character.
The value is nil.
This function does not convert unibyte character codes 128 through 255 to multibyte characters, not even if the current buffer is a multibyte buffer. See section Converting Text Representations.
If inherit is non-nil, then the inserted characters inherit
sticky text properties from the two characters before and after the
insertion point. See section Stickiness of Text Properties.
nil.
In this example, the form is executed with buffer `bar' as the current buffer. We assume that buffer `bar' is initially empty.
---------- Buffer: foo ----------
We hold these truths to be self-evident, that all
---------- Buffer: foo ----------
(insert-buffer-substring "foo" 1 20)
=> nil
---------- Buffer: bar ----------
We hold these truth-!-
---------- Buffer: bar ----------
See section Stickiness of Text Properties, for other insertion functions that inherit text properties from the nearby text in addition to inserting it. Whitespace inserted by indentation functions also inherits text properties.
This section describes higher-level commands for inserting text, commands intended primarily for the user but useful also in Lisp programs.
nil.
nil. Most printing characters
are bound to this command. In routine use, self-insert-command
is the most frequently called function in Emacs, but programs rarely use
it except to install it on a keymap.
In an interactive call, count is the numeric prefix argument.
This command calls auto-fill-function whenever that is
non-nil and the character inserted is a space or a newline
(see section Auto Filling).
This command performs abbrev expansion if Abbrev mode is enabled and the inserted character does not have word-constituent syntax. (See section Abbrevs And Abbrev Expansion, and section Table of Syntax Classes.)
This is also responsible for calling blink-paren-function when
the inserted character has close parenthesis syntax (see section Blinking Parentheses).
This function calls auto-fill-function if the current column
number is greater than the value of fill-column and
number-of-newlines is nil. Typically what
auto-fill-function does is insert a newline; thus, the overall
result in this case is to insert two newlines at different places: one
at point, and another earlier in the line. newline does not
auto-fill if number-of-newlines is non-nil.
This command indents to the left margin if that is not zero. See section Margins for Filling.
The value returned is nil. In an interactive call, count
is the numeric prefix argument.
indent-to function.
split-line returns the position of point.
Programs hardly ever use this function.
overwrite-mode-textual, overwrite-mode-binary,
or nil. overwrite-mode-textual specifies textual
overwrite mode (treats newlines and tabs specially), and
overwrite-mode-binary specifies binary overwrite mode (treats
newlines and tabs like any other characters).
Deletion means removing part of the text in a buffer, without saving it in the kill ring (see section The Kill Ring). Deleted text can't be yanked, but can be reinserted using the undo mechanism (see section Undo). Some deletion functions do save text in the kill ring in some special cases.
All of the deletion functions operate on the current buffer, and all
return a value of nil.
buffer-read-only
error. Otherwise, it deletes the text without asking for any
confirmation. It returns nil.
Normally, deleting a large amount of text from a buffer inhibits further
auto-saving of that buffer "because it has shrunk". However,
erase-buffer does not do this, the idea being that the future
text is not really related to the former text, and its size should not
be compared with that of the former text.
nil. If
point was inside the deleted region, its value afterward is start.
Otherwise, point relocates with the surrounding text, as markers do.
nil, then it saves the deleted characters in the kill ring.
In an interactive call, count is the numeric prefix argument, and killp is the unprocessed prefix argument. Therefore, if a prefix argument is supplied, the text is saved in the kill ring. If no prefix argument is supplied, then one character is deleted, but not saved in the kill ring.
The value returned is always nil.
nil, then it saves the deleted characters in the kill ring.
In an interactive call, count is the numeric prefix argument, and killp is the unprocessed prefix argument. Therefore, if a prefix argument is supplied, the text is saved in the kill ring. If no prefix argument is supplied, then one character is deleted, but not saved in the kill ring.
The value returned is always nil.
nil, then the command saves the deleted
characters in the kill ring.
Conversion of tabs to spaces happens only if count is positive. If it is negative, exactly -count characters after point are deleted.
In an interactive call, count is the numeric prefix argument, and killp is the unprocessed prefix argument. Therefore, if a prefix argument is supplied, the text is saved in the kill ring. If no prefix argument is supplied, then one character is deleted, but not saved in the kill ring.
The value returned is always nil.
backward-delete-char-untabify should
deal with whitespace. Possible values include untabify, the
default, meaning convert a tab to many spaces and delete one;
hungry, meaning delete all the whitespace characters before point
with one command, and nil, meaning do nothing special for
whitespace characters.
This section describes higher-level commands for deleting text, commands intended primarily for the user but useful also in Lisp programs.
nil.
In the following examples, we call delete-horizontal-space four
times, once on each line, with point between the second and third
characters on the line each time.
---------- Buffer: foo ----------
I -!-thought
I -!- thought
We-!- thought
Yo-!-u thought
---------- Buffer: foo ----------
(delete-horizontal-space) ; Four times.
=> nil
---------- Buffer: foo ----------
Ithought
Ithought
Wethought
You thought
---------- Buffer: foo ----------
nil,
delete-indentation joins this line to the following line
instead. The function returns nil.
If there is a fill prefix, and the second of the lines being joined
starts with the prefix, then delete-indentation deletes the
fill prefix before joining the lines. See section Margins for Filling.
In the example below, point is located on the line starting `events', and it makes no difference if there are trailing spaces in the preceding line.
---------- Buffer: foo ----------
When in the course of human
-!- events, it becomes necessary
---------- Buffer: foo ----------
(delete-indentation)
=> nil
---------- Buffer: foo ----------
When in the course of human-!- events, it becomes necessary
---------- Buffer: foo ----------
After the lines are joined, the function fixup-whitespace is
responsible for deciding whether to leave a space at the junction.
nil.
At the beginning or end of a line, the appropriate amount of space is none. Before a character with close parenthesis syntax, or after a character with open parenthesis or expression-prefix syntax, no space is also appropriate. Otherwise, one space is appropriate. See section Table of Syntax Classes.
In the example below, fixup-whitespace is called the first time
with point before the word `spaces' in the first line. For the
second invocation, point is directly after the `('.
---------- Buffer: foo ----------
This has too many -!-spaces
This has too many spaces at the start of (-!- this list)
---------- Buffer: foo ----------
(fixup-whitespace)
=> nil
(fixup-whitespace)
=> nil
---------- Buffer: foo ----------
This has too many spaces
This has too many spaces at the start of (this list)
---------- Buffer: foo ----------
nil.
A blank line is defined as a line containing only tabs and spaces.
delete-blank-lines returns nil.
Kill functions delete text like the deletion functions, but save it so that the user can reinsert it by yanking. Most of these functions have `kill-' in their name. By contrast, the functions whose names start with `delete-' normally do not save text for yanking (though they can still be undone); these are "deletion" functions.
Most of the kill commands are primarily for interactive use, and are not described here. What we do describe are the functions provided for use in writing such commands. You can use these functions to write commands for killing text. When you need to delete text for internal purposes within a Lisp function, you should normally use deletion functions, so as not to disturb the kill ring contents. See section Deleting Text.
Killed text is saved for later yanking in the kill ring. This
is a list that holds a number of recent kills, not just the last text
kill. We call this a "ring" because yanking treats it as having
elements in a cyclic order. The list is kept in the variable
kill-ring, and can be operated on with the usual functions for
lists; there are also specialized functions, described in this section,
that treat it as a ring.
Some people think this use of the word "kill" is unfortunate, since it refers to operations that specifically do not destroy the entities "killed". This is in sharp contrast to ordinary life, in which death is permanent and "killed" entities do not come back to life. Therefore, other metaphors have been proposed. For example, the term "cut ring" makes sense to people who, in pre-computer days, used scissors and paste to cut up and rearrange manuscripts. However, it would be difficult to change the terminology now.
The kill ring records killed text as strings in a list, most recent first. A short kill ring, for example, might look like this:
("some text" "a different piece of text" "even older text")
When the list reaches kill-ring-max entries in length, adding a
new entry automatically deletes the last entry.
When kill commands are interwoven with other commands, each kill command makes a new entry in the kill ring. Multiple kill commands in succession build up a single kill-ring entry, which would be yanked as a unit; the second and subsequent consecutive kill commands add text to the entry made by the first one.
For yanking, one entry in the kill ring is designated the "front" of the ring. Some yank commands "rotate" the ring by designating a different element as the "front." But this virtual rotation doesn't change the list itself--the most recent entry always comes first in the list.
kill-region is the usual subroutine for killing text. Any
command that calls this function is a "kill command" (and should
probably have `kill' in its name). kill-region puts the
newly killed text in a new element at the beginning of the kill ring or
adds it to the most recent element. It determines automatically (using
last-command) whether the previous command was a kill command,
and if so appends the killed text to the most recent entry.
nil.
In an interactive call, start and end are point and the mark.
If the buffer is read-only, kill-region modifies the kill ring
just the same, then signals an error without modifying the buffer. This
is convenient because it lets the user use all the kill commands to copy
text into the kill ring from a read-only buffer.
nil, kill-region does not get an
error if the buffer is read-only. Instead, it simply returns, updating
the kill ring but not changing the buffer.
nil. It also indicates the extent
of the text copied by moving the cursor momentarily, or by displaying a
message in the echo area.
The command does not set this-command to kill-region, so a
subsequent kill command does not append to the same kill ring entry.
Don't call copy-region-as-kill in Lisp programs unless you aim to
support Emacs 18. For newer Emacs versions, it is better to use
kill-new or kill-append instead. See section Low-Level Kill Ring.
Yanking means reinserting an entry of previously killed text from the kill ring. The text properties are copied too.
If arg is a list (which occurs interactively when the user
types C-u with no digits), then yank inserts the text as
described above, but puts point before the yanked text and puts the mark
after it.
If arg is a number, then yank inserts the argth most
recently killed text--the argth element of the kill ring list.
yank does not alter the contents of the kill ring or rotate it.
It returns nil.
This is allowed only immediately after a yank or another
yank-pop. At such a time, the region contains text that was just
inserted by yanking. yank-pop deletes that text and inserts in
its place a different piece of killed text. It does not add the deleted
text to the kill ring, since it is already in the kill ring somewhere.
If arg is nil, then the replacement text is the previous
element of the kill ring. If arg is numeric, the replacement is
the argth previous kill. If arg is negative, a more recent
kill is the replacement.
The sequence of kills in the kill ring wraps around, so that after the oldest one comes the newest one, and before the newest one goes the oldest.
The return value is always nil.
These functions and variables provide access to the kill ring at a lower level, but still convenient for use in Lisp programs, because they take care of interaction with window system selections (see section Window System Selections).
current-kill rotates the yanking pointer, which
designates the "front" of the kill ring, by n places (from newer
kills to older ones), and returns the text at that place in the ring.
If the optional second argument do-not-move is non-nil,
then current-kill doesn't alter the yanking pointer; it just
returns the nth kill, counting from the current yanking pointer.
If n is zero, indicating a request for the latest kill,
current-kill calls the value of
interprogram-paste-function (documented below) before consulting
the kill ring.
interprogram-cut-function (see below).
nil, it goes at the beginning. This
function also invokes the value of interprogram-cut-function (see
below).
nil or a function of no arguments.
If the value is a function, current-kill calls it to get the
"most recent kill". If the function returns a non-nil value,
then that value is used as the "most recent kill". If it returns
nil, then the first element of kill-ring is used.
The normal use of this hook is to get the window system's primary selection as the most recent kill, even if the selection belongs to another application. See section Window System Selections.
nil or a function of one argument.
If the value is a function, kill-new and kill-append call
it with the new first element of the kill ring as an argument.
The normal use of this hook is to set the window system's primary selection from the newly killed text. See section Window System Selections.
The variable kill-ring holds the kill ring contents, in the
form of a list of strings. The most recent kill is always at the front
of the list.
The kill-ring-yank-pointer variable points to a link in the
kill ring list, whose CAR is the text to yank next. We say it
identifies the "front" of the ring. Moving
kill-ring-yank-pointer to a different link is called
rotating the kill ring. We call the kill ring a "ring" because
the functions that move the yank pointer wrap around from the end of the
list to the beginning, or vice-versa. Rotation of the kill ring is
virtual; it does not change the value of kill-ring.
Both kill-ring and kill-ring-yank-pointer are Lisp
variables whose values are normally lists. The word "pointer" in the
name of the kill-ring-yank-pointer indicates that the variable's
purpose is to identify one element of the list for use by the next yank
command.
The value of kill-ring-yank-pointer is always eq to one
of the links in the kill ring list. The element it identifies is the
CAR of that link. Kill commands, which change the kill ring, also
set this variable to the value of kill-ring. The effect is to
rotate the ring so that the newly killed text is at the front.
Here is a diagram that shows the variable kill-ring-yank-pointer
pointing to the second entry in the kill ring ("some text" "a
different piece of text" "yet older text").
kill-ring ---- kill-ring-yank-pointer
| |
| v
| --- --- --- --- --- ---
--> | | |------> | | |--> | | |--> nil
--- --- --- --- --- ---
| | |
| | |
| | -->"yet older text"
| |
| --> "a different piece of text"
|
--> "some text"
This state of affairs might occur after C-y (yank)
immediately followed by M-y (yank-pop).
kill-ring, and its CAR is the kill string
that C-y should yank.
kill-ring-max is 30.
Most buffers have an undo list, which records all changes made
to the buffer's text so that they can be undone. (The buffers that
don't have one are usually special-purpose buffers for which Emacs
assumes that undoing is not useful.) All the primitives that modify the
text in the buffer automatically add elements to the front of the undo
list, which is in the variable buffer-undo-list.
t disables the recording of undo information.
Here are the kinds of elements an undo list can have:
position
(beg . end)
(text . position)
(abs position).
(t high . low)
primitive-undo uses those
values to determine whether to mark the buffer as unmodified once again;
it does so only if the file's modification time matches those numbers.
(nil property value beg . end)
(put-text-property beg end property value)
(marker . adjustment)
nil
nil.
The editor command loop automatically creates an undo boundary before each key sequence is executed. Thus, each undo normally undoes the effects of one command. Self-inserting input characters are an exception. The command loop makes a boundary for the first such character; the next 19 consecutive self-inserting input characters do not make boundaries, and then the 20th does, and so on as long as self-inserting characters continue.
All buffer modifications add a boundary whenever the previous undoable change was made in some other buffer. This is to ensure that each command makes a boundary in each buffer where it makes changes.
Calling this function explicitly is useful for splitting the effects of
a command into more than one unit. For example, query-replace
calls undo-boundary after each replacement, so that the user can
undo individual replacements one by one.
primitive-undo adds elements to the buffer's undo list when it
changes the buffer. Undo commands avoid confusion by saving the undo
list value at the beginning of a sequence of undo operations. Then the
undo operations use and update the saved value. The new elements added
by undoing are not part of this saved value, so they don't interfere with
continuing to undo.
This section describes how to enable and disable undo information for a given buffer. It also explains how the undo list is truncated automatically so it doesn't get too big.
Recording of undo information in a newly created buffer is normally
enabled to start with; but if the buffer name starts with a space, the
undo recording is initially disabled. You can explicitly enable or
disable undo recording with the following two functions, or by setting
buffer-undo-list yourself.
nil.
In an interactive call, buffer-or-name is the current buffer. You cannot specify any other buffer.
This function returns nil.
The name buffer-flush-undo is not considered obsolete, but the
preferred name is buffer-disable-undo.
As editing continues, undo lists get longer and longer. To prevent
them from using up all available memory space, garbage collection trims
them back to size limits you can set. (For this purpose, the "size"
of an undo list measures the cons cells that make up the list, plus the
strings of deleted text.) Two variables control the range of acceptable
sizes: undo-limit and undo-strong-limit.
Filling means adjusting the lengths of lines (by moving the line
breaks) so that they are nearly (but no greater than) a specified
maximum width. Additionally, lines can be justified, which means
inserting spaces to make the left and/or right margins line up
precisely. The width is controlled by the variable fill-column.
For ease of reading, lines should be no longer than 70 or so columns.
You can use Auto Fill mode (see section Auto Filling) to fill text automatically as you insert it, but changes to existing text may leave it improperly filled. Then you must fill the text explicitly.
Most of the commands in this section return values that are not
meaningful. All the functions that do filling take note of the current
left margin, current right margin, and current justification style
(see section Margins for Filling). If the current justification style is
none, the filling functions don't actually do anything.
Several of the filling functions have an argument justify.
If it is non-nil, that requests some kind of justification. It
can be left, right, full, or center, to
request a specific style of justification. If it is t, that
means to use the current justification style for this part of the text
(see current-justification, below). Any other value is treated
as full.
When you call the filling functions interactively, using a prefix
argument implies the value full for justify.
nil, each line is justified as well.
It uses the ordinary paragraph motion commands to find paragraph
boundaries. See section `Paragraphs' in The Emacs Manual.
nil.
If nosqueeze is non-nil, that means to leave whitespace
other than line breaks untouched. If to-eop is non-nil,
that means to keep filling to the end of the paragraph--or the next hard
newline, if use-hard-newlines is enabled (see below).
The variable paragraph-separate controls how to distinguish
paragraphs. See section Standard Regular Expressions Used in Editing.
The first two arguments, start and end, are the beginning
and end of the region to be filled. The third and fourth arguments,
justify and mail-flag, are optional. If
justify is non-nil, the paragraphs are justified as
well as filled. If mail-flag is non-nil, it means the
function is operating on a mail message and therefore should not fill
the header lines.
Ordinarily, fill-individual-paragraphs regards each change in
indentation as starting a new paragraph. If
fill-individual-varying-indent is non-nil, then only
separator lines separate paragraphs. That mode can handle indented
paragraphs with additional indentation on the first line.
fill-individual-paragraphs as
described above.
nil.
In an interactive call, any prefix argument requests justification.
If nosqueeze is non-nil, that means to leave whitespace
other than line breaks untouched. If squeeze-after is
non-nil, it specifies a position in the region, and means don't
canonicalize spaces before that position.
In Adaptive Fill mode, this command calls fill-context-prefix to
choose a fill prefix by default. See section Adaptive Fill Mode.
fill-column. It returns
nil.
The argument how, if non-nil specifies explicitly the style
of justification. It can be left, right, full,
center, or none. If it is t, that means to do
follow specified justification style (see current-justification,
below). nil means to do full justification.
If eop is non-nil, that means do left-justification if
current-justification specifies full justification. This is used
for the last line of a paragraph; even if the paragraph as a whole is
fully justified, the last line should not be.
If nosqueeze is non-nil, that means do not change interior
whitespace.
left, right, full, center, or
none. The default value is left.
nil, a period followed by just one space
does not count as the end of a sentence, and the filling functions
avoid breaking the line at such a place.
nil, fill-paragraph calls
this function to do the work. If the function returns a non-nil
value, fill-paragraph assumes the job is done, and immediately
returns that value.
The usual use of this feature is to fill comments in programming language modes. If the function needs to fill a paragraph in the usual way, it can do so as follows:
(let ((fill-paragraph-function nil)) (fill-paragraph arg))
nil, the filling functions do not delete
newlines that have the hard text property. These "hard
newlines" act as paragraph separators.
The fill prefix follows the left margin whitespace, if any.
As a practical matter, if you are writing text for other people to
read, you should set fill-column to no more than 70. Otherwise
the line will be too long for people to read comfortably, and this can
make the text seem clumsy.
fill-column in
buffers that do not override it. This is the same as
(default-value 'fill-column).
The default value for default-fill-column is 70.
left-margin property on the text from from to
to to the value margin. If Auto Fill mode is enabled, this
command also refills the region to fit the new margin.
right-margin property on the text from from
to to to the value margin. If Auto Fill mode is enabled,
this command also refills the region to fit the new margin.
left-margin
property of the character at the start of the current line (or zero if
none), and the value of the variable left-margin.
fill-column
variable, minus the value of the right-margin property of the
character after point.
current-left-margin. If the argument n is non-nil,
move-to-left-margin moves forward n-1 lines first.
If force is non-nil, that says to fix the line's
indentation if that doesn't match the left margin value.
current-left-margin.
In no case does this function delete non-whitespace.
indent-line-function, used in Fundamental
mode, Text mode, etc. Its effect is to adjust the indentation at the
beginning of the current line to the value specified by the variable
left-margin. This may involve either inserting or deleting
whitespace.
nil, then the line won't be broken there.
Adaptive Fill mode chooses a fill prefix automatically from the text in each paragraph being filled.
nil.
It is t by default.
comment-start-skip, then it
is used--otherwise, spaces amounting to the same width are used
instead.
However, the fill prefix is never taken from a one-line paragraph if it would act as a paragraph starter on subsequent lines.
adaptive-fill-regexp does not match, with point after
the left margin of a line, and it should return the appropriate fill
prefix based on that line. If it returns nil, that means it sees
no fill prefix in that line.
Auto Fill mode is a minor mode that fills lines automatically as text is inserted. This section describes the hook used by Auto Fill mode. For a description of functions that you can call explicitly to fill and justify existing text, see section Filling.
Auto Fill mode also enables the functions that change the margins and justification style to refill portions of the text. See section Margins for Filling.
nil,
in which case nothing special is done in that case.
The value of auto-fill-function is do-auto-fill when
Auto-Fill mode is enabled. That is a function whose sole purpose is to
implement the usual strategy for breaking a line.
In older Emacs versions, this variable was named
auto-fill-hook, but since it is not called with the standard convention for hooks, it was renamed toauto-fill-functionin version 19.
auto-fill-function, if and when Auto Fill is turned on. Major
modes can set buffer-local values for this variable to alter how Auto
Fill works.
The sorting functions described in this section all rearrange text in
a buffer. This is in contrast to the function sort, which
rearranges the order of the elements of a list (see section Functions that Rearrange Lists).
The values returned by these functions are not meaningful.
To understand how sort-subr works, consider the whole accessible
portion of the buffer as being divided into disjoint pieces called
sort records. The records may or may not be contiguous, but they
must not overlap. A portion of each sort record (perhaps all of it) is
designated as the sort key. Sorting rearranges the records in order by
their sort keys.
Usually, the records are rearranged in order of ascending sort key.
If the first argument to the sort-subr function, reverse,
is non-nil, the sort records are rearranged in order of
descending sort key.
The next four arguments to sort-subr are functions that are
called to move point across a sort record. They are called many times
from within sort-subr.
sort-subr is
called. Therefore, you should usually move point to the beginning of
the buffer before calling sort-subr.
This function can indicate there are no more sort records by leaving
point at the end of the buffer.
nil value to be used as the sort key, or
return nil to indicate that the sort key is in the buffer
starting at point. In the latter case, endkeyfun is called to
find the end of the sort key.
nil and this argument is omitted (or
nil), then the sort key extends to the end of the record. There
is no need for endkeyfun if startkeyfun returns a
non-nil value.
As an example of sort-subr, here is the complete function
definition for sort-lines:
;; Note that the first two lines of doc string
;; are effectively one line when viewed by a user.
(defun sort-lines (reverse beg end)
"Sort lines in region alphabetically;\
argument means descending order.
Called from a program, there are three arguments:
REVERSE (non-nil means reverse order),\
BEG and END (region to sort).
The variable `sort-fold-case' determines\
whether alphabetic case affects
the sort order.
(interactive "P\nr")
(save-excursion
(save-restriction
(narrow-to-region beg end)
(goto-char (point-min))
(sort-subr reverse 'forward-line 'end-of-line))))
Here forward-line moves point to the start of the next record,
and end-of-line moves point to the end of record. We do not pass
the arguments startkeyfun and endkeyfun, because the entire
record is used as the sort key.
The sort-paragraphs function is very much the same, except that
its sort-subr call looks like this:
(sort-subr reverse
(function
(lambda ()
(while (and (not (eobp))
(looking-at paragraph-separate))
(forward-line 1))))
'forward-paragraph)
Markers pointing into any sort records are left with no useful
position after sort-subr returns.
nil, sort-subr and the other
buffer sorting functions ignore case when comparing strings.
Alphabetical sorting means that two sort keys are compared by comparing the first characters of each, the second characters of each, and so on. If a mismatch is found, it means that the sort keys are unequal; the sort key whose character is less at the point of first mismatch is the lesser sort key. The individual characters are compared according to their numerical character codes in the Emacs character set.
The value of the record-regexp argument specifies how to divide the buffer into sort records. At the end of each record, a search is done for this regular expression, and the text that matches it is taken as the next record. For example, the regular expression `^.+$', which matches lines with at least one character besides a newline, would make each such line into a sort record. See section Regular Expressions, for a description of the syntax and meaning of regular expressions.
The value of the key-regexp argument specifies what part of each record is the sort key. The key-regexp could match the whole record, or only a part. In the latter case, the rest of the record has no effect on the sorted order of records, but it is carried along when the record moves to its new position.
The key-regexp argument can refer to the text matched by a subexpression of record-regexp, or it can be a regular expression on its own.
If key-regexp is:
sort-regexp-fields searches for a match for the regular
expression within the record. If such a match is found, it is the sort
key. If there is no match for key-regexp within a record then
that record is ignored, which means its position in the buffer is not
changed. (The other records may move around it.)
For example, if you plan to sort all the lines in the region by the first word on each line starting with the letter `f', you should set record-regexp to `^.*$' and set key-regexp to `\<f\w*\>'. The resulting expression looks like this:
(sort-regexp-fields nil "^.*$" "\\<f\\w*\\>"
(region-beginning)
(region-end))
If you call sort-regexp-fields interactively, it prompts for
record-regexp and key-regexp in the minibuffer.
nil, the sort
is in reverse order.
nil, the sort
is in reverse order.
nil, the sort
is in reverse order.
If reverse is non-nil, the sort is in reverse order.
One unusual thing about this command is that the entire line containing position beg, and the entire line containing position end, are included in the region sorted.
Note that sort-columns uses the sort utility program,
and so cannot work properly on text containing tab characters. Use
M-x untabify to convert tabs to spaces before sorting.
The column functions convert between a character position (counting characters from the beginning of the buffer) and a column position (counting screen characters from the beginning of a line).
These functions count each character according to the number of
columns it occupies on the screen. This means control characters count
as occupying 2 or 4 columns, depending upon the value of
ctl-arrow, and tabs count as occupying a number of columns that
depends on the value of tab-width and on the column where the tab
begins. See section Usual Display Conventions.
Column number computations ignore the width of the window and the amount of horizontal scrolling. Consequently, a column value can be arbitrarily high. The first (or leftmost) column is numbered 0.
For an example of using current-column, see the description of
count-lines in section Motion by Text Lines.
If column column is beyond the end of the line, point moves to the end of the line. If column is negative, point moves to the beginning of the line.
If it is impossible to move to column column because that is in
the middle of a multicolumn character such as a tab, point moves to the
end of that character. However, if force is non-nil, and
column is in the middle of a tab, then move-to-column
converts the tab into spaces so that it can move precisely to column
column. Other multicolumn characters can cause anomalies despite
force, since there is no way to split them.
The argument force also has an effect if the line isn't long enough to reach column column; in that case, it says to add whitespace at the end of the line to reach that column.
If column is not an integer, an error is signaled.
The return value is the column number actually moved to.
The indentation functions are used to examine, move to, and change whitespace that is at the beginning of a line. Some of the functions can also change whitespace elsewhere on a line. Columns and indentation count from zero at the left margin.
This section describes the primitive functions used to count and insert indentation. The functions in the following sections use these primitives. See section Width, for related functions.
nil, then at
least that many spaces are inserted even if this requires going beyond
column. Otherwise the function does nothing if point is already
beyond column. The value is the column at which the inserted
indentation ends.
The inserted whitespace characters inherit text properties from the surrounding text (usually, from the preceding text only). See section Stickiness of Text Properties.
nil, indentation functions can insert
tabs as well as spaces. Otherwise, they insert only spaces. Setting
this variable automatically makes it buffer-local in the current buffer.
An important function of each major mode is to customize the TAB key to indent properly for the language being edited. This section describes the mechanism of the TAB key and how to control it. The functions in this section return unpredictable values.
indent-according-to-mode does no more than call this function.
In Lisp mode, the value is the symbol lisp-indent-line; in C
mode, c-indent-line; in Fortran mode, fortran-indent-line.
In Fundamental mode, Text mode, and many other modes with no standard
for indentation, the value is indent-to-left-margin (which is the
default value).
indent-line-function to
indent the current line in a way appropriate for the current major mode.
indent-line-function to indent
the current line; however, if that function is
indent-to-left-margin, insert-tab is called instead. (That
is a trivial command that inserts a tab character.)
It does indentation by calling the current indent-line-function.
In programming language modes, this is the same thing TAB does,
but in some text modes, where TAB inserts a tab,
newline-and-indent indents to the column specified by
left-margin.
This command does indentation on both lines according to the current
major mode, by calling the current value of indent-line-function.
In programming language modes, this is the same thing TAB does,
but in some text modes, where TAB inserts a tab,
reindent-then-newline-and-indent indents to the column specified
by left-margin.
This section describes commands that indent all the lines in the region. They return unpredictable values.
nil, indent-region indents each nonblank line by calling
the current mode's indentation function, the value of
indent-line-function.
If to-column is non-nil, it should be an integer
specifying the number of columns of indentation; then this function
gives each line exactly that much indentation, by either adding or
deleting whitespace.
If there is a fill prefix, indent-region indents each line
by making it start with the fill prefix.
indent-region as a short cut. It should take two arguments, the
start and end of the region. You should design the function so
that it will produce the same results as indenting the lines of the
region one by one, but presumably faster.
If the value is nil, there is no short cut, and
indent-region actually works line by line.
A short-cut function is useful in modes such as C mode and Lisp mode,
where the indent-line-function must scan from the beginning of
the function definition: applying it to each line would be quadratic in
time. The short cut can update the scan information as it moves through
the lines indenting them; this takes linear time. In a mode where
indenting a line individually is fast, there is no need for a short cut.
indent-region with a non-nil argument to-column has
a different meaning and does not use this variable.
For example, if count is 3, this command adds 3 columns of indentation to each of the lines beginning in the region specified.
In Mail mode, C-c C-y (mail-yank-original) uses
indent-rigidly to indent the text copied from the message being
replied to.
indent-rigidly, except that it doesn't alter lines
that start within strings or comments.
In addition, it doesn't alter a line if nochange-regexp matches at
the beginning of the line (if nochange-regexp is non-nil).
This section describes two commands that indent the current line based on the contents of previous lines.
If the previous nonblank line has no next indent point (i.e., none at a
great enough column position), indent-relative either does
nothing (if unindented-ok is non-nil) or calls
tab-to-tab-stop. Thus, if point is underneath and to the right
of the last column of a short line of text, this command ordinarily
moves point to the next tab stop by inserting whitespace.
The return value of indent-relative is unpredictable.
In the following example, point is at the beginning of the second line:
This line is indented twelve spaces.
-!-The quick brown fox jumped.
Evaluation of the expression (indent-relative nil) produces the
following:
This line is indented twelve spaces.
-!-The quick brown fox jumped.
In this next example, point is between the `m' and `p' of `jumped':
This line is indented twelve spaces.
The quick brown fox jum-!-ped.
Evaluation of the expression (indent-relative nil) produces the
following:
This line is indented twelve spaces.
The quick brown fox jum -!-ped.
indent-relative with t as the
unindented-ok argument. The return value is unpredictable.
If the previous nonblank line has no indent points beyond the current column, this command does nothing.
This section explains the mechanism for user-specified "tab stops" and the mechanisms that use and set them. The name "tab stops" is used because the feature is similar to that of the tab stops on a typewriter. The feature works by inserting an appropriate number of spaces and tab characters to reach the next tab stop column; it does not affect the display of tab characters in the buffer (see section Usual Display Conventions). Note that the TAB character as input uses this tab stop feature only in a few major modes, such as Text mode.
tab-stop-list. It searches the list for
an element greater than the current column number, and uses that element
as the column to indent to. It does nothing if no such element is
found.
tab-to-tab-stops. The elements should be integers in increasing
order. The tab stop columns need not be evenly spaced.
Use M-x edit-tab-stops to edit the location of tab stops interactively.
These commands, primarily for interactive use, act based on the indentation in the text.
nil.
nil.
nil.
The case change commands described here work on text in the current buffer. See section Case Conversion in Lisp, for case conversion functions that work on strings and characters. See section The Case Table, for how to customize which characters are upper or lower case and how to convert them.
nil.
If one end of the region is in the middle of a word, the part of the word within the region is treated as an entire word.
When capitalize-region is called interactively, start and
end are point and the mark, with the smallest first.
---------- Buffer: foo ---------- This is the contents of the 5th foo. ---------- Buffer: foo ---------- (capitalize-region 1 44) => nil ---------- Buffer: foo ---------- This Is The Contents Of The 5th Foo. ---------- Buffer: foo ----------
nil.
When downcase-region is called interactively, start and
end are point and the mark, with the smallest first.
nil.
When upcase-region is called interactively, start and
end are point and the mark, with the smallest first.
nil.
If point is in the middle of a word, the part of the word before point is ignored when moving forward. The rest is treated as an entire word.
When capitalize-word is called interactively, count is
set to the numeric prefix argument.
nil.
When downcase-word is called interactively, count is set
to the numeric prefix argument.
nil.
When upcase-word is called interactively, count is set to
the numeric prefix argument.
Each character position in a buffer or a string can have a text property list, much like the property list of a symbol (see section Property Lists). The properties belong to a particular character at a particular place, such as, the letter `T' at the beginning of this sentence or the first `o' in `foo'---if the same character occurs in two different places, the two occurrences generally have different properties.
Each property has a name and a value. Both of these can be any Lisp object, but the name is normally a symbol. The usual way to access the property list is to specify a name and ask what value corresponds to it.
If a character has a category property, we call it the
category of the character. It should be a symbol. The properties
of the symbol serve as defaults for the properties of the character.
Copying text between strings and buffers preserves the properties
along with the characters; this includes such diverse functions as
substring, insert, and buffer-substring.
The simplest way to examine text properties is to ask for the value of
a particular property of a particular character. For that, use
get-text-property. Use text-properties-at to get the
entire property list of a character. See section Text Property Search Functions, for
functions to examine the properties of a number of characters at once.
These functions handle both strings and buffers. Keep in mind that positions in a string start from 0, whereas positions in a buffer start from 1.
If there is no prop property strictly speaking, but the character
has a category that is a symbol, then get-text-property returns
the prop property of that symbol.
get-text-property, except that it checks
overlays first and then text properties. See section Overlays.
The argument object may be a string, a buffer, or a window. If it is a window, then the buffer displayed in that window is used for text properties and overlays, but only the overlays active for that window are considered. If object is a buffer, then all overlays in that buffer are considered, as well as text properties. If object is a string, only text properties are considered, since strings never have overlays.
nil, it defaults to the current buffer.
(setq default-text-properties '(foo 69))
;; Make sure character 1 has no properties of its own.
(set-text-properties 1 2 nil)
;; What we get, when we ask, is the default value.
(get-text-property 1 'foo)
=> 69
The primitives for changing properties apply to a specified range of
text in a buffer or string. The function set-text-properties
(see end of section) sets the entire property list of the text in that
range; more often, it is useful to add, change, or delete just certain
properties specified by name.
Since text properties are considered part of the contents of the buffer (or string), and can affect how a buffer looks on the screen, any change in buffer text properties mark the buffer as modified. Buffer text property changes are undoable also (see section Undo).
nil, it defaults to the current buffer.
nil, it defaults to the current buffer.
The argument props specifies which properties to add. It should have the form of a property list (see section Property Lists): a list whose elements include the property names followed alternately by the corresponding values.
The return value is t if the function actually changed some
property's value; nil otherwise (if props is nil or
its values agree with those in the text).
For example, here is how to set the comment and face
properties of a range of text:
(add-text-properties start end
'(comment t face highlight))
nil, it defaults to the current buffer.
The argument props specifies which properties to delete. It
should have the form of a property list (see section Property Lists): a list
whose elements are property names alternating with corresponding values.
But only the names matter--the values that accompany them are ignored.
For example, here's how to remove the face property.
(remove-text-properties start end '(face nil))
The return value is t if the function actually changed some
property's value; nil otherwise (if props is nil or
if no character in the specified text had any of those properties).
To remove all text properties from certain text, use
set-text-properties and specify nil for the new property
list.
nil, it defaults to the current buffer.
The argument props is the new property list. It should be a list whose elements are property names alternating with corresponding values.
After set-text-properties returns, all the characters in the
specified range have identical properties.
If props is nil, the effect is to get rid of all properties
from the specified range of text. Here's an example:
(set-text-properties start end nil)
See also the function buffer-substring-no-properties
(see section Examining Buffer Contents) which copies text from the buffer
but does not copy its properties.
In typical use of text properties, most of the time several or many consecutive characters have the same value for a property. Rather than writing your programs to examine characters one by one, it is much faster to process chunks of text that have the same property value.
Here are functions you can use to do this. They use eq for
comparing property values. In all cases, object defaults to the
current buffer.
For high performance, it's very important to use the limit argument to these functions, especially the ones that search for a single property--otherwise, they may spend a long time scanning to the end of the buffer, if the property you are interested in does not change.
These functions do not move point; instead, they return a position (or
nil). Remember that a position is always between two characters;
the position returned by these functions is between two characters with
different properties.
If limit is non-nil, then the scan ends at position
limit. If there is no property change before that point,
next-property-change returns limit.
The value is nil if the properties remain unchanged all the way
to the end of object and limit is nil. If the value
is non-nil, it is a position greater than or equal to pos.
The value equals pos only when limit equals pos.
Here is an example of how to scan the buffer by chunks of text within which all properties are constant:
(while (not (eobp))
(let ((plist (text-properties-at (point)))
(next-change
(or (next-property-change (point) (current-buffer))
(point-max))))
Process text from point to next-change...
(goto-char next-change)))
If limit is non-nil, then the scan ends at position
limit. If there is no property change before that point,
next-single-property-change returns limit.
The value is nil if the property remains unchanged all the way to
the end of object and limit is nil. If the value is
non-nil, it is a position greater than or equal to pos; it
equals pos only if limit equals pos.
next-property-change, but scans back from pos
instead of forward. If the value is non-nil, it is a position
less than or equal to pos; it equals pos only if limit
equals pos.
next-single-property-change, but scans back from
pos instead of forward. If the value is non-nil, it is a
position less than or equal to pos; it equals pos only if
limit equals pos.
next-property-change except that it considers
overlay properties as well as text properties. There is no object
operand because this function operates only on the current buffer. It
returns the next address at which either kind of property changes.
next-char-property-change, but scans back from
position instead of forward.
nil if at least one character between
start and end has a property prop whose value is
value. More precisely, it returns the position of the first such
character. Otherwise, it returns nil.
The optional fifth argument, object, specifies the string or buffer to scan. Positions are relative to object. The default for object is the current buffer.
nil if at least one character between
start and end does not have a property prop with value
value. More precisely, it returns the position of the first such
character. Otherwise, it returns nil.
The optional fifth argument, object, specifies the string or buffer to scan. Positions are relative to object. The default for object is the current buffer.
Here is a table of text property names that have special built-in meanings. The following sections list a few additional special property names that control filling and property inheritance. All other names have no standard meaning, and you can use them as you like.
category
category property, we call it the
category of the character. It should be a symbol. The properties
of the symbol serve as defaults for the properties of the character.
face
face to control the font and color of
text. Its value is a face name or a list of face names. See section Faces,
for more information.
If the property value is a list, elements may also have the form
(foreground-color . color-name) or (background-color
. color-name). These elements specify just the foreground color
or just the background color; therefore, there is no need to create a
face for each color that you want to use.
See section Font Lock Mode, for information on how to update face
properties automatically based on the contents of the text.
mouse-face
mouse-face is used instead of face when the
mouse is on or near the character. For this purpose, "near" means
that all text between the character and where the mouse is have the same
mouse-face property value.
local-map
local-map property. The property's value for the
character after point, if non-nil, is used for key lookup instead
of the buffer's local map. If the property value is a symbol, the
symbol's function definition is used as the keymap. See section Active Keymaps.
syntax-table
syntax-table property overrides what the syntax table says
about this particular character. See section Syntax Properties.
read-only
read-only, then modifying that
character is not allowed. Any command that would do so gets an error.
Insertion next to a read-only character is an error if inserting
ordinary text there would inherit the read-only property due to
stickiness. Thus, you can control permission to insert next to
read-only text by controlling the stickiness. See section Stickiness of Text Properties.
Since changing properties counts as modifying the buffer, it is not
possible to remove a read-only property unless you know the
special trick: bind inhibit-read-only to a non-nil value
and then remove the property. See section Read-Only Buffers.
invisible
nil invisible property can make a character invisible
on the screen. See section Invisible Text, for details.
intangible
nil
intangible properties, then you cannot place point between them.
If you try to move point forward into the group, point actually moves to
the end of the group. If you try to move point backward into the group,
point actually moves to the start of the group.
When the variable inhibit-point-motion-hooks is non-nil,
the intangible property is ignored.
modification-hooks
modification-hooks, then its
value should be a list of functions; modifying that character calls all
of those functions. Each function receives two arguments: the beginning
and end of the part of the buffer being modified. Note that if a
particular modification hook function appears on several characters
being modified by a single primitive, you can't predict how many times
the function will be called.
insert-in-front-hooks
insert-behind-hooks
insert-in-front-hooks property of the following
character and in the insert-behind-hooks property of the
preceding character. These functions receive two arguments, the
beginning and end of the inserted text. The functions are called
after the actual insertion takes place.
See also section Change Hooks, for other hooks that are called
when you change text in a buffer.
point-entered
point-left
point-entered and point-left
record hook functions that report motion of point. Each time point
moves, Emacs compares these two property values:
point-left property of the character after the old location,
and
point-entered property of the character after the new
location.
nil)
with two arguments: the old value of point, and the new one.
The same comparison is made for the characters before the old and new
locations. The result may be to execute two point-left functions
(which may be the same function) and/or two point-entered
functions (which may be the same function). In any case, all the
point-left functions are called first, followed by all the
point-entered functions.
It is possible using char-after to examine characters at various
positions without moving point to those positions. Only an actual
change in the value of point runs these hook functions.
nil, point-left and
point-entered hooks are not run, and the intangible
property has no effect. Do not set this variable globally; bind it with
let.
These text properties affect the behavior of the fill commands. They are used for representing formatted text. See section Filling, and section Margins for Filling.
hard
use-hard-newlines is non-nil.
right-margin
left-margin
justification
Self-inserting characters normally take on the same properties as the preceding character. This is called inheritance of properties.
In a Lisp program, you can do insertion with inheritance or without,
depending on your choice of insertion primitive. The ordinary text
insertion functions such as insert do not inherit any properties.
They insert text with precisely the properties of the string being
inserted, and no others. This is correct for programs that copy text
from one context to another--for example, into or out of the kill ring.
To insert with inheritance, use the special primitives described in this
section. Self-inserting characters inherit properties because they work
using these primitives.
When you do insertion with inheritance, which properties are
inherited depends on two specific properties: front-sticky and
rear-nonsticky.
Insertion after a character inherits those of its properties that are rear-sticky. Insertion before a character inherits those of its properties that are front-sticky. By default, a text property is rear-sticky but not front-sticky. Thus, the default is to inherit all the properties of the preceding character, and nothing from the following character. You can request different behavior by specifying the stickiness of certain properties.
If a character's front-sticky property is t, then all
its properties are front-sticky. If the front-sticky property is
a list, then the sticky properties of the character are those whose
names are in the list. For example, if a character has a
front-sticky property whose value is (face read-only),
then insertion before the character can inherit its face property
and its read-only property, but no others.
The rear-nonsticky works the opposite way. Every property is
rear-sticky by default, so the rear-nonsticky property says which
properties are not rear-sticky. If a character's
rear-nonsticky property is t, then none of its properties
are rear-sticky. If the rear-nonsticky property is a list,
properties are rear-sticky unless their names are in the list.
When you insert text with inheritance, it inherits all the rear-sticky properties of the preceding character, and all the front-sticky properties of the following character. The previous character's properties take precedence when both sides offer different sticky values for the same property.
Here are the functions that insert text with inheritance of properties:
insert,
but inherit any sticky properties from the adjoining text.
insert-before-markers, but inherit any sticky properties from the
adjoining text.
See section Inserting Text, for the ordinary insertion functions which do not inherit.
You can save text properties in files (along with the text itself), and restore the same text properties when visiting or inserting the files, using these two hooks:
write-region to
run to encode text properties in some fashion as annotations to the text
being written in the file. See section Writing to Files.
Each function in the list is called with two arguments: the start and end of the region to be written. These functions should not alter the contents of the buffer. Instead, they should return lists indicating annotations to write in the file in addition to the text in the buffer.
Each function should return a list of elements of the form
(position . string), where position is an
integer specifying the relative position within the text to be written,
and string is the annotation to add there.
Each list returned by one of these functions must be already sorted in
increasing order by position. If there is more than one function,
write-region merges the lists destructively into one sorted list.
When write-region actually writes the text from the buffer to the
file, it intermixes the specified annotations at the corresponding
positions. All this takes place without modifying the buffer.
insert-file-contents
to call after inserting a file's contents. These functions should scan
the inserted text for annotations, and convert them to the text
properties they stand for.
Each function receives one argument, the length of the inserted text; point indicates the start of that text. The function should scan that text for annotations, delete them, and create the text properties that the annotations specify. The function should return the updated length of the inserted text, as it stands after those changes. The value returned by one function becomes the argument to the next function.
These functions should always return with point at the beginning of the inserted text.
The intended use of after-insert-file-functions is for converting
some sort of textual annotations into actual text properties. But other
uses may be possible.
We invite users to write Lisp programs to store and retrieve text properties in files, using these hooks, and thus to experiment with various data formats and find good ones. Eventually we hope users will produce good, general extensions we can install in Emacs.
We suggest not trying to handle arbitrary Lisp objects as text property names or values--because a program that general is probably difficult to write, and slow. Instead, choose a set of possible data types that are reasonably flexible, and not too hard to encode.
See section File Format Conversion, for a related feature.
Instead of computing text properties for all the text in the buffer, you can arrange to compute the text properties for parts of the text when and if something depends on them.
The primitive that extracts text from the buffer along with its
properties is buffer-substring. Before examining the properties,
this function runs the abnormal hook buffer-access-fontify-functions.
buffer-substring copies the text and text properties for a
portion of the buffer, it calls all the functions in this list. Each of
the functions receives two arguments that specify the range of the
buffer being accessed. (The buffer itself is always the current
buffer.)
The function buffer-substring-no-properties does not call these
functions, since it ignores text properties anyway.
In order to prevent the hook functions from being called more than
once for the same part of the buffer, you can use the variable
buffer-access-fontified-property.
nil, it is a symbol which is used
as a text property name. A non-nil value for that text property
means, "the other text properties for this character have already been
computed."
If all the characters in the range specified for buffer-substring
have a non-nil value for this property, buffer-substring
does not call the buffer-access-fontify-functions functions. It
assumes these characters already have the right text properties, and
just copies the properties they already have.
The normal way to use this feature is that the
buffer-access-fontify-functions functions add this property, as
well as others, to the characters they operate on. That way, they avoid
being called over and over for the same text.
There are two ways to set up clickable text in a buffer. There are typically two parts of this: to make the text highlight when the mouse is over it, and to make a mouse button do something when you click it on that part of the text.
Highlighting is done with the mouse-face text property.
Here is an example of how Dired does it:
(condition-case nil
(if (dired-move-to-filename)
(put-text-property (point)
(save-excursion
(dired-move-to-end-of-filename)
(point))
'mouse-face 'highlight))
(error nil))
The first two arguments to put-text-property specify the
beginning and end of the text.
The usual way to make the mouse do something when you click it
on this text is to define mouse-2 in the major mode's
keymap. The job of checking whether the click was on clickable text
is done by the command definition. Here is how Dired does it:
(defun dired-mouse-find-file-other-window (event)
"In dired, visit the file or directory name you click on."
(interactive "e")
(let (file)
(save-excursion
(set-buffer (window-buffer (posn-window (event-end event))))
(save-excursion
(goto-char (posn-point (event-end event)))
(setq file (dired-get-filename))))
(select-window (posn-window (event-end event)))
(find-file-other-window (file-name-sans-versions file t))))
The reason for the outer save-excursion construct is to avoid
changing the current buffer; the reason for the inner one is to avoid
permanently altering point in the buffer you click on. In this case,
Dired uses the function dired-get-filename to determine which
file to visit, based on the position found in the event.
Instead of defining a mouse command for the major mode, you can define
a key binding for the clickable text itself, using the local-map
text property:
(let ((map (make-sparse-keymap)))
(define-key-binding map [mouse-2] 'operate-this-button)
(put-text-property (point)
(save-excursion
(dired-move-to-end-of-filename)
(point))
'local-map map))
This method makes it possible to define different commands for various clickable pieces of text. Also, the major mode definition (or the global definition) remains available for the rest of the text in the buffer.
Some editors that support adding attributes to text in the buffer do so by letting the user specify "intervals" within the text, and adding the properties to the intervals. Those editors permit the user or the programmer to determine where individual intervals start and end. We deliberately provided a different sort of interface in Emacs Lisp to avoid certain paradoxical behavior associated with text modification.
If the actual subdivision into intervals is meaningful, that means you can distinguish between a buffer that is just one interval with a certain property, and a buffer containing the same text subdivided into two intervals, both of which have that property.
Suppose you take the buffer with just one interval and kill part of the text. The text remaining in the buffer is one interval, and the copy in the kill ring (and the undo list) becomes a separate interval. Then if you yank back the killed text, you get two intervals with the same properties. Thus, editing does not preserve the distinction between one interval and two.
Suppose we "fix" this problem by coalescing the two intervals when the text is inserted. That works fine if the buffer originally was a single interval. But suppose instead that we have two adjacent intervals with the same properties, and we kill the text of one interval and yank it back. The same interval-coalescence feature that rescues the other case causes trouble in this one: after yanking, we have just one interval. One again, editing does not preserve the distinction between one interval and two.
Insertion of text at the border between intervals also raises questions that have no satisfactory answer.
However, it is easy to arrange for editing to behave consistently for questions of the form, "What are the properties of this character?" So we have decided these are the only questions that make sense; we have not implemented asking questions about where intervals start or end.
In practice, you can usually use the text property search functions in place of explicit interval boundaries. You can think of them as finding the boundaries of intervals, assuming that intervals are always coalesced whenever possible. See section Text Property Search Functions.
Emacs also provides explicit intervals as a presentation feature; see section Overlays.
The following functions replace characters within a specified region based on their character codes.
If noundo is non-nil, then subst-char-in-region does
not record the change for undo and does not mark the buffer as modified.
This feature is used for controlling selective display (see section Selective Display).
subst-char-in-region does not move point and returns
nil.
---------- Buffer: foo ----------
This is the contents of the buffer before.
---------- Buffer: foo ----------
(subst-char-in-region 1 20 ?i ?X)
=> nil
---------- Buffer: foo ----------
ThXs Xs the contents of the buffer before.
---------- Buffer: foo ----------
The translation table table is a string; (aref table
ochar) gives the translated character corresponding to
ochar. If the length of table is less than 256, any
characters with codes larger than the length of table are not
altered by the translation.
The return value of translate-region is the number of
characters that were actually changed by the translation. This does
not count characters that were mapped into themselves in the
translation table.
A register is a sort of variable used in Emacs editing that can hold a variety of different kinds of values. Each register is named by a single character. All ASCII characters and their meta variants (but with the exception of C-g) can be used to name registers. Thus, there are 255 possible registers. A register is designated in Emacs Lisp by the character that is its name.
(name .
contents). Normally, there is one element for each Emacs
register that has been used.
The object name is a character (an integer) identifying the register.
The contents of a register can have several possible types:
insert-register finds a number
in the register, it converts the number to decimal.
(window-configuration position)
(frame-configuration position)
The functions in this section return unpredictable values unless otherwise stated.
nil if it has no contents.
Normally, this command puts point before the inserted text, and the
mark after it. However, if the optional second argument beforep
is non-nil, it puts the mark before and point after.
You can pass a non-nil second argument beforep to this
function interactively by supplying any prefix argument.
If the register contains a rectangle, then the rectangle is inserted with its upper left corner at point. This means that text is inserted in the current line and underneath it on successive lines.
If the register contains something other than saved text (a string) or a rectangle (a list), currently useless things happen. This may be changed in the future.
This subroutine is used by the transposition commands.
Normally, transpose-regions relocates markers with the transposed
text; a marker previously positioned within one of the two transposed
portions moves along with that portion, thus remaining between the same
two characters in their new position. However, if leave-markers
is non-nil, transpose-regions does not do this--it leaves
all markers unrelocated.
These hook variables let you arrange to take notice of all changes in all buffers (or in a particular buffer, if you make them buffer-local). See also section Properties with Special Meanings, for how to detect changes to specific parts of the text.
The functions you use in these hooks should save and restore the match data if they do anything that uses regular expressions; otherwise, they will interfere in bizarre ways with the editing operations that call them.
The length of the old text is the difference between the buffer positions before and after that text as it was before the change. As for the changed text, its length is simply the difference between the first two arguments.
If a program makes several text changes in the same area of the buffer,
using the macro combine-after-change-calls around that part of
the program can make it run considerably faster when after-change hooks
are in use. When the after-change hooks are ultimately called, the
arguments specify a portion of the buffer including all of the changes
made within the combine-after-change-calls body.
Warning: You must not alter the values of
after-change-functions and after-change-function within
the body of a combine-after-change-calls form.
Note: If the changes you combine occur in widely scattered parts of the buffer, this will still work, but it is not advisable, because it may lead to inefficient behavior for some change hook functions.
nil for no function). It is called just like
the functions in before-change-functions.
nil for no function). It is called just like the functions in
after-change-functions.
The four variables above are temporarily bound to nil during the
time that any of these functions is running. This means that if one of
these functions changes the buffer, that change won't run these
functions. If you do want a hook function to make changes that run
these functions, make it bind these variables back to their usual
values.
One inconvenient result of this protective feature is that you cannot
have a function in after-change-functions or
before-change-functions which changes the value of that variable.
But that's not a real limitation. If you want those functions to change
the list of functions to run, simply add one fixed function to the hook,
and code that function to look in another variable for other functions
to call. Here is an example:
(setq my-own-after-change-functions nil)
(defun indirect-after-change-function (beg end len)
(let ((list my-own-after-change-functions))
(while list
(funcall (car list) beg end len)
(setq list (cdr list)))))
(add-hooks 'after-change-functions
'indirect-after-change-function)
This chapter covers the special issues relating to non-ASCII characters and how they are stored in strings and buffers.
Emacs has two text representations---two ways to represent text in a string or buffer. These are called unibyte and multibyte. Each string, and each buffer, uses one of these two representations. For most purposes, you can ignore the issue of representations, because Emacs converts text between them as appropriate. Occasionally in Lisp programming you will need to pay attention to the difference.
In unibyte representation, each character occupies one byte and
therefore the possible character codes range from 0 to 255. Codes 0
through 127 are ASCII characters; the codes from 128 through 255
are used for one non-ASCII character set (you can choose which
character set by setting the variable nonascii-insert-offset).
In multibyte representation, a character may occupy more than one byte, and as a result, the full range of Emacs character codes can be stored. The first byte of a multibyte character is always in the range 128 through 159 (octal 0200 through 0237). These values are called leading codes. The second and subsequent bytes of a multibyte character are always in the range 160 through 255 (octal 0240 through 0377); these values are trailing codes.
In a buffer, the buffer-local value of the variable
enable-multibyte-characters specifies the representation used.
The representation for a string is determined based on the string
contents when the string is constructed.
nil, the buffer contains multibyte text; otherwise,
it contains unibyte text.
You cannot set this variable directly; instead, use the function
set-buffer-multibyte to change a buffer's representation.
(default-value
'enable-multibyte-characters), and setting this variable changes that
default value. Setting the local binding of
enable-multibyte-characters in a specific buffer is not allowed,
but changing the default value is supported, and it is a reasonable
thing to do, because it has no effect on existing buffers.
The `--unibyte' command line option does its job by setting the
default value to nil early in startup.
t if string contains multibyte characters.
Emacs can convert unibyte text to multibyte; it can also convert multibyte text to unibyte, though this conversion loses information. In general these conversions happen when inserting text into a buffer, or when putting text from several strings together in one string. You can also explicitly convert a string's contents to either representation.
Emacs chooses the representation for a string based on the text that it is constructed from. The general rule is to convert unibyte text to multibyte text when combining it with other multibyte text, because the multibyte representation is more general and can hold whatever characters the unibyte text has.
When inserting text into a buffer, Emacs converts the text to the
buffer's representation, as specified by
enable-multibyte-characters in that buffer. In particular, when
you insert multibyte text into a unibyte buffer, Emacs converts the text
to unibyte, even though this conversion cannot in general preserve all
the characters that might be in the multibyte text. The other natural
alternative, to convert the buffer contents to multibyte, is not
acceptable because the buffer's representation is a choice made by the
user that cannot be overridden automatically.
Converting unibyte text to multibyte text leaves ASCII characters
unchanged, and likewise 128 through 159. It converts the non-ASCII
codes 160 through 255 by adding the value nonascii-insert-offset
to each character code. By setting this variable, you specify which
character set the unibyte characters correspond to (see section Character Sets). For example, if nonascii-insert-offset is 2048, which is
(- (make-char 'latin-iso8859-1) 128), then the unibyte
non-ASCII characters correspond to Latin 1. If it is 2688, which
is (- (make-char 'greek-iso8859-7) 128), then they correspond to
Greek letters.
Converting multibyte text to unibyte is simpler: it performs
logical-and of each character code with 255. If
nonascii-insert-offset has a reasonable value, corresponding to
the beginning of some character set, this conversion is the inverse of
the other: converting unibyte text to multibyte and back to unibyte
reproduces the original unibyte text.
self-insert-command inserts a character in the unibyte
non-ASCII range, 128 through 255. However, the function
insert-char does not perform this conversion.
The right value to use to select character set cs is (-
(make-char cs) 128). If the value of
nonascii-insert-offset is zero, then conversion actually uses the
value for the Latin 1 character set, rather than zero.
nonascii-insert-offset. You can use it to specify independently
how to translate each code in the range of 128 through 255 into a
multibyte character. The value should be a vector, or nil.
If this is non-nil, it overrides nonascii-insert-offset.
Sometimes it is useful to examine an existing buffer or string as multibyte when it was unibyte, or vice versa.
nil, the buffer becomes multibyte. If multibyte
is nil, the buffer becomes unibyte.
This function leaves the buffer contents unchanged when viewed as a sequence of bytes. As a consequence, it can change the contents viewed as characters; a sequence of two bytes which is treated as one character in multibyte representation will count as two characters in unibyte representation.
This function sets enable-multibyte-characters to record which
representation is in use. It also adjusts various data in the buffer
(including overlays, text properties and markers) so that they cover the
same text as they did before.
If string is unibyte already, then the value is string itself.
If string is multibyte already, then the value is string itself.
The unibyte and multibyte text representations use different character codes. The valid character codes for unibyte representation range from 0 to 255--the values that can fit in one byte. The valid character codes for multibyte representation range from 0 to 524287, but not all values in that range are valid. In particular, the values 128 through 255 are not legitimate in multibyte text (though they can occur in "raw bytes"; see section Explicit Encoding and Decoding). Only the ASCII codes 0 through 127 are fully legitimate in both representations.
t if charcode is valid for either one of the two
text representations.
(char-valid-p 65)
=> t
(char-valid-p 256)
=> nil
(char-valid-p 2248)
=> t
Emacs classifies characters into various character sets, each of which has a name which is a symbol. Each character belongs to one and only one character set.
In general, there is one character set for each distinct script. For
example, latin-iso8859-1 is one character set,
greek-iso8859-7 is another, and ascii is another. An
Emacs character set can hold at most 9025 characters; therefore, in some
cases, characters that would logically be grouped together are split
into several character sets. For example, one set of Chinese
characters, generally known as Big 5, is divided into two Emacs
character sets, chinese-big5-1 and chinese-big5-2.
t if object is a character set name symbol,
nil otherwise.
In multibyte representation, each character occupies one or more bytes. Each character set has an introduction sequence, which is normally one or two bytes long. (Exception: the ASCII character set has a zero-length introduction sequence.) The introduction sequence is the beginning of the byte sequence for any character in the character set. The rest of the character's bytes distinguish it from the other characters in the same character set. Depending on the character set, there are either one or two distinguishing bytes; the number of such bytes is called the dimension of the character set.
This is the simplest way to determine the byte length of a character set's introduction sequence:
(- (char-bytes (make-char charset)) (charset-dimension charset))
The functions in this section convert between characters and the byte values used to represent them. For most purposes, there is no need to be concerned with the sequence of bytes used to represent a character, because Emacs translates automatically when necessary.
(char-bytes 2248)
=> 2
(char-bytes 65)
=> 1
(char-bytes 192)
=> 1
The reason this function can give correct results for both multibyte and unibyte representations is that the non-ASCII character codes used in those two representations do not overlap.
(split-char 2248)
=> (latin-iso8859-1 72)
(split-char 65)
=> (ascii 65)
Unibyte non-ASCII characters are considered as part of
the ascii character set:
(split-char 192)
=> (ascii 192)
split-char. Normally, you should specify either one or two
byte-values, according to the dimension of charset. For
example,
(make-char 'latin-iso8859-1 72)
=> 2248
If you call make-char with no byte-values, the result is
a generic character which stands for charset. A generic
character is an integer, but it is not valid for insertion in the
buffer as a character. It can be used in char-table-range to
refer to the whole character set (see section Char-Tables).
char-valid-p returns nil for generic characters.
For example:
(make-char 'latin-iso8859-1)
=> 2176
(char-valid-p 2176)
=> nil
(split-char 2176)
=> (latin-iso8859-1 0)
Sometimes it is useful to find out which character sets appear in a part of a buffer or a string. One use for this is in determining which coding systems (see section Coding Systems) are capable of representing all of the text in question.
The optional argument translation specifies a translation table to
be used in scanning the text (see section Translation of Characters). If it
is non-nil, then each character in the region is translated
through this table, and the value returned describes the translated
characters instead of the characters actually in the buffer.
The optional argument translation specifies a
translation table; see find-charset-region, above.
A translation table specifies a mapping of characters into characters. These tables are used in encoding and decoding, and for other purposes. Some coding systems specify their own particular translation tables; there are also default translation tables which apply to all other coding systems.
(from
. to); this says to translate the character from into
to.
You can also map one whole character set into another character set with the same dimension. To do this, you specify a generic character (which designates a character set) for from (see section Splitting Characters). In this case, to should also be a generic character, for another character set of the same dimension. Then the translation table translates each character of from's character set into the corresponding character of to's character set.
In decoding, the translation table's translations are applied to the
characters that result from ordinary decoding. If a coding system has
property character-translation-table-for-decode, that specifies
the translation table to use. Otherwise, if
standard-character-translation-table-for-decode is
non-nil, decoding uses that table.
In encoding, the translation table's translations are applied to the
characters in the buffer, and the result of translation is actually
encoded. If a coding system has property
character-translation-table-for-encode, that specifies the
translation table to use. Otherwise the variable
standard-character-translation-table-for-encode specifies the
translation table.
When Emacs reads or writes a file, and when Emacs sends text to a subprocess or receives text from a subprocess, it normally performs character code conversion and end-of-line conversion as specified by a particular coding system.
Character code conversion involves conversion between the encoding used inside Emacs and some other encoding. Emacs supports many different encodings, in that it can convert to and from them. For example, it can convert text to or from encodings such as Latin 1, Latin 2, Latin 3, Latin 4, Latin 5, and several variants of ISO 2022. In some cases, Emacs supports several alternative encodings for the same characters; for example, there are three coding systems for the Cyrillic (Russian) alphabet: ISO, Alternativnyj, and KOI8.
Most coding systems specify a particular character code for conversion, but some of them leave this unspecified--to be chosen heuristically based on the data.
End of line conversion handles three different conventions used on various systems for representing end of line in files. The Unix convention is to use the linefeed character (also called newline). The DOS convention is to use the two character sequence, carriage-return linefeed, at the end of a line. The Mac convention is to use just carriage-return.
Base coding systems such as latin-1 leave the end-of-line
conversion unspecified, to be chosen based on the data. Variant
coding systems such as latin-1-unix, latin-1-dos and
latin-1-mac specify the end-of-line conversion explicitly as
well. Most base coding systems have three corresponding variants whose
names are formed by adding `-unix', `-dos' and `-mac'.
The coding system raw-text is special in that it prevents
character code conversion, and causes the buffer visited with that
coding system to be a unibyte buffer. It does not specify the
end-of-line conversion, allowing that to be determined as usual by the
data, and has the usual three variants which specify the end-of-line
conversion. no-conversion is equivalent to raw-text-unix:
it specifies no conversion of either character codes or end-of-line.
The coding system emacs-mule specifies that the data is
represented in the internal Emacs encoding. This is like
raw-text in that no code conversion happens, but different in
that the result is multibyte data.
mime-charset.
That property's value is the name used in MIME for the character coding
which this coding system can read and write. Examples:
(coding-system-get 'iso-latin-1 'mime-charset)
=> iso-8859-1
(coding-system-get 'iso-2022-cn 'mime-charset)
=> iso-2022-cn
(coding-system-get 'cyrillic-koi8 'mime-charset)
=> koi8-r
The value of the mime-charset property is also defined
as an alias for the coding system.
The principal purpose of coding systems is for use in reading and
writing files. The function insert-file-contents uses
a coding system for decoding the file data, and write-region
uses one to encode the buffer contents.
You can specify the coding system to use either explicitly
(see section Specifying a Coding System for One Operation), or implicitly using the defaulting
mechanism (see section Default Coding Systems). But these methods may not
completely specify what to do. For example, they may choose a coding
system such as undefined which leaves the character code
conversion to be determined from the data. In these cases, the I/O
operation finishes the job of choosing a coding system. Very often
you will want to find out afterwards which coding system was chosen.
write-region. When those operations ask the
user to specify a different coding system,
buffer-file-coding-system is updated to the coding system
specified.
write-region. When saving the buffer asks the
user to specify a different coding system, and
save-buffer-coding-system was used, then it is updated to the
coding system that was specified.
Warning: Since receiving subprocess output sets this variable, it can change whenever Emacs waits; therefore, you should use copy the value shortly after the function call which stores the value you are interested in.
The variable selection-coding-system specifies how to encode
selections for the window system. See section Window System Selections.
Here are Lisp facilities for working with coding systems;
nil, the value includes only the
base coding systems. Otherwise, it includes variant coding systems as well.
t if object is a coding system
name.
coding-system-error.
eol-type.
eol-type should be unix, dos, mac, or
nil. If it is nil, the returned coding system determines
the end-of-line conversion from the data.
nil, it returns
undecided, or one of its variants according to eol-coding.
If the text contains no multibyte characters, the function returns the
list (undecided).
(undecided).
Normally this function returns a list of coding systems that could
handle decoding the text that was scanned. They are listed in order of
decreasing priority. But if highest is non-nil, then the
return value is just one coding system, the one that is highest in
priority.
If the region contains only ASCII characters, the value
is undecided or (undecided).
detect-coding-region except that it
operates on the contents of string instead of bytes in the buffer.
See section Process Information, for how to examine or set the coding systems used for I/O to a subprocess.
The optional argument preferred-coding-system specifies a coding
system to try first. If that one can handle the text in the specified
region, then it is used. If this argument is omitted, the current
buffer's value of buffer-file-coding-system is tried first.
If the region contains some multibyte characters that the preferred coding system cannot encode, this function asks the user to choose from a list of coding systems which can encode the text, and returns the user's choice.
One other kludgy feature: if from is a string, the string is the target text, and to is ignored.
Here are two functions you can use to let the user specify a coding system, with completion. See section Completion.
This section describes variables that specify the default coding system for certain files or when running certain subprograms, and the function that I/O operations use to access them.
The idea of these variables is that you set them once and for all to the
defaults you want, and then do not change them again. To specify a
particular coding system for a particular operation in a Lisp program,
don't change these variables; instead, override them using
coding-system-for-read and coding-system-for-write
(see section Specifying a Coding System for One Operation).
(pattern . coding), where pattern is a regular
expression that matches certain file names. The element applies to file
names that match pattern.
The CDR of the element, coding, should be either a coding system, a cons cell containing two coding systems, or a function symbol. If val is a coding system, that coding system is used for both reading the file and writing it. If val is a cons cell containing two coding systems, its CAR specifies the coding system for decoding, and its CDR specifies the coding system for encoding.
If val is a function symbol, the function must return a coding system or a cons cell containing two coding systems. This value is used as described above.
file-coding-system-alist, except that pattern is
matched against the program name used to start the subprocess. The coding
system or systems specified in this alist are used to initialize the
coding systems used for I/O to the subprocess, but you can specify
other coding systems later using set-process-coding-system.
Warning: Coding systems such as undecided which
determine the coding system from the data do not work entirely reliably
with asynchronous subprocess output. This is because Emacs handles
asynchronous subprocess output in batches, as it arrives. If the coding
system leaves the character code conversion unspecified, or leaves the
end-of-line conversion unspecified, Emacs must try to detect the proper
conversion from one batch at a time, and this does not always work.
Therefore, with an asynchronous subprocess, if at all possible, use a
coding system which determines both the character code conversion and
the end of line conversion--that is, one like latin-1-unix,
rather than undecided or latin-1.
file-coding-system-alist,
with the difference that the pattern in an element may be either a
port number or a regular expression. If it is a regular expression, it
is matched against the network service name used to open the network
stream.
The value should be a cons cell of the form (input-coding
. output-coding). Here input-coding applies to input from
the subprocess, and output-coding applies to output to it.
(decoding-system encoding-system)
The first element, decoding-system, is the coding system to use for decoding (in case operation does decoding), and encoding-system is the coding system for encoding (in case operation does encoding).
The argument operation should be an Emacs I/O primitive:
insert-file-contents, write-region, call-process,
call-process-region, start-process, or
open-network-stream.
The remaining arguments should be the same arguments that might be given
to that I/O primitive. Depending on which primitive, one of those
arguments is selected as the target. For example, if
operation does file I/O, whichever argument specifies the file
name is the target. For subprocess primitives, the process name is the
target. For open-network-stream, the target is the service name
or port number.
This function looks up the target in file-coding-system-alist,
process-coding-system-alist, or
network-coding-system-alist, depending on operation.
See section Default Coding Systems.
You can specify the coding system for a specific operation by binding
the variables coding-system-for-read and/or
coding-system-for-write.
nil, it specifies the coding system to
use for reading a file, or for input from a synchronous subprocess.
It also applies to any asynchronous subprocess or network stream, but in
a different way: the value of coding-system-for-read when you
start the subprocess or open the network stream specifies the input
decoding method for that subprocess or network stream. It remains in
use for that subprocess or network stream unless and until overridden.
The right way to use this variable is to bind it with let for a
specific I/O operation. Its global value is normally nil, and
you should not globally set it to any other value. Here is an example
of the right way to use the variable:
;; Read the file with no character code conversion. ;; Assume CRLF represents end-of-line. (let ((coding-system-for-write 'emacs-mule-dos)) (insert-file-contents filename))
When its value is non-nil, coding-system-for-read takes
precedence over all other methods of specifying a coding system to use for
input, including file-coding-system-alist,
process-coding-system-alist and
network-coding-system-alist.
coding-system-for-read, except that it
applies to output rather than input. It affects writing to files,
subprocesses, and net connections.
When a single operation does both input and output, as do
call-process-region and start-process, both
coding-system-for-read and coding-system-for-write
affect it.
nil, no end-of-line conversion is done,
no matter which coding system is specified. This applies to all the
Emacs I/O and subprocess primitives, and to the explicit encoding and
decoding functions (see section Explicit Encoding and Decoding).
All the operations that transfer text in and out of Emacs have the ability to use a coding system to encode or decode the text. You can also explicitly encode and decode text using the functions in this section.
The result of encoding, and the input to decoding, are not ordinary
text. They are "raw bytes"---bytes that represent text in the same
way that an external file would. When a buffer contains raw bytes, it
is most natural to mark that buffer as using unibyte representation,
using set-buffer-multibyte (see section Selecting a Representation),
but this is not required. If the buffer's contents are only temporarily
raw, leave the buffer multibyte, which will be correct after you decode
them.
The usual way to get raw bytes in a buffer, for explicit decoding, is
to read them from a file with insert-file-contents-literally
(see section Reading from Files) or specify a non-nil rawfile
argument when visiting a file with find-file-noselect.
The usual way to use the raw bytes that result from explicitly
encoding text is to copy them to a file or process--for example, to
write them with write-region (see section Writing to Files), and
suppress encoding for that write-region call by binding
coding-system-for-write to no-conversion.
Raw bytes sometimes contain overlong byte-sequences that look like a proper multibyte character plus extra bytes containing trailing codes. For most purposes, Emacs treats such a sequence in a buffer or string as a single character, and if you look at its character code, you get the value that corresponds to the multibyte character sequence--the extra bytes are disregarded. This behavior is not quite clean, but raw bytes are used only in limited places in Emacs, so as a practical matter problems can be avoided.
Emacs can decode keyboard input using a coding system, and encode
terminal output. This is useful for terminals that transmit or display
text using a particular encoding such as Latin-1. Emacs does not set
last-coding-system-used for encoding or decoding for the
terminal.
nil if no coding system is to be used.
nil,
that means do not decode keyboard input.
nil for no encoding.
nil,
that means do not encode terminal output.
Emacs on MS-DOS and on MS-Windows recognizes certain file names as text files or binary files. By "binary file" we mean a file of literal byte values that are not necessary meant to be characters. Emacs does no end-of-line conversion and no character code conversion for a binary file. Meanwhile, when you create a new file which is marked by its name as a "text file", Emacs uses DOS end-of-line conversion.
buffer-file-coding-system, this variable is
used to determine which coding system to use when writing the contents
of the buffer. It should be nil for text, t for binary.
If it is t, the coding system is no-conversion.
Otherwise, undecided-dos is used.
Normally this variable is set by visiting a file; it is set to
nil if the file was visited without any actual conversion.
nil for text, t for binary, or a function to call to
compute which. If it is a function, then it is called with a single
argument (the file name) and should return t or nil.
Emacs when running on MS-DOS or MS-Windows checks this alist to decide
which coding system to use when reading a file. For a text file,
undecided-dos is used. For a binary file, no-conversion
is used.
If no element in this alist matches a given file name, then
default-buffer-file-type says how to treat the file.
file-name-buffer-file-type-alist says nothing about the type.
If this variable is non-nil, then these files are treated as
binary: the coding system no-conversion is used. Otherwise,
nothing special is done for them--the coding system is deduced solely
from the file contents, in the usual Emacs fashion.
Input methods provide convenient ways of entering non-ASCII characters from the keyboard. Unlike coding systems, which translate non-ASCII characters to and from encodings meant to be read by programs, input methods provide human-friendly commands. (See section `Input Methods' in The GNU Emacs Manual, for information on how users use input methods to enter text.) How to define input methods is not yet documented in this manual, but here we describe how to use them.
Each input method has a name, which is currently a string; in the future, symbols may also be usable as input method names.
nil if no input method is active in the
buffer now.
current-input-method, this variable is
normally global.
default-input-method to input-method.
If input-method is nil, this function deactivates any input
method for the current buffer.
nil, that is returned
by default, if the user enters empty input. However, if
inhibit-null is non-nil, empty input signals an error.
The returned value is a string.
(input-method language-env activate-func title description args...)
Here input-method is the input method name, a string; language-env is another string, the name of the language environment this input method is recommended for. (That serves only for documentation purposes.)
title is a string to display in the mode line while this method is active. description is a string describing this method and what it is good for.
activate-func is a function to call to activate this method. The args, if any, are passed as arguments to activate-func. All told, the arguments to activate-func are input-method and the args.
The fundamental interface to input methods is through the
variable input-method-function. See section Reading One Event.
GNU Emacs provides two ways to search through a buffer for specified text: exact string searches and regular expression searches. After a regular expression search, you can examine the match data to determine which text matched the whole regular expression or various portions of it.
The `skip-chars...' functions also perform a kind of searching. See section Skipping Characters.
These are the primitive functions for searching through the text in a
buffer. They are meant for use in programs, but you may call them
interactively. If you do so, they prompt for the search string;
limit and noerror are set to nil, and repeat
is set to 1.
These search functions convert the search string to multibyte if the buffer is multibyte; they convert the search string to unibyte if the buffer is unibyte. See section Text Representations.
In the following example, point is initially at the beginning of the
line. Then (search-forward "fox") moves point after the last
letter of `fox':
---------- Buffer: foo ----------
-!-The quick brown fox jumped over the lazy dog.
---------- Buffer: foo ----------
(search-forward "fox")
=> 20
---------- Buffer: foo ----------
The quick brown fox-!- jumped over the lazy dog.
---------- Buffer: foo ----------
The argument limit specifies the upper bound to the search. (It
must be a position in the current buffer.) No match extending after
that position is accepted. If limit is omitted or nil, it
defaults to the end of the accessible portion of the buffer.
What happens when the search fails depends on the value of
noerror. If noerror is nil, a search-failed
error is signaled. If noerror is t, search-forward
returns nil and does nothing. If noerror is neither
nil nor t, then search-forward moves point to the
upper bound and returns nil. (It would be more consistent now to
return the new position of point in that case, but some existing
programs may depend on a value of nil.)
If repeat is supplied (it must be a positive number), then the search is repeated that many times (each time starting at the end of the previous time's match). If these successive searches succeed, the function succeeds, moving point and returning its new value. Otherwise the search fails.
search-forward except that it searches backwards and
leaves point at the beginning of the match.
Word matching regards string as a sequence of words, disregarding punctuation that separates them. It searches the buffer for the same sequence of words. Each word must be distinct in the buffer (searching for the word `ball' does not match the word `balls'), but the details of punctuation and spacing are ignored (searching for `ball boy' does match `ball. Boy!').
In this example, point is initially at the beginning of the buffer; the search leaves it between the `y' and the `!'.
---------- Buffer: foo ----------
-!-He said "Please! Find
the ball boy!"
---------- Buffer: foo ----------
(word-search-forward "Please find the ball, boy.")
=> 35
---------- Buffer: foo ----------
He said "Please! Find
the ball boy-!-!"
---------- Buffer: foo ----------
If limit is non-nil (it must be a position in the current
buffer), then it is the upper bound to the search. The match found must
not extend after that position.
If noerror is nil, then word-search-forward signals
an error if the search fails. If noerror is t, then it
returns nil instead of signaling an error. If noerror is
neither nil nor t, it moves point to limit (or the
end of the buffer) and returns nil.
If repeat is non-nil, then the search is repeated that many
times. Point is positioned at the end of the last match.
word-search-forward
except that it searches backward and normally leaves point at the
beginning of the match.
A regular expression (regexp, for short) is a pattern that denotes a (possibly infinite) set of strings. Searching for matches for a regexp is a very powerful operation. This section explains how to write regexps; the following section says how to search for them.
Regular expressions have a syntax in which a few characters are special constructs and the rest are ordinary. An ordinary character is a simple regular expression that matches that character and nothing else. The special characters are `.', `*', `+', `?', `[', `]', `^', `$', and `\'; no new special characters will be defined in the future. Any other character appearing in a regular expression is ordinary, unless a `\' precedes it.
For example, `f' is not a special character, so it is ordinary, and therefore `f' is a regular expression that matches the string `f' and no other string. (It does not match the string `ff'.) Likewise, `o' is a regular expression that matches only `o'.
Any two regular expressions a and b can be concatenated. The result is a regular expression that matches a string if a matches some amount of the beginning of that string and b matches the rest of the string.
As a simple example, we can concatenate the regular expressions `f' and `o' to get the regular expression `fo', which matches only the string `fo'. Still trivial. To do something more powerful, you need to use one of the special characters. Here is a list of them:
grep.
"\\\\".Please note: For historical compatibility, special characters are treated as ordinary ones if they are in contexts where their special meanings make no sense. For example, `*foo' treats `*' as ordinary since there is no preceding expression on which the `*' can act. It is poor practice to depend on this behavior; quote the special character anyway, regardless of where it appears.
For the most part, `\' followed by any character matches only that character. However, there are several exceptions: two-character sequences starting with `\' which have special meanings. (The second character in such a sequence is always ordinary when used on its own.) Here is a table of `\' constructs.
The following regular expression constructs match the empty string--that is, they don't use up any characters--but whether they match depends on the context.
Not every string is a valid regular expression. For example, a string
with unbalanced square brackets is invalid (with a few exceptions, such
as `[]]'), and so is a string that ends with a single `\'. If
an invalid regular expression is passed to any of the search functions,
an invalid-regexp error is signaled.
(regexp-quote "^The cat$")
=> "\\^The cat\\$"
One use of regexp-quote is to combine an exact string match with
context described as a regular expression. For example, this searches
for the string that is the value of string, surrounded by
whitespace:
(re-search-forward (concat "\\s-" (regexp-quote string) "\\s-"))
If the optional argument paren is non-nil, then the
returned regular expression is always enclosed by at least one
parentheses-grouping construct.
This simplified definition of regexp-opt produces a
regular expression which is equivalent to the actual value
(but not as efficient):
(defun regexp-opt (strings paren)
(let ((open-paren (if paren "\\(" ""))
(close-paren (if paren "\\)" "")))
(concat open-paren
(mapconcat 'regexp-quote strings "\\|")
close-paren)))
Here is a complicated regexp, used by Emacs to recognize the end of a
sentence together with any whitespace that follows. It is the value of
the variable sentence-end.
First, we show the regexp as a string in Lisp syntax to distinguish spaces from tab characters. The string constant begins and ends with a double-quote. `\"' stands for a double-quote as part of the string, `\\' for a backslash as part of the string, `\t' for a tab and `\n' for a newline.
"[.?!][]\"')}]*\\($\\| $\\|\t\\| \\)[ \t\n]*"
In contrast, if you evaluate the variable sentence-end, you
will see the following:
sentence-end
=> "[.?!][]\"')}]*\\($\\| $\\| \\| \\)[
]*"
In this output, tab and newline appear as themselves.
This regular expression contains four parts in succession and can be deciphered as follows:
[.?!]
[]\"')}]*
\" is Lisp syntax for a double-quote in
a string. The `*' at the end indicates that the immediately
preceding regular expression (a character alternative, in this case) may be
repeated zero or more times.
\\($\\| $\\|\t\\| \\)
[ \t\n]*
In GNU Emacs, you can search for the next match for a regular
expression either incrementally or not. For incremental search
commands, see section `Regular Expression Search' in The GNU Emacs Manual. Here we describe only the search functions
useful in programs. The principal one is re-search-forward.
These search functions convert the regular expression to multibyte if the buffer is multibyte; they convert the regular expression to unibyte if the buffer is unibyte. See section Text Representations.
If limit is non-nil (it must be a position in the current
buffer), then it is the upper bound to the search. No match extending
after that position is accepted.
If repeat is supplied (it must be a positive number), then the search is repeated that many times (each time starting at the end of the previous time's match). If all these successive searches succeed, the function succeeds, moving point and returning its new value. Otherwise the function fails.
What happens when the function fails depends on the value of
noerror. If noerror is nil, a search-failed
error is signaled. If noerror is t,
re-search-forward does nothing and returns nil. If
noerror is neither nil nor t, then
re-search-forward moves point to limit (or the end of the
buffer) and returns nil.
In the following example, point is initially before the `T'. Evaluating the search call moves point to the end of that line (between the `t' of `hat' and the newline).
---------- Buffer: foo ----------
I read "-!-The cat in the hat
comes back" twice.
---------- Buffer: foo ----------
(re-search-forward "[a-z]+" nil t 5)
=> 27
---------- Buffer: foo ----------
I read "The cat in the hat-!-
comes back" twice.
---------- Buffer: foo ----------
This function is analogous to re-search-forward, but they are not
simple mirror images. re-search-forward finds the match whose
beginning is as close as possible to the starting point. If
re-search-backward were a perfect mirror image, it would find the
match whose end is as close as possible. However, in fact it finds the
match whose beginning is as close as possible. The reason is that
matching a regular expression at a given spot always works from
beginning to end, and starts at a specified beginning position.
A true mirror-image of re-search-forward would require a special
feature for matching regular expressions from end to beginning. It's
not worth the trouble of implementing that.
nil if
there is no match. If start is non-nil, the search starts
at that index in string.
For example,
(string-match
"quick" "The quick brown fox jumped quickly.")
=> 4
(string-match
"quick" "The quick brown fox jumped quickly." 8)
=> 27
The index of the first character of the string is 0, the index of the second character is 1, and so on.
After this function returns, the index of the first character beyond
the match is available as (match-end 0). See section The Match Data.
(string-match
"quick" "The quick brown fox jumped quickly." 8)
=> 27
(match-end 0)
=> 32
t if so, nil otherwise.
This function does not move point, but it updates the match data, which
you can access using match-beginning and match-end.
See section The Match Data.
In this example, point is located directly before the `T'. If it
were anywhere else, the result would be nil.
---------- Buffer: foo ----------
I read "-!-The cat in the hat
comes back" twice.
---------- Buffer: foo ----------
(looking-at "The cat in the hat$")
=> t
The usual regular expression functions do backtracking when necessary to handle the `\|' and repetition constructs, but they continue this only until they find some match. Then they succeed and report the first match found.
This section describes alternative search functions which perform the full backtracking specified by the POSIX standard for regular expression matching. They continue backtracking until they have tried all possibilities and found all matches, so they can report the longest match, as required by POSIX. This is much slower, so use these functions only when you really need the longest match.
re-search-forward except that it performs the full
backtracking specified by the POSIX standard for regular expression
matching.
re-search-backward except that it performs the full
backtracking specified by the POSIX standard for regular expression
matching.
looking-at except that it performs the full
backtracking specified by the POSIX standard for regular expression
matching.
string-match except that it performs the full
backtracking specified by the POSIX standard for regular expression
matching.
query-replace and related commands.
It searches for occurrences of from-string and replaces some or
all of them. If query-flag is nil, it replaces all
occurrences; otherwise, it asks the user what to do about each one.
If regexp-flag is non-nil, then from-string is
considered a regular expression; otherwise, it must match literally. If
delimited-flag is non-nil, then only replacements
surrounded by word boundaries are considered.
The argument replacements specifies what to replace occurrences with. If it is a string, that string is used. It can also be a list of strings, to be used in cyclic order.
If repeat-count is non-nil, it should be an integer. Then
it specifies how many times to use each of the strings in the
replacements list before advancing cyclicly to the next one.
Normally, the keymap query-replace-map defines the possible user
responses for queries. The argument map, if non-nil, is a
keymap to use instead of query-replace-map.
query-replace and related functions, as well as
y-or-n-p and map-y-or-n-p. It is unusual in two ways:
read-key-sequence to get the input; instead, they read a single
event and look it up "by hand."
Here are the meaningful "bindings" for query-replace-map.
Several of them are meaningful only for query-replace and
friends.
act
skip
exit
act-and-exit
act-and-show
automatic
backup
edit
delete-and-edit
recenter
quit
y-or-n-p and related functions
use this answer.
help
Emacs keeps track of the positions of the start and end of segments of text found during a regular expression search. This means, for example, that you can search for a complex pattern, such as a date in an Rmail message, and then extract parts of the match under control of the pattern.
Because the match data normally describe the most recent search only, you must be careful not to do another search inadvertently between the search you wish to refer back to and the use of the match data. If you can't avoid another intervening search, you must save and restore the match data around it, to prevent it from being overwritten.
This function replaces the text matched by the last search with replacement.
If you did the last search in a buffer, you should specify nil
for string. Then replace-match does the replacement by
editing the buffer; it leaves point at the end of the replacement text,
and returns t.
If you did the search in a string, pass the same string as string.
Then replace-match does the replacement by constructing and
returning a new string.
If fixedcase is non-nil, then the case of the replacement
text is not changed; otherwise, the replacement text is converted to a
different case depending upon the capitalization of the text to be
replaced. If the original text is all upper case, the replacement text
is converted to upper case. If the first word of the original text is
capitalized, then the first word of the replacement text is capitalized.
If the original text contains just one word, and that word is a capital
letter, replace-match considers this a capitalized first word
rather than all upper case.
If case-replace is nil, then case conversion is not done,
regardless of the value of fixed-case. See section Searching and Case.
If literal is non-nil, then replacement is inserted
exactly as it is, the only alterations being case changes as needed.
If it is nil (the default), then the character `\' is treated
specially. If a `\' appears in replacement, then it must be
part of one of the following sequences:
If subexp is non-nil, that says to replace just
subexpression number subexp of the regexp that was matched, not
the entire match. For example, after matching `foo \(ba*r\)',
calling replace-match with 1 as subexp means to replace
just the text that matched `\(ba*r\)'.
This section explains how to use the match data to find out what was matched by the last search or match operation.
You can ask about the entire matching text, or about a particular parenthetical subexpression of a regular expression. The count argument in the functions below specifies which. If count is zero, you are asking about the entire match. If count is positive, it specifies which subexpression you want.
Recall that the subexpressions of a regular expression are those expressions grouped with escaped parentheses, `\(...\)'. The countth subexpression is found by counting occurrences of `\(' from the beginning of the whole regular expression. The first subexpression is numbered 1, the second 2, and so on. Only regular expressions can have subexpressions--after a simple string search, the only information available is about the entire match.
A search which fails may or may not alter the match data. In the past, a failing search did not do this, but we may change it in the future.
nil.
If the last such operation was done against a string with
string-match, then you should pass the same string as the
argument in-string. After a buffer search or match,
you should omit in-string or pass nil for it; but you
should make sure that the current buffer when you call
match-string is the one in which you did the searching or
matching.
match-string except that the result
has no text properties.
If count is zero, then the value is the position of the start of the entire match. Otherwise, count specifies a subexpression in the regular expression, and the value of the function is the starting position of the match for that subexpression.
The value is nil for a subexpression inside a `\|'
alternative that wasn't used in the match.
match-beginning except that it returns the
position of the end of the match, rather than the position of the
beginning.
Here is an example of using the match data, with a comment showing the positions within the text:
(string-match "\\(qu\\)\\(ick\\)"
"The quick fox jumped quickly.")
;0123456789
=> 4
(match-string 0 "The quick fox jumped quickly.")
=> "quick"
(match-string 1 "The quick fox jumped quickly.")
=> "qu"
(match-string 2 "The quick fox jumped quickly.")
=> "ick"
(match-beginning 1) ; The beginning of the match
=> 4 ; with `qu' is at index 4.
(match-beginning 2) ; The beginning of the match
=> 6 ; with `ick' is at index 6.
(match-end 1) ; The end of the match
=> 6 ; with `qu' is at index 6.
(match-end 2) ; The end of the match
=> 9 ; with `ick' is at index 9.
Here is another example. Point is initially located at the beginning of the line. Searching moves point to between the space and the word `in'. The beginning of the entire match is at the 9th character of the buffer (`T'), and the beginning of the match for the first subexpression is at the 13th character (`c').
(list
(re-search-forward "The \\(cat \\)")
(match-beginning 0)
(match-beginning 1))
=> (9 9 13)
---------- Buffer: foo ----------
I read "The cat -!-in the hat comes back" twice.
^ ^
9 13
---------- Buffer: foo ----------
(In this case, the index returned is a buffer position; the first character of the buffer counts as 1.)
The functions match-data and set-match-data read or
write the entire match data, all at once.
(match-beginning n); and
element
corresponds to (match-end n).
All the elements are markers or nil if matching was done on a
buffer, and all are integers or nil if matching was done on a
string with string-match.
As always, there must be no possibility of intervening searches between
the call to a search function and the call to match-data that is
intended to access the match data for that search.
(match-data)
=> (#<marker at 9 in foo>
#<marker at 17 in foo>
#<marker at 13 in foo>
#<marker at 17 in foo>)
match-data.
If match-list refers to a buffer that doesn't exist, you don't get an error; that sets the match data in a meaningless but harmless way.
store-match-data is a semi-obsolete alias for set-match-data.
When you call a function that may do a search, you may need to save and restore the match data around that call, if you want to preserve the match data from an earlier search for later use. Here is an example that shows the problem that arises if you fail to save the match data:
(re-search-forward "The \\(cat \\)")
=> 48
(foo) ; Perhaps foo does
; more searching.
(match-end 0)
=> 61 ; Unexpected result---not 48!
You can save and restore the match data with save-match-data:
You could use set-match-data together with match-data to
imitate the effect of the special form save-match-data. Here is
how:
(let ((data (match-data)))
(unwind-protect
... ; Ok to change the original match data.
(set-match-data data)))
Emacs automatically saves and restores the match data when it runs process filter functions (see section Process Filter Functions) and process sentinels (see section Sentinels: Detecting Process Status Changes).
By default, searches in Emacs ignore the case of the text they are searching through; if you specify searching for `FOO', then `Foo' or `foo' is also considered a match. This applies to regular expressions, too; thus, `[aB]' would match `a' or `A' or `b' or `B'.
If you do not want this feature, set the variable
case-fold-search to nil. Then all letters must match
exactly, including case. This is a buffer-local variable; altering the
variable affects only the current buffer. (See section Introduction to Buffer-Local Variables.) Alternatively, you may change the value of
default-case-fold-search, which is the default value of
case-fold-search for buffers that do not override it.
Note that the user-level incremental search feature handles case distinctions differently. When given a lower case letter, it looks for a match of either case, but when given an upper case letter, it looks for an upper case letter only. But this has nothing to do with the searching functions used in Lisp code.
nil, that means to use the
replacement text verbatim. A non-nil value means to convert the
case of the replacement text according to the text being replaced.
The function replace-match is where this variable actually has
its effect. See section Replacing the Text That Matched.
nil they do not ignore case; otherwise
they do ignore case.
case-fold-search in buffers that do not override it. This is the
same as (default-value 'case-fold-search).
This section describes some variables that hold regular expressions used for certain purposes in editing:
"^\014" (i.e., "^^L" or
"^\C-l"); this matches a line that starts with a formfeed
character.
The following two regular expressions should not assume the match always starts at the beginning of a line; they should not use `^' to anchor the match. Most often, the paragraph commands do check for a match only at the beginning of a line, which means that `^' would be superfluous. When there is a nonzero left margin, they accept matches that start after the left margin. In that case, a `^' would be incorrect. However, a `^' is harmless in modes where a left margin is never used.
paragraph-start also.) The default value is
"[ \t\f]*$", which matches a line that consists entirely of
spaces, tabs, and form feeds (after its left margin).
"[ \t\n\f]", which matches a line starting with a space, tab,
newline, or form feed (after its left margin).
"[.?!][]\"')}]*\\($\\| $\\|\t\\| \\)[ \t\n]*"
This means a period, question mark or exclamation mark, followed optionally by a closing parenthetical character, followed by tabs, spaces or new lines.
For a detailed explanation of this regular expression, see section Complex Regexp Example.
A syntax table specifies the syntactic textual function of each character. This information is used by the parsing functions, the complex movement commands, and others to determine where words, symbols, and other syntactic constructs begin and end. The current syntax table controls the meaning of the word motion functions (see section Motion by Words) and the list motion functions (see section Moving over Balanced Expressions), as well as the functions in this chapter.
A syntax table is a char-table (see section Char-Tables). The element at index c describes the character with code c. The element's value should be a list that encodes the syntax of the character in question.
Syntax tables are used only for moving across text, not for the Emacs Lisp reader. Emacs Lisp uses built-in syntactic rules when reading Lisp expressions, and these rules cannot be changed. (Some Lisp systems provide ways to redefine the read syntax, but we decided to leave this feature out of Emacs Lisp for simplicity.)
Each buffer has its own major mode, and each major mode has its own idea of the syntactic class of various characters. For example, in Lisp mode, the character `;' begins a comment, but in C mode, it terminates a statement. To support these variations, Emacs makes the choice of syntax table local to each buffer. Typically, each major mode has its own syntax table and installs that table in each buffer that uses that mode. Changing this table alters the syntax in all those buffers as well as in any buffers subsequently put in that mode. Occasionally several similar modes share one syntax table. See section Major Mode Examples, for an example of how to set up a syntax table.
A syntax table can inherit the data for some characters from the standard syntax table, while specifying other characters itself. The "inherit" syntax class means "inherit this character's syntax from the standard syntax table." Just changing the standard syntax for a characters affects all syntax tables which inherit from it.
t if object is a syntax table.
This section describes the syntax classes and flags that denote the
syntax of a character, and how they are represented as a syntax
descriptor, which is a Lisp string that you pass to
modify-syntax-entry to specify the syntax you want.
The syntax table specifies a syntax class for each character. There is no necessary relationship between the class of a character in one syntax table and its class in any other table.
Each class is designated by a mnemonic character, which serves as the name of the class when you need to specify a class. Usually the designator character is one that is frequently in that class; however, its meaning as a designator is unvarying and independent of what syntax that character currently has.
A syntax descriptor is a Lisp string that specifies a syntax class, a matching character (used only for the parenthesis classes) and flags. The first character is the designator for a syntax class. The second character is the character to match; if it is unused, put a space there. Then come the characters for any desired flags. If no matching character or flags are needed, one character is sufficient.
For example, the syntax descriptor for the character `*' in C mode is `. 23' (i.e., punctuation, matching character slot unused, second character of a comment-starter, first character of an comment-ender), and the entry for `/' is `. 14' (i.e., punctuation, matching character slot unused, first character of a comment-starter, second character of a comment-ender).
Here is a table of syntax classes, the characters that stand for them, their meanings, and examples of their use.
The class of open parentheses is designated by `(', and that of close parentheses by `)'.
In English text, and in C code, the parenthesis pairs are `()', `[]', and `{}'. In Emacs Lisp, the delimiters for lists and vectors (`()' and `[]') are classified as parenthesis characters.
The parsing facilities of Emacs consider a string as a single token. The usual syntactic meanings of the characters in the string are suppressed.
The Lisp modes have two string quote characters: double-quote (`"') and vertical bar (`|'). `|' is not used in Emacs Lisp, but it is used in Common Lisp. C also has two string quote characters: double-quote for strings, and single-quote (`'') for character constants.
English text has no string quote characters because English is not a programming language. Although quotation marks are used in English, we do not want them to turn off the usual syntactic properties of other characters in the quotation.
Characters in this class count as part of words if
words-include-escapes is non-nil. See section Motion by Words.
Characters in this class count as part of words if
words-include-escapes is non-nil. See section Motion by Words.
This class is used for backslash in TeX mode.
English text has no comment characters. In Lisp, the semicolon (`;') starts a comment and a newline or formfeed ends one.
This syntax class is primarily meant for use with the
syntax-table text property (see section Syntax Properties). You can
mark any range of characters as forming a comment, by giving the first
and last characters of the range syntax-table properties
identifying them as generic comment delimiters.
This syntax class is primarily meant for use with the
syntax-table text property (see section Syntax Properties). You can
mark any range of characters as forming a string constant, by giving the
first and last characters of the range syntax-table properties
identifying them as generic string delimiters.
In addition to the classes, entries for characters in a syntax table can specify flags. There are six possible flags, represented by the characters `1', `2', `3', `4', `b' and `p'.
All the flags except `p' are used to describe multi-character comment delimiters. The digit flags indicate that a character can also be part of a comment sequence, in addition to the syntactic properties associated with its character class. The flags are independent of the class and each other for the sake of characters such as `*' in C mode, which is a punctuation character, and the second character of a start-of-comment sequence (`/*'), and the first character of an end-of-comment sequence (`*/').
Here is a table of the possible flags for a character c, and what they mean:
backward-prefix-chars moves back over these
characters, as well as over characters whose primary syntax class is
prefix (`''). See section Motion and Syntax.
In this section we describe functions for creating, accessing and altering syntax tables.
Most major mode syntax tables are created in this way.
nil), it returns a copy of the
current syntax table. Otherwise, an error is signaled if table is
not a syntax table.
This function always returns nil. The old syntax information in
the table for this character is discarded.
An error is signaled if the first character of the syntax descriptor is not one of the twelve syntax class designator characters. An error is also signaled if char is not a character.
Examples:
;; Put the space character in class whitespace.
(modify-syntax-entry ?\ " ")
=> nil
;; Make `$' an open parenthesis character,
;; with `^' as its matching close.
(modify-syntax-entry ?$ "(^")
=> nil
;; Make `^' a close parenthesis character,
;; with `$' as its matching open.
(modify-syntax-entry ?^ ")$")
=> nil
;; Make `/' a punctuation character,
;; the first character of a start-comment sequence,
;; and the second character of an end-comment sequence.
;; This is used in C mode.
(modify-syntax-entry ?/ ". 14")
=> nil
An error is signaled if char is not a character.
The following examples apply to C mode. The first example shows that the syntax class of space is whitespace (represented by a space). The second example shows that the syntax of `/' is punctuation. This does not show the fact that it is also part of comment-start and -end sequences. The third example shows that open parenthesis is in the class of open parentheses. This does not show the fact that it has a matching character, `)'.
(string (char-syntax ?\ ))
=> " "
(string (char-syntax ?/))
=> "."
(string (char-syntax ?\())
=> "("
We use string to make it easier to see the character returned by
char-syntax.
When the syntax table is not flexible enough to specify the syntax of a
language, you can use syntax-table text properties to override
the syntax table for specific character occurrences in the buffer.
See section Text Properties.
The valid values of syntax-table text property are:
(syntax-code . matching-char)
nil
nil, the character's syntax is determined from
the current syntax table in the usual way.
nil, the syntax scanning functions pay attention
to syntax text properties. Otherwise they use only the current syntax
table.
This section describes functions for moving across characters that have certain syntax classes.
The return value indicates the distance traveled. It is an integer that is zero or less.
Here are several functions for parsing and scanning balanced expressions, also known as sexps, in which parentheses match in pairs. The syntax table controls the interpretation of characters, so these functions can be used for Lisp expressions when in Lisp mode and for C expressions when in C mode. See section Moving over Balanced Expressions, for convenient higher-level functions for moving over balanced expressions.
If state is nil, start is assumed to be at the top
level of parenthesis structure, such as the beginning of a function
definition. Alternatively, you might wish to resume parsing in the
middle of the structure. To do this, you must provide a state
argument that describes the initial status of parsing.
If the third argument target-depth is non-nil, parsing
stops if the depth in parentheses becomes equal to target-depth.
The depth starts at 0, or at whatever is given in state.
If the fourth argument stop-before is non-nil, parsing
stops when it comes to any character that starts a sexp. If
stop-comment is non-nil, parsing stops when it comes to the
start of a comment. If stop-comment is the symbol
syntax-table, parsing stops after the start of a comment or a
string, or the end of a comment or a string, whichever comes first.
The fifth argument state is a nine-element list of the same form
as the value of this function, described below. (It is OK to omit the
last element of the nine.) The return value of one call may be used to
initialize the state of the parse on another call to
parse-partial-sexp.
The result is a list of nine elements describing the final state of the parse:
nil if none.
nil if none.
nil if inside a string. More precisely, this is the
character that will terminate the string, or t if a generic
string delimiter character should terminate it.
t if inside a comment (of either style).
t if point is just after a quote character.
nil for a comment of style "a",
t for a comment of style "b", and syntax-table for
a comment that should be ended by a generic comment delimiter character.
nil.
Elements 0, 3, 4, 5 and 7 are significant in the argument state.
This function is most often used to compute indentation for languages that have nested parentheses.
If depth is nonzero, parenthesis depth counting begins from that
value. The only candidates for stopping are places where the depth in
parentheses becomes zero; scan-lists counts count such
places and then stops. Thus, a positive value for depth means go
out depth levels of parenthesis.
Scanning ignores comments if parse-sexp-ignore-comments is
non-nil.
If the scan reaches the beginning or end of the buffer (or its
accessible portion), and the depth is not zero, an error is signaled.
If the depth is zero but the count is not used up, nil is
returned.
Scanning ignores comments if parse-sexp-ignore-comments is
non-nil.
If the scan reaches the beginning or end of (the accessible part of) the
buffer while in the middle of a parenthetical grouping, an error is
signaled. If it reaches the beginning or end between groupings but
before count is used up, nil is returned.
nil, then comments are treated as
whitespace by the functions in this section and by forward-sexp.
In older Emacs versions, this feature worked only when the comment
terminator is something like `*/', and appears only to end a
comment. In languages where newlines terminate comments, it was
necessary make this variable nil, since not every newline is the
end of a comment. This limitation no longer exists.
You can use forward-comment to move forward or backward over
one comment or several comments.
To move forward over all comments and whitespace following point, use
(forward-comment (buffer-size)). (buffer-size) is a good
argument to use, because the number of comments in the buffer cannot
exceed that many.
Most of the major modes in Emacs have their own syntax tables. Here are several of them:
read
function.)
Lisp programs don't usually work with the elements directly; the Lisp-level syntax table functions usually work with syntax descriptors (see section Syntax Descriptors). Nonetheless, here we document the internal format.
Each element of a syntax table is a cons cell of the form
(syntax-code . matching-char). The CAR,
syntax-code, is an integer that encodes the syntax class, and any
flags. The CDR, matching-char, is non-nil if
a character to match was specified.
This table gives the value of syntax-code which corresponds to each syntactic type.
| Integer Class | Integer Class | Integer Class | |
| 0 whitespace | 5 close parenthesis | 10 character quote | |
| 1 punctuation | 6 expression prefix | 11 comment-start | |
| 2 word | 7 string quote | 12 comment-end | |
| 3 symbol | 8 paired delimiter | 13 inherit | |
| 4 open parenthesis | 9 escape | 14 comment-fence | |
| 15 string-fence |
For example, the usual syntax value for `(' is (4 . 41).
(41 is the character code for `)'.)
The flags are encoded in higher order bits, starting 16 bits from the least significant bit. This table gives the power of two which corresponds to each syntax flag.
| Prefix Flag | Prefix Flag | Prefix Flag | |
| `1' | `3' | `p' | |
| `2' | `4' | `b' |
Categories provide an alternate way of classifying characters syntactically. You can define several categories as needed, then independently assign each character to one or more categories. Unlike syntax classes, categories are not mutually exclusive; it is normal for one character to belong to several categories.
Each buffer has a category table which records which categories are defined and also which characters belong to each category. Each category table defines its own categories, but normally these are initialized by copying from the standard categories table, so that the standard categories are available in all modes.
Each category has a name, which is an ASCII printing character in
the range ` ' to `~'. You specify the name of a category
when you define it with define-category.
The category table is actually a char-table (see section Char-Tables).
The element of the category table at index c is a category
set---a bool-vector--that indicates which categories character c
belongs to. In this category set, if the element at index cat is
t, that means category cat is a member of the set, and that
character c belongs to category cat.
The new category is defined for category table table, which defaults to the current buffer's category table.
(category-docstring ?a)
=> "ASCII"
(category-docstring ?l)
=> "Latin"
nil.
t if object is a category table,
otherwise nil.
nil), it returns a copy of the
current category table. Otherwise, an error is signaled if table
is not a category table.
t for each of those categories, and nil for all
other categories.
(make-category-set "al")
=> #&128"\0\0\0\0\0\0\0\0\0\0\0\0\2\20\0\0"
char-category-set does not
allocate storage, because it returns the same bool-vector that exists in
the category table.
(char-category-set ?a)
=> #&128"\0\0\0\0\0\0\0\0\0\0\0\0\2\20\0\0"
(category-set-mnemonics (char-category-set ?a))
=> "al"
Normally, it modifies the category set by adding category to it.
But if reset is non-nil, then it deletes category
instead.
An abbreviation or abbrev is a string of characters that may be expanded to a longer string. The user can insert the abbrev string and find it replaced automatically with the expansion of the abbrev. This saves typing.
The set of abbrevs currently in effect is recorded in an abbrev table. Each buffer has a local abbrev table, but normally all buffers in the same major mode share one abbrev table. There is also a global abbrev table. Normally both are used.
An abbrev table is represented as an obarray containing a symbol for each abbreviation. The symbol's name is the abbreviation; its value is the expansion; its function definition is the hook function to do the expansion (see section Defining Abbrevs); its property list cell contains the use count, the number of times the abbreviation has been expanded. Because these symbols are not interned in the usual obarray, they will never appear as the result of reading a Lisp expression; in fact, normally they are never used except by the code that handles abbrevs. Therefore, it is safe to use them in an extremely nonstandard way. See section Creating and Interning Symbols.
For the user-level commands for abbrevs, see section `Abbrev Mode' in The GNU Emacs Manual.
Abbrev mode is a minor mode controlled by the value of the variable
abbrev-mode.
nil value of this variable turns on the automatic expansion
of abbrevs when their abbreviations are inserted into a buffer.
If the value is nil, abbrevs may be defined, but they are not
expanded automatically.
This variable automatically becomes buffer-local when set in any fashion.
abbrev-mode for buffers that do not override it.
This is the same as (default-value 'abbrev-mode).
This section describes how to create and manipulate abbrev tables.
nil.
(abbrevname expansion hook
usecount). The return value is always nil.
define-abbrev-table adds the new abbrev table name to this list.
nil.
If human is non-nil, the description is human-oriented.
Otherwise the description is a Lisp expression--a call to
define-abbrev-table that would define name exactly as it
is currently defined.
These functions define an abbrev in a specified abbrev table.
define-abbrev is the low-level basic function, while
add-abbrev is used by commands that ask for information from the
user.
"global" or "mode-specific"); this is used in prompting
the user. The argument arg is the number of words in the
expansion.
The return value is the symbol that internally represents the new
abbrev, or nil if the user declines to confirm redefining an
existing abbrev.
The argument name should be a string. The argument
expansion is normally the desired expansion (a string), or
nil to undefine the abbrev. If it is anything but a string or
nil, then the abbreviation "expands" solely by running
hook.
The argument hook is a function or nil. If hook is
non-nil, then it is called with no arguments after the abbrev is
replaced with expansion; point is located at the end of
expansion when hook is called.
The use count of the abbrev is initialized to zero.
nil, it means that the user plans to use
global abbrevs only. This tells the commands that define mode-specific
abbrevs to define global ones instead. This variable does not alter the
behavior of the functions in this section; it is examined by their
callers.
A file of saved abbrev definitions is actually a file of Lisp code.
The abbrevs are saved in the form of a Lisp program to define the same
abbrev tables with the same contents. Therefore, you can load the file
with load (see section How Programs Do Loading). However, the
function quietly-read-abbrev-file is provided as a more
convenient interface.
User-level facilities such as save-some-buffers can save
abbrevs in a file automatically, under the control of variables
described here.
write-abbrev-file. If filename is
nil, the file specified in abbrev-file-name is used.
save-abbrevs is set to t so that changes will be saved.
This function does not display any messages. It returns nil.
nil value for save-abbrev means that Emacs should
save abbrevs when files are saved. abbrev-file-name specifies
the file to save the abbrevs in.
nil by defining or altering any
abbrevs. This serves as a flag for various Emacs commands to offer to
save your abbrevs.
nil.
Abbrevs are usually expanded by certain interactive commands,
including self-insert-command. This section describes the
subroutines used in writing such commands, as well as the variables they
use for communication.
nil if that abbrev is not
defined. The optional second argument table is the abbrev table
to look it up in. If table is nil, this function tries
first the current buffer's local abbrev table, and second the global
abbrev table.
abbrev-symbol.
t if it did expansion, nil otherwise.
expand-abbrev will use the text from here to point (where it is
then) as the abbrev to expand, rather than using the previous word as
usual.
nil, an abbrev entered entirely in upper
case is expanded using all upper case. Otherwise, an abbrev entered
entirely in upper case is expanded by capitalizing each word of the
expansion.
expand-abbrev to use as the start
of the next abbrev to be expanded. (nil means use the word
before point instead.) abbrev-start-location is set to
nil each time expand-abbrev is called. This variable is
also set by abbrev-prefix-mark.
abbrev-start-location has been set. Trying to expand an abbrev
in any other buffer clears abbrev-start-location. This variable
is set by abbrev-prefix-mark.
abbrev-symbol of the most recent abbrev expanded. This
information is left by expand-abbrev for the sake of the
unexpand-abbrev command (see section `Expanding Abbrevs' in The GNU Emacs Manual).
expand-abbrev for the sake of the
unexpand-abbrev command.
nil if the abbrev
has already been unexpanded. This contains information left by
expand-abbrev for the sake of the unexpand-abbrev command.
The following sample code shows a simple use of
pre-abbrev-expand-hook. If the user terminates an abbrev with a
punctuation character, the hook function asks for confirmation. Thus,
this hook allows the user to decide whether to expand the abbrev, and
aborts expansion if it is not confirmed.
(add-hook 'pre-abbrev-expand-hook 'query-if-not-space) ;; This is the function invoked bypre-abbrev-expand-hook. ;; If the user terminated the abbrev with a space, the function does ;; nothing (that is, it returns so that the abbrev can expand). If the ;; user entered some other character, this function asks whether ;; expansion should continue. ;; If the user answers the prompt with y, the function returns ;;nil(because of thenotfunction), but that is ;; acceptable; the return value has no effect on expansion. (defun query-if-not-space () (if (/= ?\ (preceding-char)) (if (not (y-or-n-p "Do you want to expand this abbrev? ")) (error "Not expanding this abbrev"))))
Here we list the variables that hold the abbrev tables for the preloaded major modes of Emacs.
In the terminology of operating systems, a process is a space in which a program can execute. Emacs runs in a process. Emacs Lisp programs can invoke other programs in processes of their own. These are called subprocesses or child processes of the Emacs process, which is their parent process.
A subprocess of Emacs may be synchronous or asynchronous, depending on how it is created. When you create a synchronous subprocess, the Lisp program waits for the subprocess to terminate before continuing execution. When you create an asynchronous subprocess, it can run in parallel with the Lisp program. This kind of subprocess is represented within Emacs by a Lisp object which is also called a "process". Lisp programs can use this object to communicate with the subprocess or to control it. For example, you can send signals, obtain status information, receive output from the process, or send input to it.
t if object is a process,
nil otherwise.
There are three functions that create a new subprocess in which to run
a program. One of them, start-process, creates an asynchronous
process and returns a process object (see section Creating an Asynchronous Process).
The other two, call-process and call-process-region,
create a synchronous process and do not return a process object
(see section Creating a Synchronous Process).
Synchronous and asynchronous processes are explained in following sections. Since the three functions are all called in a similar fashion, their common arguments are described here.
In all cases, the function's program argument specifies the
program to be run. An error is signaled if the file is not found or
cannot be executed. If the file name is relative, the variable
exec-path contains a list of directories to search. Emacs
initializes exec-path when it starts up, based on the value of
the environment variable PATH. The standard file name
constructs, `~', `.', and `..', are interpreted as usual
in exec-path, but environment variable substitutions
(`$HOME', etc.) are not recognized; use
substitute-in-file-name to perform them (see section Functions that Expand Filenames).
Each of the subprocess-creating functions has a buffer-or-name
argument which specifies where the standard output from the program will
go. It should be a buffer or a buffer name; if it is a buffer name,
that will create the buffer if it does not already exist. It can also
be nil, which says to discard the output unless a filter function
handles it. (See section Process Filter Functions, and section Reading and Printing Lisp Objects.)
Normally, you should avoid having multiple processes send output to the
same buffer because their output would be intermixed randomly.
All three of the subprocess-creating functions have a &rest
argument, args. The args must all be strings, and they are
supplied to program as separate command line arguments. Wildcard
characters and other shell constructs have no special meanings in these
strings, since the whole strings are passed directly to the specified
program.
Please note: The argument program contains only the name of the program; it may not contain any command-line arguments. You must use args to provide those.
The subprocess gets its current directory from the value of
default-directory (see section Functions that Expand Filenames).
The subprocess inherits its environment from Emacs, but you can
specify overrides for it with process-environment. See section Operating System Environment.
movemail is an example of such a program;
Rmail uses it to fetch new mail from an inbox.
nil, which stands for the default
directory (which is the value of default-directory).
The value of exec-path is used by call-process and
start-process when the program argument is not an absolute
file name.
Lisp programs sometimes need to run a shell and give it a command
which contains file names that were specified by the user. These
programs ought to be able to support any valid file name. But the shell
gives special treatment to certain characters, and if these characters
occur in the file name, they will confuse the shell. To handle these
characters, use the function shell-quote-argument:
Precisely what this function does depends on your operating system. The function is designed to work with the usual shell syntax; if you use an unusual shell, you will need to redefine this function. On MS-DOS, the function returns argument unchanged; while this is not really correct, it is the best one can do, since the MS-DOS shell has no quoting features.
;; This example shows the behavior on GNU and Unix systems.
(shell-quote-argument "foo > bar")
=> "foo\\ \\>\\ bar"
Here's an example of using shell-quote-argument to construct
a shell command:
(concat "diff -c "
(shell-quote-argument oldfile)
" "
(shell-quote-argument newfile))
After a synchronous process is created, Emacs waits for the
process to terminate before continuing. Starting Dired is an example of
this: it runs ls in a synchronous process, then modifies the
output slightly. Because the process is synchronous, the entire
directory listing arrives in the buffer before Emacs tries to do
anything with it.
While Emacs waits for the synchronous subprocess to terminate, the
user can quit by typing C-g. The first C-g tries to kill
the subprocess with a SIGINT signal; but it waits until the
subprocess actually terminates before quitting. If during that time the
user types another C-g, that kills the subprocess instantly with
SIGKILL and quits immediately. See section Quitting.
The synchronous subprocess functions return an indication of how the process terminated.
The output from a synchronous subprocess is generally decoded using a
coding system, much like text read from a file. The input sent to a
subprocess by call-process-region is encoded using a coding
system, much like text written into a file. See section Coding Systems.
The standard input for the process comes from file infile if
infile is not nil, and from `/dev/null' otherwise.
The argument destination says where to put the process output.
Here are the possibilities:
t
nil
(real-destination error-destination)
nil, that means to discard the
error output, t means mix it with the ordinary output, and a
string specifies a file name to redirect error output into.
You can't directly specify a buffer to put the error output in; that is
too difficult to implement. But you can achieve this result by sending
the error output to a temporary file and then inserting the file into a
buffer.
If display is non-nil, then call-process redisplays
the buffer as output is inserted. (However, if the coding system chosen
for decoding output is undecided, meaning deduce the encoding
from the actual data, then redisplay sometimes cannot continue once
non-ASCII characters are encountered. There are fundamental
reasons why it is hard to fix this.) Otherwise the function
call-process does no redisplay, and the results become visible on
the screen only when Emacs redisplays that buffer in the normal course
of events.
The remaining arguments, args, are strings that specify command line arguments for the program.
The value returned by call-process (unless you told it not to
wait) indicates the reason for process termination. A number gives the
exit status of the subprocess; 0 means success, and any other value
means failure. If the process terminated with a signal,
call-process returns a string describing the signal.
In the examples below, the buffer `foo' is current.
(call-process "pwd" nil t)
=> nil
---------- Buffer: foo ----------
/usr/user/lewis/manual
---------- Buffer: foo ----------
(call-process "grep" nil "bar" nil "lewis" "/etc/passwd")
=> nil
---------- Buffer: bar ----------
lewis:5LTsHm66CSWKg:398:21:Bil Lewis:/user/lewis:/bin/csh
---------- Buffer: bar ----------
Here is a good example of the use of call-process, which used to
be found in the definition of insert-directory:
(call-process insert-directory-program nil t nil switches
(if full-directory-p
(concat (file-name-as-directory file) ".")
file))
nil; this is useful when
destination is t, to insert the output in the current
buffer in place of the input.
The arguments destination and display control what to do
with the output from the subprocess, and whether to update the display
as it comes in. For details, see the description of
call-process, above. If destination is the integer 0,
call-process-region discards the output and returns nil
immediately, without waiting for the subprocess to finish.
The remaining arguments, args, are strings that specify command line arguments for the program.
The return value of call-process-region is just like that of
call-process: nil if you told it to return without
waiting; otherwise, a number or string which indicates how the
subprocess terminated.
In the following example, we use call-process-region to run the
cat utility, with standard input being the first five characters
in buffer `foo' (the word `input'). cat copies its
standard input into its standard output. Since the argument
destination is t, this output is inserted in the current
buffer.
---------- Buffer: foo ----------
input-!-
---------- Buffer: foo ----------
(call-process-region 1 6 "cat" nil t)
=> nil
---------- Buffer: foo ----------
inputinput-!-
---------- Buffer: foo ----------
The shell-command-on-region command uses
call-process-region like this:
(call-process-region
start end
shell-file-name ; Name of program.
nil ; Do not delete region.
buffer ; Send output to buffer.
nil ; No redisplay during output.
"-c" command) ; Arguments for the shell.
After an asynchronous process is created, Emacs and the subprocess both continue running immediately. The process thereafter runs in parallel with Emacs, and the two can communicate with each other using the functions described in following sections. However, communication is only partially asynchronous: Emacs sends data to the process only when certain functions are called, and Emacs accepts data from the process only when Emacs is waiting for input or for a time delay.
Here we describe how to create an asynchronous process.
The remaining arguments, args, are strings that specify command line arguments for the program.
In the example below, the first process is started and runs (rather, sleeps) for 100 seconds. Meanwhile, the second process is started, and given the name `my-process<1>' for the sake of uniqueness. It inserts the directory listing at the end of the buffer `foo', before the first process finishes. Then it finishes, and a message to that effect is inserted in the buffer. Much later, the first process finishes, and another message is inserted in the buffer for it.
(start-process "my-process" "foo" "sleep" "100")
=> #<process my-process>
(start-process "my-process" "foo" "ls" "-l" "/user/lewis/bin")
=> #<process my-process<1>>
---------- Buffer: foo ----------
total 2
lrwxrwxrwx 1 lewis 14 Jul 22 10:12 gnuemacs --> /emacs
-rwxrwxrwx 1 lewis 19 Jul 30 21:02 lemon
Process my-process<1> finished
Process my-process finished
---------- Buffer: foo ----------
start-process except that it uses a shell
to execute the specified command. The argument command is a shell
command name, and command-args are the arguments for the shell
command. The variable shell-file-name specifies which shell to
use.
The point of running a program through the shell, rather than directly
with start-process, is so that you can employ shell features such
as wildcards in the arguments. It follows that if you include an
arbitrary user-specified filename in the command, you should quote it
with shell-quote-argument first, so that any special shell
characters in the file name do not have their special shell
meanings. See section Shell Arguments.
nil, then PTYs are
used, when available. Otherwise, pipes are used.
PTYs are usually preferable for processes visible to the user, as in Shell mode, because they allow job control (C-c, C-z, etc.) to work between the process and its children, whereas pipes do not. For subprocesses used for internal purposes by programs, it is often better to use a pipe, because they are more efficient. In addition, the total number of PTYs is limited on many systems and it is good not to waste them.
The value process-connection-type is used when
start-process is called. So you can specify how to communicate
with one subprocess by binding the variable around the call to
start-process.
(let ((process-connection-type nil)) ; Use a pipe. (start-process ...))
To determine whether a given subprocess actually got a pipe or a
PTY, use the function process-tty-name (see section Process Information).
Deleting a process disconnects Emacs immediately from the subprocess, and removes it from the list of active processes. It sends a signal to the subprocess to make the subprocess terminate, but this is not guaranteed to happen immediately. The process object itself continues to exist as long as other Lisp objects point to it. The process mark continues to point to the same place as before (usually into a buffer where output from the process was being inserted).
You can delete a process explicitly at any time. Processes are deleted automatically after they terminate, but not necessarily right away. If you delete a terminated process explicitly before it is deleted automatically, no harm results.
exit or to a signal). If it is
nil, then they continue to exist until the user runs
list-processes. Otherwise, they are deleted immediately after
they exit.
SIGHUP signal. The argument name may be a process,
the name of a process, a buffer, or the name of a buffer.
(delete-process "*shell*")
=> nil
nil, the process will be deleted silently.
Otherwise, Emacs will query about killing it.
The value is t if the process was formerly set up to require
query, nil otherwise. A newly-created process always requires
query.
(process-kill-without-query (get-process "shell"))
=> t
Several functions return information about processes.
list-processes is provided for interactive use.
nil.
(process-list)
=> (#<process display-time> #<process shell>)
nil if
there is none. An error is signaled if name is not a string.
(get-process "shell")
=> #<process shell>
(process-command (get-process "shell"))
=> ("/bin/csh" "-i")
t for an ordinary child process, and
(hostname service) for a net connection
(see section Network Connections).
The possible values for an actual subprocess are:
run
stop
exit
signal
open
closed
nil
(process-status "shell")
=> run
(process-status (get-buffer "*shell*"))
=> run
x
=> #<process xx<1>>
(process-status x)
=> exit
For a network connection, process-status returns one of the symbols
open or closed. The latter means that the other side
closed the connection, or Emacs did delete-process.
process-status to
determine which of those it is.) If process has not yet
terminated, the value is 0.
nil if it is using pipes
instead of a terminal (see process-connection-type in
section Creating an Asynchronous Process).
(coding-system-for-decoding . coding-system-for-encoding)
Asynchronous subprocesses receive input when it is sent to them by Emacs, which is done with the functions in this section. You must specify the process to send input to, and the input data to send. The data appears on the "standard input" of the subprocess.
Some operating systems have limited space for buffered input in a PTY. On these systems, Emacs sends an EOF periodically amidst the other characters, to force them through. For most programs, these EOFs do no harm.
Subprocess input is normally encoded using a coding system before the
subprocess receives it, much like text written into a file. You can use
set-process-coding-system to specify which coding system to use
(see section Process Information). Otherwise, the coding system comes from
coding-system-for-write, if that is non-nil; or else from
the defaulting mechanism (see section Default Coding Systems).
nil, the current buffer's
process is used.
The function returns nil.
(process-send-string "shell<1>" "ls\n")
=> nil
---------- Buffer: *shell* ----------
...
introduction.texi syntax-tables.texi~
introduction.texi~ text.texi
introduction.txt text.texi~
...
---------- Buffer: *shell* ----------
nil, the current buffer's process is
used.)
An error is signaled unless both start and end are integers or markers that indicate positions in the current buffer. (It is unimportant which number is larger.)
If process-name is not supplied, or if it is nil, then
this function sends the EOF to the current buffer's process. An
error is signaled if the current buffer has no process.
The function returns process-name.
(process-send-eof "shell")
=> "shell"
Sending a signal to a subprocess is a way of interrupting its
activities. There are several different signals, each with its own
meaning. The set of signals and their names is defined by the operating
system. For example, the signal SIGINT means that the user has
typed C-c, or that some analogous thing has happened.
Each signal has a standard effect on the subprocess. Most signals kill the subprocess, but some stop or resume execution instead. Most signals can optionally be handled by programs; if the program handles the signal, then we can say nothing in general about its effects.
You can send signals explicitly by calling the functions in this
section. Emacs also sends signals automatically at certain times:
killing a buffer sends a SIGHUP signal to all its associated
processes; killing Emacs sends a SIGHUP signal to all remaining
processes. (SIGHUP is a signal that usually indicates that the
user hung up the phone.)
Each of the signal-sending functions takes two optional arguments: process-name and current-group.
The argument process-name must be either a process, the name of
one, or nil. If it is nil, the process defaults to the
process associated with the current buffer. An error is signaled if
process-name does not identify a process.
The argument current-group is a flag that makes a difference
when you are running a job-control shell as an Emacs subprocess. If it
is non-nil, then the signal is sent to the current process-group
of the terminal that Emacs uses to communicate with the subprocess. If
the process is a job-control shell, this means the shell's current
subjob. If it is nil, the signal is sent to the process group of
the immediate subprocess of Emacs. If the subprocess is a job-control
shell, this is the shell itself.
The flag current-group has no effect when a pipe is used to
communicate with the subprocess, because the operating system does not
support the distinction in the case of pipes. For the same reason,
job-control shells won't work when a pipe is used. See
process-connection-type in section Creating an Asynchronous Process.
SIGINT. Outside of Emacs, typing the "interrupt
character" (normally C-c on some systems, and DEL on
others) sends this signal. When the argument current-group is
non-nil, you can think of this function as "typing C-c"
on the terminal by which Emacs talks to the subprocess.
SIGKILL. This signal kills the subprocess immediately,
and cannot be handled by the subprocess.
SIGQUIT to the process
process-name. This signal is the one sent by the "quit
character" (usually C-b or C-\) when you are not inside
Emacs.
SIGTSTP. Use continue-process to resume its
execution.
Outside of Emacs, on systems with job control, the "stop character"
(usually C-z) normally sends this signal. When
current-group is non-nil, you can think of this function as
"typing C-z" on the terminal Emacs uses to communicate with the
subprocess.
SIGCONT. This presumes that process-name was
stopped previously.
There are two ways to receive the output that a subprocess writes to its standard output stream. The output can be inserted in a buffer, which is called the associated buffer of the process, or a function called the filter function can be called to act on the output. If the process has no buffer and no filter function, its output is discarded.
Output from a subprocess can arrive only while Emacs is waiting: when
reading terminal input, in sit-for and sleep-for
(see section Waiting for Elapsed Time or Input), and in accept-process-output (see section Accepting Output from Processes). This minimizes the problem of timing errors that usually
plague parallel programming. For example, you can safely create a
process and only then specify its buffer or filter function; no output
can arrive before you finish, if the code in between does not call any
primitive that waits.
Subprocess output is normally decoded using a coding system before the
buffer or filter function receives it, much like text read from a file.
You can use set-process-coding-system to specify which coding
system to use (see section Process Information). Otherwise, the coding
system comes from coding-system-for-read, if that is
non-nil; or else from the defaulting mechanism (see section Default Coding Systems).
Warning: Coding systems such as undecided which
determine the coding system from the data do not work entirely reliably
with asynchronous subprocess output. This is because Emacs has to
process asynchronous subprocess output in batches, as it arrives. Emacs
must try to detect the proper coding system from one batch at a time,
and this does not always work. Therefore, if at all possible, use a
coding system which determines both the character code conversion and
the end of line conversion--that is, one like latin-1-unix,
rather than undecided or latin-1.
A process can (and usually does) have an associated buffer, which is an ordinary Emacs buffer that is used for two purposes: storing the output from the process, and deciding when to kill the process. You can also use the buffer to identify a process to operate on, since in normal practice only one process is associated with any given buffer. Many applications of processes also use the buffer for editing input to be sent to the process, but this is not built into Emacs Lisp.
Unless the process has a filter function (see section Process Filter Functions),
its output is inserted in the associated buffer. The position to insert
the output is determined by the process-mark, which is then
updated to point to the end of the text just inserted. Usually, but not
always, the process-mark is at the end of the buffer.
(process-buffer (get-process "shell"))
=> #<buffer *shell*>
If process does not have a buffer, process-mark returns a
marker that points nowhere.
Insertion of process output in a buffer uses this marker to decide where to insert, and updates it to point after the inserted text. That is why successive batches of output are inserted consecutively.
Filter functions normally should use this marker in the same fashion
as is done by direct insertion of output in the buffer. A good
example of a filter function that uses process-mark is found at
the end of the following section.
When the user is expected to enter input in the process buffer for transmission to the process, the process marker separates the new input from previous output.
nil, the process becomes
associated with no buffer.
(get-buffer-process "*shell*")
=> #<process shell>
Killing the process's buffer deletes the process, which kills the
subprocess with a SIGHUP signal (see section Sending Signals to Processes).
A process filter function is a function that receives the standard output from the associated process. If a process has a filter, then all output from that process is passed to the filter. The process buffer is used directly for output from the process only when there is no filter.
The filter function can only be called when Emacs is waiting for
something, because process output arrives only at such times. Emacs
waits when reading terminal input, in sit-for and
sleep-for (see section Waiting for Elapsed Time or Input), and in accept-process-output
(see section Accepting Output from Processes).
A filter function must accept two arguments: the associated process and a string, which is output just received from it. The function is then free to do whatever it chooses with the output.
Quitting is normally inhibited within a filter function--otherwise,
the effect of typing C-g at command level or to quit a user
command would be unpredictable. If you want to permit quitting inside a
filter function, bind inhibit-quit to nil.
See section Quitting.
If an error happens during execution of a filter function, it is
caught automatically, so that it doesn't stop the execution of whatever
program was running when the filter function was started. However, if
debug-on-error is non-nil, the error-catching is turned
off. This makes it possible to use the Lisp debugger to debug the
filter function. See section The Lisp Debugger.
Many filter functions sometimes or always insert the text in the
process's buffer, mimicking the actions of Emacs when there is no
filter. Such filter functions need to use set-buffer in order to
be sure to insert in that buffer. To avoid setting the current buffer
semipermanently, these filter functions must save and restore the
current buffer. They should also update the process marker, and in some
cases update the value of point. Here is how to do these things:
(defun ordinary-insertion-filter (proc string)
(with-current-buffer (process-buffer proc)
(let ((moving (= (point) (process-mark proc))))
(save-excursion
;; Insert the text, advancing the process marker.
(goto-char (process-mark proc))
(insert string)
(set-marker (process-mark proc) (point)))
(if moving (goto-char (process-mark proc))))))
The reason to use with-current-buffer, rather than using
save-excursion to save and restore the current buffer, is so as
to preserve the change in point made by the second call to
goto-char.
To make the filter force the process buffer to be visible whenever new
text arrives, insert the following line just before the
with-current-buffer construct:
(display-buffer (process-buffer proc))
To force point to the end of the new output, no matter where it was
previously, eliminate the variable moving and call
goto-char unconditionally.
In earlier Emacs versions, every filter function that did regular expression searching or matching had to explicitly save and restore the match data. Now Emacs does this automatically for filter functions; they never need to do it explicitly. See section The Match Data.
A filter function that writes the output into the buffer of the
process should check whether the buffer is still alive. If it tries to
insert into a dead buffer, it will get an error. The expression
(buffer-name (process-buffer process)) returns nil
if the buffer is dead.
The output to the function may come in chunks of any size. A program that produces the same output twice in a row may send it as one batch of 200 characters one time, and five batches of 40 characters the next. If the filter looks for certain text strings in the subprocess output, make sure to handle the case where one of these strings is split across two or more batches of output.
nil, it gives the process no filter.
nil
if it has none.
Here is an example of use of a filter function:
(defun keep-output (process output)
(setq kept (cons output kept)))
=> keep-output
(setq kept nil)
=> nil
(set-process-filter (get-process "shell") 'keep-output)
=> keep-output
(process-send-string "shell" "ls ~/other\n")
=> nil
kept
=> ("lewis@slug[8] % "
"FINAL-W87-SHORT.MSS backup.otl kolstad.mss~
address.txt backup.psf kolstad.psf
backup.bib~ david.mss resume-Dec-86.mss~
backup.err david.psf resume-Dec.psf
backup.mss dland syllabus.mss
"
"#backups.mss# backup.mss~ kolstad.mss
")
Output from asynchronous subprocesses normally arrives only while Emacs is waiting for some sort of external event, such as elapsed time or terminal input. Occasionally it is useful in a Lisp program to explicitly permit output to arrive at a specific point, or even to wait until output arrives from a process.
nil then this function does
not return until some output has been received from process.
The arguments seconds and millisec let you specify timeout
periods. The former specifies a period measured in seconds and the
latter specifies one measured in milliseconds. The two time periods
thus specified are added together, and accept-process-output
returns after that much time whether or not there has been any
subprocess output.
The argument seconds need not be an integer. If it is a floating point number, this function waits for a fractional number of seconds. Some systems support only a whole number of seconds; on these systems, seconds is rounded down.
Not all operating systems support waiting periods other than multiples of a second; on those that do not, you get an error if you specify nonzero millisec.
The function accept-process-output returns non-nil if it
did get some output, or nil if the timeout expired before output
arrived.
A process sentinel is a function that is called whenever the associated process changes status for any reason, including signals (whether sent by Emacs or caused by the process's own actions) that terminate, stop, or continue the process. The process sentinel is also called if the process exits. The sentinel receives two arguments: the process for which the event occurred, and a string describing the type of event.
The string describing the event looks like one of the following:
"finished\n".
"exited abnormally with code exitcode\n".
"name-of-signal\n".
"name-of-signal (core dumped)\n".
A sentinel runs only while Emacs is waiting (e.g., for terminal input,
or for time to elapse, or for process output). This avoids the timing
errors that could result from running them at random places in the
middle of other Lisp programs. A program can wait, so that sentinels
will run, by calling sit-for or sleep-for
(see section Waiting for Elapsed Time or Input), or accept-process-output (see section Accepting Output from Processes). Emacs also allows sentinels to run when the command loop is
reading input.
Quitting is normally inhibited within a sentinel--otherwise, the
effect of typing C-g at command level or to quit a user command
would be unpredictable. If you want to permit quitting inside a
sentinel, bind inhibit-quit to nil. See section Quitting.
A sentinel that writes the output into the buffer of the process
should check whether the buffer is still alive. If it tries to insert
into a dead buffer, it will get an error. If the buffer is dead,
(buffer-name (process-buffer process)) returns nil.
If an error happens during execution of a sentinel, it is caught
automatically, so that it doesn't stop the execution of whatever
programs was running when the sentinel was started. However, if
debug-on-error is non-nil, the error-catching is turned
off. This makes it possible to use the Lisp debugger to debug the
sentinel. See section The Lisp Debugger.
In earlier Emacs versions, every sentinel that did regular expression searching or matching had to explicitly save and restore the match data. Now Emacs does this automatically for sentinels; they never need to do it explicitly. See section The Match Data.
nil, then the process will have no sentinel.
The default behavior when there is no sentinel is to insert a message in
the process's buffer when the process status changes.
(defun msg-me (process event)
(princ
(format "Process: %s had the event `%s'" process event)))
(set-process-sentinel (get-process "shell") 'msg-me)
=> msg-me
(kill-process (get-process "shell"))
-| Process: #<process shell> had the event `killed'
=> #<process shell>
nil if it
has none.
nil if Emacs was waiting for keyboard input from the user at
the time the sentinel or filter function was called, nil if it
was not.
You can use a transaction queue to communicate with a subprocess
using transactions. First use tq-create to create a transaction
queue communicating with a specified process. Then you can call
tq-enqueue to send a transaction.
The argument question is the outgoing message that starts the transaction. The argument fn is the function to call when the corresponding answer comes back; it is called with two arguments: closure, and the answer received.
The argument regexp is a regular expression that should match the
entire answer, but nothing less; that's how tq-enqueue determines
where the answer ends.
The return value of tq-enqueue itself is not meaningful.
Transaction queues are implemented by means of a filter function. See section Process Filter Functions.
Emacs Lisp programs can open TCP network connections to other processes on
the same machine or other machines. A network connection is handled by Lisp
much like a subprocess, and is represented by a process object.
However, the process you are communicating with is not a child of the
Emacs process, so you can't kill it or send it signals. All you can do
is send and receive data. delete-process closes the connection,
but does not kill the process at the other end; that process must decide
what to do about closure of the connection.
You can distinguish process objects representing network connections
from those representing subprocesses with the process-status
function. It always returns either open or closed for a
network connection, and it never returns either of those values for a
real subprocess. See section Process Information.
The name argument specifies the name for the process object. It is modified as necessary to make it unique.
The buffer-or-name argument is the buffer to associate with the
connection. Output from the connection is inserted in the buffer,
unless you specify a filter function to handle the output. If
buffer-or-name is nil, it means that the connection is not
associated with any buffer.
The arguments host and service specify where to connect to; host is the host name (a string), and service is the name of a defined network service (a string) or a port number (an integer).
This chapter is about starting and getting out of Emacs, access to values in the operating system environment, and terminal input, output, and flow control.
See section Building Emacs, for related information. See also section Emacs Display, for additional operating system status information pertaining to the terminal and the screen.
This section describes what Emacs does when it is started, and how you can customize these actions.
The order of operations performed (in `startup.el') by Emacs when it is started up is as follows:
load-path, by running the file
named `subdirs.el' in each directory that is listed.
LANG.
before-init-hook.
inhibit-default-init
is non-nil. (This is not done in `-batch' mode or if
`-q' was specified on the command line.) The library's file name
is usually `default.el'.
after-init-hook.
initial-major-mode, provided
the buffer `*scratch*' is still current and still in Fundamental
mode.
inhibit-startup-echo-area-message.
term-setup-hook.
frame-notice-user-settings, which modifies the
parameters of the selected frame according to whatever the init files
specify.
window-setup-hook. See section Window Systems.
inhibit-startup-message is nil, and the
buffer is still empty.
nil, then the messages are not printed.
This variable exists so you can set it in your personal init file, once you are familiar with the contents of the startup message. Do not set this variable in the init file of a new user, or in a way that affects more than one user, because that would prevent new users from receiving the information they are supposed to see.
(setq inhibit-startup-echo-area-message
"your-login-name")
Emacs explicitly checks for an expression as shown above in your
`.emacs' file; your login name must appear in the expression as a
Lisp string constant. Other methods of setting
inhibit-startup-echo-area-message to the same value do not
inhibit the startup message.
This way, you can easily inhibit the message for yourself if you wish, but thoughtless copying of your `.emacs' file will not inhibit the message for someone else.
When you start Emacs, it normally attempts to load the file `.emacs' from your home directory. This file, if it exists, must contain Lisp code. It is called your init file. The command line switches `-q' and `-u' affect the use of the init file; `-q' says not to load an init file, and `-u' says to load a specified user's init file instead of yours. See section `Entering Emacs' in The GNU Emacs Manual.
A site may have a default init file, which is the library named
`default.el'. Emacs finds the `default.el' file through the
standard search path for libraries (see section How Programs Do Loading).
The Emacs distribution does not come with this file; sites may provide
one for local customizations. If the default init file exists, it is
loaded whenever you start Emacs, except in batch mode or if `-q' is
specified. But your own personal init file, if any, is loaded first; if
it sets inhibit-default-init to a non-nil value, then
Emacs does not subsequently load the `default.el' file.
Another file for site-customization is `site-start.el'. Emacs loads this before the user's init file. You can inhibit the loading of this file with the option `-no-site-file'.
"site-start". The only
way you can change it with real effect is to do so before dumping
Emacs.
If there is a great deal of code in your `.emacs' file, you
should move it into another file named `something.el',
byte-compile it (see section Byte Compilation), and make your `.emacs'
file load the other file using load (see section Loading).
See section `Init File Examples' in The GNU Emacs Manual, for examples of how to make various commonly desired customizations in your `.emacs' file.
nil,
then the default library is not loaded. The default value is
nil.
Each terminal type can have its own Lisp library that Emacs loads when
run on that type of terminal. The library's name is constructed by
concatenating the value of the variable term-file-prefix and the
terminal type. Normally, term-file-prefix has the value
"term/"; changing this is not recommended. Emacs finds the file
in the normal manner, by searching the load-path directories, and
trying the `.elc' and `.el' suffixes.
The usual function of a terminal-specific library is to enable special
keys to send sequences that Emacs can recognize. It may also need to
set or add to function-key-map if the Termcap entry does not
specify all the terminal's function keys. See section Terminal Input.
When the name of the terminal type contains a hyphen, only the part of
the name before the first hyphen is significant in choosing the library
name. Thus, terminal types `aaa-48' and `aaa-30-rv' both use
the `term/aaa' library. If necessary, the library can evaluate
(getenv "TERM") to find the full name of the terminal
type.
Your `.emacs' file can prevent the loading of the
terminal-specific library by setting the variable
term-file-prefix to nil. This feature is useful when
experimenting with your own peculiar customizations.
You can also arrange to override some of the actions of the
terminal-specific library by setting the variable
term-setup-hook. This is a normal hook which Emacs runs using
run-hooks at the end of Emacs initialization, after loading both
your `.emacs' file and any terminal-specific libraries. You can
use this variable to define initializations for terminals that do not
have their own libraries. See section Hooks.
term-file-prefix variable is non-nil, Emacs loads
a terminal-specific initialization file as follows:
(load (concat term-file-prefix (getenv "TERM")))
You may set the term-file-prefix variable to nil in your
`.emacs' file if you do not wish to load the
terminal-initialization file. To do this, put the following in
your `.emacs' file: (setq term-file-prefix nil).
You can use term-setup-hook to override the definitions made by a
terminal-specific file.
See window-setup-hook in section Window Systems, for a related
feature.
You can use command line arguments to request various actions when you start Emacs. Since you do not need to start Emacs more than once per day, and will often leave your Emacs session running longer than that, command line arguments are hardly ever used. As a practical matter, it is best to avoid making the habit of using them, since this habit would encourage you to kill and restart Emacs unnecessarily often. These options exist for two reasons: to be compatible with other editors (for invocation by other programs) and to enable shell scripts to run specific Lisp programs.
This section describes how Emacs processes command line arguments, and how you can customize them.
t once the command line has been
processed.
If you redump Emacs by calling dump-emacs, you may wish to set
this variable to nil first in order to cause the new dumped Emacs
to process its new command line arguments.
A command line option is an argument on the command line of the form:
-option
The elements of the command-switch-alist look like this:
(option . handler-function)
The handler-function is called to handle option and receives the option name as its sole argument.
In some cases, the option is followed in the command line by an
argument. In these cases, the handler-function can find all the
remaining command-line arguments in the variable
command-line-args-left. (The entire list of command-line
arguments is in command-line-args.)
The command line arguments are parsed by the command-line-1
function in the `startup.el' file. See also section `Command Line Switches and Arguments' in The GNU Emacs Manual.
nil
value.
These functions are called with no arguments. They can access the
command-line argument under consideration through the variable
argi, which is bound temporarily at this point. The remaining
arguments (not including the current one) are in the variable
command-line-args-left.
When a function recognizes and processes the argument in argi, it
should return a non-nil value to say it has dealt with that
argument. If it has also dealt with some of the following arguments, it
can indicate that by deleting them from command-line-args-left.
If all of these functions return nil, then the argument is used
as a file name to visit.
There are two ways to get out of Emacs: you can kill the Emacs job, which exits permanently, or you can suspend it, which permits you to reenter the Emacs process later. As a practical matter, you seldom kill Emacs--only when you are about to log out. Suspending is much more common.
Killing Emacs means ending the execution of the Emacs process. The
parent process normally resumes control. The low-level primitive for
killing Emacs is kill-emacs.
If exit-data is an integer, then it is used as the exit status of the Emacs process. (This is useful primarily in batch operation; see section Batch Mode.)
If exit-data is a string, its contents are stuffed into the terminal input buffer so that the shell (or whatever program next reads input) can read them.
All the information in the Emacs process, aside from files that have
been saved, is lost when the Emacs is killed. Because killing Emacs
inadvertently can lose a lot of work, Emacs queries for confirmation
before actually terminating if you have buffers that need saving or
subprocesses that are running. This is done in the function
save-buffers-kill-emacs.
save-buffers-kill-emacs
calls the functions in the list kill-emacs-query-functions, in
order of appearance, with no arguments. These functions can ask for
additional confirmation from the user. If any of them returns
nil, Emacs is not killed.
save-buffers-kill-emacs is
finished with all file saving and confirmation, it runs the functions in
this hook.
Suspending Emacs means stopping Emacs temporarily and returning
control to its superior process, which is usually the shell. This
allows you to resume editing later in the same Emacs process, with the
same buffers, the same kill ring, the same undo history, and so on. To
resume Emacs, use the appropriate command in the parent shell--most
likely fg.
Some operating systems do not support suspension of jobs; on these systems, "suspension" actually creates a new shell temporarily as a subprocess of Emacs. Then you would exit the shell to return to Emacs.
Suspension is not useful with window systems, because the Emacs job may not have a parent that can resume it again, and in any case you can give input to some other job such as a shell merely by moving to a different window. Therefore, suspending is not allowed when Emacs is using a window system.
suspend-emacs
returns nil to its caller in Lisp.
If string is non-nil, its characters are sent to be read
as terminal input by Emacs's superior shell. The characters in
string are not echoed by the superior shell; only the results
appear.
Before suspending, suspend-emacs runs the normal hook
suspend-hook.
After the user resumes Emacs, suspend-emacs runs the normal hook
suspend-resume-hook. See section Hooks.
The next redisplay after resumption will redraw the entire screen,
unless the variable no-redraw-on-reenter is non-nil
(see section Refreshing the Screen).
In the following example, note that `pwd' is not echoed after Emacs is suspended. But it is read and executed by the shell.
(suspend-emacs)
=> nil
(add-hook 'suspend-hook
(function (lambda ()
(or (y-or-n-p
"Really suspend? ")
(error "Suspend cancelled")))))
=> (lambda nil
(or (y-or-n-p "Really suspend? ")
(error "Suspend cancelled")))
(add-hook 'suspend-resume-hook
(function (lambda () (message "Resumed!"))))
=> (lambda nil (message "Resumed!"))
(suspend-emacs "pwd")
=> nil
---------- Buffer: Minibuffer ----------
Really suspend? y
---------- Buffer: Minibuffer ----------
---------- Parent Shell ----------
lewis@slug[23] % /user/lewis/manual
lewis@slug[24] % fg
---------- Echo Area ----------
Resumed!
Emacs provides access to variables in the operating system environment through various functions. These variables include the name of the system, the user's UID, and so on.
string-match.
alpha-vms
aix-v3
berkeley-unix
dgux
gnu
gnu/linux
hpux
irix
ms-dos
next-mach
rtu
unisoft-unix
usg-unix-v
vax-vms
windows-nt
xenix
We do not wish to add new symbols to make finer distinctions unless it
is absolutely necessary! In fact, we hope to eliminate some of these
alternatives in the future. We recommend using
system-configuration to distinguish between different operating
systems.
(system-name)
=> "www.gnu.org"
The symbol system-name is a variable as well as a function. In
fact, the function returns whatever value the variable
system-name currently holds. Thus, you can set the variable
system-name in case Emacs is confused about the name of your
system. The variable is also useful for constructing frame titles
(see section Frame Titles).
nil, it is used instead of
system-name for purposes of generating email addresses. For
example, it is used when constructing the default value of
user-mail-address. See section User Identification. (Since this is
done when Emacs starts up, the value actually used is the one saved when
Emacs was dumped. See section Building Emacs.)
process-environment.
(getenv "USER")
=> "lewis"
lewis@slug[10] % printenv
PATH=.:/user/lewis/bin:/usr/bin:/usr/local/bin
USER=lewis
TERM=ibmapa16
SHELL=/bin/csh
HOME=/user/lewis
process-environment; binding that
variable with let is also reasonable practice.
getenv and setenv work by means
of this variable.
process-environment
=> ("l=/usr/stanford/lib/gnuemacs/lisp"
"PATH=.:/user/lewis/bin:/usr/class:/nfsusr/local/bin"
"USER=lewis"
"TERM=ibmapa16"
"SHELL=/bin/csh"
"HOME=/user/lewis")
":" for Unix and GNU systems, and ";" for MS-DOS
and Windows NT.
nil if that directory cannot be determined.
nil, this is a directory within which to look for the
`lib-src' and `etc' subdirectories. This is non-nil
when Emacs can't find those directories in their standard installed
locations, but can find them in a directory related somehow to the one
containing the Emacs executable.
By default, the values are integers that are 100 times the system load
averages, which indicate the average number of processes trying to run.
If use-float is non-nil, then they are returned
as floating point numbers and without multiplying by 100.
(load-average)
=> (169 48 36)
(load-average t)
=> (1.69 0.48 0.36)
lewis@rocky[5] % uptime
11:55am up 1 day, 19:37, 3 users,
load average: 1.69, 0.48, 0.36
t or nil, indicating whether the
privilege is to be turned on or off. Its default is nil. The
function returns t if successful, nil otherwise.
If the third argument, getprv, is non-nil, setprv
does not change the privilege, but returns t or nil
indicating whether the privilege is currently enabled.
nil if none. The value reflects command line options such as
`-q' or `-u user'.
Lisp packages that load files of customizations, or any other sort of
user profile, should obey this variable in deciding where to find it.
They should load the profile of the user name found in this variable.
If init-file-user is nil, meaning that the `-q'
option was used, then Lisp packages should not load any customization
files or user profile.
LOGNAME
is set, that value is used. Otherwise, if the environment variable
USER is set, that value is used. Otherwise, the value is based
on the effective UID, not the real UID.
If you specify uid, the value is the user name that corresponds to uid (which should be an integer).
(user-login-name)
=> "lewis"
LOGNAME and USER.
NAME, if that is set.
(user-full-name)
=> "Bil Lewis"
If uid is non-nil, then it should be an integer, a user-id,
or a string, a login name. Then user-full-name returns the full
name corresponding to that user-id or login name.
The symbols user-login-name, user-real-login-name and
user-full-name are variables as well as functions. The functions
return the same values that the variables hold. These variables allow
you to "fake out" Emacs by telling the functions what to return. The
variables are also useful for constructing frame titles (see section Frame Titles).
(user-real-uid)
=> 19
This section explains how to determine the current time and the time zone.
substring to extract pieces of it. It is wise to count the
characters from the beginning of the string rather than from the end, as
additional information may some day be added at the end.
The argument time-value, if given, specifies a time to format
instead of the current time. The argument should be a list whose first
two elements are integers. Thus, you can use times obtained from
current-time (see below) and from file-attributes
(see section Other Information about Files).
(current-time-string)
=> "Wed Oct 14 22:21:05 1987"
(high low microsec). The integers
high and low combine to give the number of seconds since
0:00 January 1, 1970, which is
The third element, microsec, gives the microseconds since the start of the current second (or 0 for systems that return time only on the resolution of a second).
The first two elements can be compared with file time values such as you
get with the function file-attributes. See section Other Information about Files.
The value has the form (offset name). Here
offset is an integer giving the number of seconds ahead of UTC
(east of Greenwich). A negative value means west of Greenwich. The
second element, name is a string giving the name of the time
zone. Both elements change when daylight savings time begins or ends;
if the user has specified a time zone that does not use a seasonal time
adjustment, then the value is constant through time.
If the operating system doesn't supply all the information necessary to
compute the value, both elements of the list are nil.
The argument time-value, if given, specifies a time to analyze
instead of the current time. The argument should be a cons cell
containing two integers, or a list whose first two elements are
integers. Thus, you can use times obtained from current-time
(see above) and from file-attributes (see section Other Information about Files).
These functions convert time values (lists of two or three integers)
to strings or to calendrical information. There is also a function to
convert calendrical information to a time value. You can get time
values from the functions current-time (see section Time of Day) and
file-attributes (see section Other Information about Files).
Many operating systems are limited to time values that contain 32 bits of information; these systems typically handle only the times from 1901-12-13 20:45:52 UTC through 2038-01-19 03:14:07 UTC. However, some operating systems have larger time values, and can represent times far in the past or future.
Time conversion functions always use the Gregorian calendar, even for dates before the Gregorian calendar was introduced. Year numbers count the number of years since the year 1 B.C., and do not skip zero as traditional Gregorian years do; for example, the year number -37 represents the Gregorian year 38 B.C.
You can also specify the field width and type of padding for any of
these `%'-sequences. This works as in printf: you write
the field width as digits in the middle of a `%'-sequences. If you
start the field width with `0', it means to pad with zeros. If you
start the field width with `_', it means to pad with spaces.
For example, `%S' specifies the number of seconds since the minute; `%03S' means to pad this with zeros to 3 positions, `%_3S' to pad with spaces to 3 positions. Plain `%3S' pads with zeros, because that is how `%S' normally pads to two positions.
(seconds minutes hour day month year dow dst zone)
Here is what the elements mean:
t if daylight savings time is effect, otherwise nil.
Common Lisp Note: Common Lisp has different meanings for dow and zone.
decode-time. It converts seven
items of calendrical data into a time value. For the meanings of the
arguments, see the table above under decode-time.
Year numbers less than 100 are treated just like other year numbers. If
you want them to stand for years above 1900, you must alter them yourself
before you call encode-time.
The optional argument zone defaults to the current time zone and
its daylight savings time rules. If specified, it can be either a list
(as you would get from current-time-zone), a string as in the
TZ environment variable, or an integer (as you would get from
decode-time). The specified zone is used without any further
alteration for daylight savings time.
If you pass more than seven arguments to encode-time, the first
six are used as seconds through year, the last argument is
used as zone, and the arguments in between are ignored. This
feature makes it possible to use the elements of a list returned by
decode-time as the arguments to encode-time, like this:
(apply 'encode-time (decode-time ...))
You can perform simple date arithmetic by using out-of-range values for the sec, minute, hour, day, and month arguments; for example, day 0 means the day preceding the given month.
The operating system puts limits on the range of possible time values; if you try to encode a time that is out of range, an error results.
You can set up a timer to call a function at a specified future time or after a certain length of idleness.
Emacs cannot run timers at any arbitrary point in a Lisp program; it
can run them only when Emacs could accept output from a subprocess:
namely, while waiting or inside certain primitive functions such as
sit-for or read-event which can wait. Therefore, a
timer's execution may be delayed if Emacs is busy. However, the time of
execution is very precise if Emacs is idle.
Absolute times may be specified in a wide variety of formats; this function tries to accept all the commonly used date formats. Valid formats include these two,
year-month-day hour:min:sec timezone hour:min:sec timezone month/day/year
where in both examples all fields are numbers; the format that
current-time-string returns is also allowed, and many others
as well.
To specify a relative time, use numbers followed by units. For example:
If time is a number (integer or floating point), that specifies a relative time measured in seconds.
The argument repeat specifies how often to repeat the call. If
repeat is nil, there are no repetitions; function is
called just once, at time. If repeat is a number, it
specifies a repetition period measured in seconds.
In most cases, repeat has no effect on when first call
takes place---time alone specifies that. There is one exception:
if time is t, then the timer runs whenever the time is a
multiple of repeat seconds after the epoch. This is useful for
functions like display-time.
The function run-at-time returns a timer value that identifies
the particular scheduled future action. You can use this value to call
cancel-timer (see below).
with-timeout returns
the value of the last form in body. If, however, the execution of
body is cut short by the timeout, then with-timeout
executes all the timeout-forms and returns the value of the last
of them.
This macro works by setting a timer to run after seconds seconds. If body finishes before that time, it cancels the timer. If the timer actually runs, it terminates execution of body, then executes timeout-forms.
Since timers can run within a Lisp program only when the program calls a
primitive that can wait, with-timeout cannot stop executing
body while it is in the midst of a computation--only when it
calls one of those primitives. So use with-timeout only with a
body that waits for input, not one that does a long computation.
The function y-or-n-p-with-timeout provides a simple way to use
a timer to avoid waiting too long for an answer. See section Yes-or-No Queries.
If repeat is nil, the timer runs just once, the first time
Emacs remains idle for a long enough time. More often repeat is
non-nil, which means to run the timer each time Emacs
remains idle for secs seconds.
The function run-with-idle-timer returns a timer value which you
can use in calling cancel-timer (see below).
Emacs becomes "idle" when it starts waiting for user input, and it remains idle until the user provides some input. If a timer is set for five seconds of idleness, it runs approximately five seconds after Emacs first became idle. Even if its repeat is true, this timer will not run again as long as Emacs remains idle, because the duration of idleness will continue to increase and will not go down to five seconds again.
Emacs can do various things while idle: garbage collect, autosave or handle data from a subprocess. But these interludes during idleness do not interfere with idle timers, because they do not reset the clock of idleness to zero. An idle timer set for 600 seconds will run when ten minutes have elapsed since the last user command was finished, even if subprocess output has been accepted thousands of times within those ten minutes, even if there have been garbage collections and autosaves.
When the user supplies input, Emacs becomes non-idle while executing the input. Then it becomes idle again, and all the idle timers that are set up to repeat will subsequently run another time, one by one.
run-at-time or run-with-idle-timer.
This cancels the effect of that call to run-at-time; the arrival
of the specified time will not cause anything special to happen.
This section describes functions and variables for recording or manipulating terminal input. See section Emacs Display, for related functions.
nil, then it uses CBREAK mode. The default setting is
system dependent. Some systems always use CBREAK mode regardless
of what is specified.
When Emacs communicates directly with X, it ignores this argument and uses interrupts if that is the way it knows how to communicate.
If flow is non-nil, then Emacs uses XON/XOFF
(C-q, C-s) flow control for output to the terminal. This
has no effect except in CBREAK mode. See section Flow Control.
The argument meta controls support for input character codes
above 127. If meta is t, Emacs converts characters with
the 8th bit set into Meta characters. If meta is nil,
Emacs disregards the 8th bit; this is necessary when the terminal uses
it as a parity bit. If meta is neither t nor nil,
Emacs uses all 8 bits of input unchanged. This is good for terminals
that use 8-bit character sets.
If quit-char is non-nil, it specifies the character to
use for quitting. Normally this character is C-g.
See section Quitting.
The current-input-mode function returns the input mode settings
Emacs is currently using.
set-input-mode,
of the form (interrupt flow meta quit) in
which:
nil when Emacs is using interrupt-driven input. If
nil, Emacs is using CBREAK mode.
nil if Emacs uses XON/XOFF (C-q, C-s)
flow control for output to the terminal. This value is meaningful only
when interrupt is nil.
t if Emacs treats the eighth bit of input characters as
the meta bit; nil means Emacs clears the eighth bit of every
input character; any other value means Emacs uses all eight bits as the
basic character code.
This section describes features for translating input events into
other input events before they become part of key sequences. These
features apply to each event in the order they are described here: each
event is first modified according to extra-keyboard-modifiers,
then translated through keyboard-translate-table (if applicable),
and finally decoded with the specified keyboard coding system. If it is
being read as part of a key sequence, it is then added to the sequence
being read; then subsequences containing it are checked first with
function-key-map and then with key-translation-map.
Each time the user types a keyboard key, it is altered as if the modifier keys specified in the bit mask were held down.
When using a window system, the program can "press" any of the modifier keys in this way. Otherwise, only the CTL and META keys can be virtually pressed.
nil.
If keyboard-translate-table is a char-table, then each character
read from the keyboard is looked up in this character. If the value
found there is non-nil, then it is used instead of the
actual input character.
In the example below, we set keyboard-translate-table to a
char-table. Then we fill it in to swap the characters C-s and
C-\ and the characters C-q and C-^. Subsequently,
typing C-\ has all the usual effects of typing C-s, and vice
versa. (See section Flow Control for more information on this subject.)
(defun evade-flow-control ()
"Replace C-s with C-\ and C-q with C-^."
(interactive)
(setq keyboard-translate-table
(make-char-table 'keyboard-translate-table nil))
;; Swap C-s and C-\.
(aset keyboard-translate-table ?\034 ?\^s)
(aset keyboard-translate-table ?\^s ?\034)
;; Swap C-q and C-^.
(aset keyboard-translate-table ?\036 ?\^q)
(aset keyboard-translate-table ?\^q ?\036))
Note that this translation is the first thing that happens to a
character after it is read from the terminal. Record-keeping features
such as recent-keys and dribble files record the characters after
translation.
keyboard-translate-table to translate
character code from into character code to. It creates
the keyboard translate table if necessary.
The remaining translation features translate subsequences of key
sequences being read. They are implemented in read-key-sequence
and have no effect on input read with read-event.
If function-key-map "binds" a key sequence k to a vector
v, then when k appears as a subsequence anywhere in a
key sequence, it is replaced with the events in v.
For example, VT100 terminals send ESC O P when the
keypad PF1 key is pressed. Therefore, we want Emacs to translate
that sequence of events into the single event pf1. We accomplish
this by "binding" ESC O P to [pf1] in
function-key-map, when using a VT100.
Thus, typing C-c PF1 sends the character sequence C-c
ESC O P; later the function read-key-sequence translates
this back into C-c PF1, which it returns as the vector
[?\C-c pf1].
Entries in function-key-map are ignored if they conflict with
bindings made in the minor mode, local, or global keymaps. The intent
is that the character sequences that function keys send should not have
command bindings in their own right--but if they do, the ordinary
bindings take priority.
The value of function-key-map is usually set up automatically
according to the terminal's Terminfo or Termcap entry, but sometimes
those need help from terminal-specific Lisp files. Emacs comes with
terminal-specific files for many common terminals; their main purpose is
to make entries in function-key-map beyond those that can be
deduced from Termcap and Terminfo. See section Terminal-Specific Initialization.
function-key-map
to translate input events into other events. It differs from
function-key-map in two ways:
key-translation-map goes to work after function-key-map is
finished; it receives the results of translation by
function-key-map.
key-translation-map overrides actual key bindings. For example,
if C-x f has a binding in key-translation-map, that
translation takes effect even though C-x f also has a key binding
in the global map.
The intent of key-translation-map is for users to map one
character set to another, including ordinary characters normally bound
to self-insert-command.
You can use function-key-map or key-translation-map for
more than simple aliases, by using a function, instead of a key
sequence, as the "translation" of a key. Then this function is called
to compute the translation of that key.
The key translation function receives one argument, which is the prompt
that was specified in read-key-sequence---or nil if the
key sequence is being read by the editor command loop. In most cases
you can ignore the prompt value.
If the function reads input itself, it can have the effect of altering the event that follows. For example, here's how to define C-c h to turn the character that follows into a Hyper character:
(defun hyperify (prompt)
(let ((e (read-event)))
(vector (if (numberp e)
(logior (lsh 1 24) e)
(if (memq 'hyper (event-modifiers e))
e
(add-event-modifier "H-" e))))))
(defun add-event-modifier (string e)
(let ((symbol (if (symbolp e) e (car e))))
(setq symbol (intern (concat string
(symbol-name symbol))))
(if (symbolp e)
symbol
(cons symbol (cdr e)))))
(define-key function-key-map "\C-ch" 'hyperify)
Finally, if you have enabled keyboard character set decoding using
set-keyboard-coding-system, decoding is done after the
translations listed above. See section Specifying a Coding System for One Operation. In future
Emacs versions, character set decoding may be done before the other
translations.
You close the dribble file by calling this function with an argument
of nil.
This function is normally used to record the input necessary to trigger an Emacs bug, for the sake of a bug report.
(open-dribble-file "~/dribble")
=> nil
See also the open-termscript function (see section Terminal Output).
The terminal output functions send output to the terminal or keep
track of output sent to the terminal. The variable baud-rate
tells you what Emacs thinks is the output speed of the terminal.
The value is measured in baud.
If you are running across a network, and different parts of the
network work at different baud rates, the value returned by Emacs may be
different from the value used by your local terminal. Some network
protocols communicate the local terminal speed to the remote machine, so
that Emacs and other programs can get the proper value, but others do
not. If Emacs has the wrong value, it makes decisions that are less
than optimal. To fix the problem, set baud-rate.
baud-rate.
One use of this function is to define function keys on terminals that have downloadable function key definitions. For example, this is how on certain terminals to define function key 4 to move forward four characters (by transmitting the characters C-u C-f to the computer):
(send-string-to-terminal "\eF4\^U\^F")
=> nil
nil. Termscript files are useful for investigating problems
where Emacs garbles the screen, problems that are due to incorrect
Termcap entries or to undesirable settings of terminal options more
often than to actual Emacs bugs. Once you are certain which characters
were actually output, you can determine reliably whether they correspond
to the Termcap specifications in use.
See also open-dribble-file in section Terminal Input.
(open-termscript "../junk/termscript")
=> nil
To define system-specific X11 keysyms, set the variable
system-key-alist.
(code
. symbol), where code is the numeric keysym code (not
including the "vendor specific" bit,
and symbol is the name for the function key.
For example (168 . mute-acute) defines a system-specific key used
by HP X servers whose numeric code is
+ 168.
It is not crucial to exclude from the alist the keysyms of other X servers; those do no harm, as long as they don't conflict with the ones used by the X server actually in use.
The variable is always local to the current terminal, and cannot be buffer-local. See section Multiple Displays.
This section attempts to answer the question "Why does Emacs use flow-control characters in its command character set?" For a second view on this issue, read the comments on flow control in the `emacs/INSTALL' file from the distribution; for help with Termcap entries and DEC terminal concentrators, see `emacs/etc/TERMS'.
At one time, most terminals did not need flow control, and none used
C-s and C-q for flow control. Therefore, the choice of
C-s and C-q as command characters for searching and quoting
was natural and uncontroversial. With so many commands needing key
assignments, of course we assigned meanings to nearly all ASCII
control characters.
Later, some terminals were introduced which required these characters for flow control. They were not very good terminals for full-screen editing, so Emacs maintainers ignored them. In later years, flow control with C-s and C-q became widespread among terminals, but by this time it was usually an option. And the majority of Emacs users, who can turn flow control off, did not want to switch to less mnemonic key bindings for the sake of flow control.
So which usage is "right"---Emacs's or that of some terminal and concentrator manufacturers? This question has no simple answer.
One reason why we are reluctant to cater to the problems caused by C-s and C-q is that they are gratuitous. There are other techniques (albeit less common in practice) for flow control that preserve transparency of the character stream. Note also that their use for flow control is not an official standard. Interestingly, on the model 33 teletype with a paper tape punch (around 1970), C-s and C-q were sent by the computer to turn the punch on and off!
As window systems and PC terminal emulators replace character-only
terminals, the flow control problem is gradually disappearing. For the
mean time, Emacs provides a convenient way of enabling flow control if
you want it: call the function enable-flow-control.
keyboard-translate-table (see section Translating Input Events).
You can use the function enable-flow-control-on in your
`.emacs' file to enable flow control automatically on certain
terminal types.
(enable-flow-control-on "vt200" "vt300" "vt101" "vt131")
Here is how enable-flow-control does its job:
(set-input-mode nil t).
keyboard-translate-table to translate C-\ and
C-^ into C-s and C-q. Except at its very
lowest level, Emacs never knows that the characters typed were anything
but C-s and C-q, so you can in effect type them as C-\
and C-^ even when they are input for other commands.
See section Translating Input Events.
If the terminal is the source of the flow control characters, then once
you enable kernel flow control handling, you probably can make do with
less padding than normal for that terminal. You can reduce the amount
of padding by customizing the Termcap entry. You can also reduce it by
setting baud-rate to a smaller value so that Emacs uses a smaller
speed when calculating the padding needed. See section Terminal Output.
The command line option `-batch' causes Emacs to run noninteractively. In this mode, Emacs does not read commands from the terminal, it does not alter the terminal modes, and it does not expect to be outputting to an erasable screen. The idea is that you specify Lisp programs to run; when they are finished, Emacs should exit. The way to specify the programs to run is with `-l file', which loads the library named file, and `-f function', which calls function with no arguments.
Any Lisp program output that would normally go to the echo area,
either using message or using prin1, etc., with t
as the stream, goes instead to Emacs's standard error descriptor when
in batch mode. Thus, Emacs behaves much like a noninteractive
application program. (The echo area output that Emacs itself normally
generates, such as command echoing, is suppressed entirely.)
nil when Emacs is running in batch mode.
This chapter describes a number of features related to the display that Emacs presents to the user.
The function redraw-frame redisplays the entire contents of a
given frame (see section Frames).
Even more powerful is redraw-display:
Processing user input takes absolute priority over redisplay. If you call these functions when input is available, they do nothing immediately, but a full redisplay does happen eventually--after all the input has been processed.
Normally, suspending and resuming Emacs also refreshes the screen. Some terminal emulators record separate contents for display-oriented programs such as Emacs and for ordinary sequential display. If you are using such a terminal, you might want to inhibit the redisplay on resumption.
nil means there is no need
to redraw, nil means redrawing is needed. The default is nil.
When a line of text extends beyond the right edge of a window, the line can either be continued on the next screen line, or truncated to one screen line. The additional screen lines used to display a long text line are called continuation lines. Normally, a `$' in the rightmost column of the window indicates truncation; a `\' on the rightmost column indicates a line that "wraps" onto the next line, which is also called continuing the line. (The display table can specify alternative indicators; see section Display Tables.)
Note that continuation is different from filling; continuation happens on the screen only, not in the buffer contents, and it breaks a line precisely at the right margin, not at a word boundary. See section Filling.
nil, which
specifies continuation. If the value is non-nil, then these
lines are truncated.
If the variable truncate-partial-width-windows is non-nil,
then truncation is always used for side-by-side windows (within one
frame) regardless of the value of truncate-lines.
truncate-lines, for
buffers that do not have buffer-local values for it.
nil, these lines are truncated; otherwise,
truncate-lines says what to do with them.
When horizontal scrolling (see section Horizontal Scrolling) is in use in a window, that forces truncation.
You can override the glyphs that indicate continuation or truncation using the display table; see section Display Tables.
If your buffer contains very long lines, and you use
continuation to display them, just thinking about them can make Emacs
redisplay slow. The column computation and indentation functions also
become slow. Then you might find it advisable to set
cache-long-line-scans to t.
nil, various indentation and motion
functions, and Emacs redisplay, cache the results of scanning the
buffer, and consult the cache to avoid rescanning regions of the buffer
unless they are modified.
Turning on the cache slows down processing of short lines somewhat.
This variable is automatically buffer-local in every buffer.
The echo area is used for displaying messages made with the
message primitive, and for echoing keystrokes. It is not the
same as the minibuffer, despite the fact that the minibuffer appears
(when active) in the same place on the screen as the echo area. The
GNU Emacs Manual specifies the rules for resolving conflicts
between the echo area and the minibuffer for use of that screen space
(see section `The Minibuffer' in The GNU Emacs Manual).
Error messages appear in the echo area; see section Errors.
You can write output in the echo area by using the Lisp printing
functions with t as the stream (see section Output Functions), or as
follows:
printf control
string. See format in section Conversion of Characters and Strings, for the details
on the conversion specifications. message returns the
constructed string.
In batch mode, message prints the message text on the standard
error stream, followed by a newline.
If string is nil, message clears the echo area. If
the minibuffer is active, this brings the minibuffer contents back onto
the screen immediately.
(message "Minibuffer depth is %d."
(minibuffer-depth))
-| Minibuffer depth is 0.
=> "Minibuffer depth is 0."
---------- Echo Area ----------
Minibuffer depth is 0.
---------- Echo Area ----------
message, but may display it
in a dialog box instead of the echo area. If this function is called in
a command that was invoked using the mouse--more precisely, if
last-nonmenu-event (see section Information from the Command Loop) is either
nil or a list--then it uses a dialog box or pop-up menu to
display the message. Otherwise, it uses the echo area. (This is the
same criterion that y-or-n-p uses to make a similar decision; see
section Yes-or-No Queries.)
You can force use of the mouse or of the echo area by binding
last-nonmenu-event to a suitable value around the call.
message, but uses a dialog
box (or a pop-up menu) whenever that is possible. If it is impossible
to use a dialog box or pop-up menu, because the terminal does not
support them, then message-box uses the echo area, like
message.
nil if there is none.
nil, then the cursor
appears at the end of the message. Otherwise, the cursor appears at
point--not in the echo area at all.
The value is normally nil; Lisp programs bind it to t
for brief periods of time.
(message nil) or for any other reason.
Almost all the messages displayed in the echo area are also recorded in the `*Messages*' buffer.
t means there is no limit on how many lines to
keep. The value nil disables message logging entirely. Here's
how to display a message and prevent it from being logged:
(let (message-log-max) (message ...))
If the value is zero, then command input is not echoed.
You can make characters invisible, so that they do not appear on
the screen, with the invisible property. This can be either a
text property (see section Text Properties) or a property of an overlay
(see section Overlays).
In the simplest case, any non-nil invisible property makes
a character invisible. This is the default case--if you don't alter
the default value of buffer-invisibility-spec, this is how the
invisible property works.
More generally, you can use the variable buffer-invisibility-spec
to control which values of the invisible property make text
invisible. This permits you to classify the text into different subsets
in advance, by giving them different invisible values, and
subsequently make various subsets visible or invisible by changing the
value of buffer-invisibility-spec.
Controlling visibility with buffer-invisibility-spec is
especially useful in a program to display the list of entries in a data
base. It permits the implementation of convenient filtering commands to
view just a part of the entries in the data base. Setting this variable
is very fast, much faster than scanning all the text in the buffer
looking for properties to change.
invisible properties
actually make a character invisible.
t
invisible property is
non-nil. This is the default.
invisible property fits any one of these criteria,
the character is invisible. The list can have two kinds of elements:
atom
invisible property value
is atom or if it is a list with atom as a member.
(atom . t)
invisible property value
is atom or if it is a list with atom as a member.
Moreover, if this character is at the end of a line and is followed
by a visible newline, it displays an ellipsis.
Two functions are specifically provided for adding elements to
buffer-invisibility-spec and removing elements from it.
buffer-invisibility-spec
(if it is not already present in that list).
buffer-invisibility-spec.
One convention about the use of buffer-invisibility-spec is
that a major mode should use the mode's own name as an element of
buffer-invisibility-spec and as the value of the invisible
property:
;; If you want to display an ellipsis:
(add-to-invisibility-spec '(my-symbol . t))
;; If you don't want ellipsis:
(add-to-invisibility-spec 'my-symbol)
(overlay-put (make-overlay beginning end)
'invisible 'my-symbol)
;; When done with the overlays:
(remove-from-invisibility-spec '(my-symbol . t))
;; Or respectively:
(remove-from-invisibility-spec 'my-symbol)
Ordinarily, commands that operate on text or move point do not care
whether the text is invisible. The user-level line motion commands
explicitly ignore invisible newlines if
line-move-ignore-invisible is non-nil, but only because
they are explicitly programmed to do so.
Incremental search can make invisible overlays visible temporarily
and/or permanently when a match includes invisible text. To enable
this, the overlay should have a non-nil
isearch-open-invisible property. The property value should be a
function to be called with the overlay as an argument. This function
should make the overlay visible permanently; it is used when the match
overlaps the overlay on exit from the search.
During the search, such overlays are made temporarily visible by
temporarily modifying their invisible and intangible properties. If you
want this to be done differently for a certain overlay, give it an
isearch-open-invisible-temporary property which is a function.
The function is called with two arguments: the first is the overlay, and
the second is t to make the overlay visible, or nil to
make it invisible again.
Selective display refers to a pair of related features for hiding certain lines on the screen.
The first variant, explicit selective display, is designed for use in a Lisp program: it controls which lines are hidden by altering the text. The invisible text feature (see section Invisible Text) has partially replaced this feature.
In the second variant, the choice of lines to hide is made automatically based on indentation. This variant is designed to be a user-level feature.
The way you control explicit selective display is by replacing a newline (control-j) with a carriage return (control-m). The text that was formerly a line following that newline is now invisible. Strictly speaking, it is temporarily no longer a line at all, since only newlines can separate lines; it is now part of the previous line.
Selective display does not directly affect editing commands. For
example, C-f (forward-char) moves point unhesitatingly into
invisible text. However, the replacement of newline characters with
carriage return characters affects some editing commands. For example,
next-line skips invisible lines, since it searches only for
newlines. Modes that use selective display can also define commands
that take account of the newlines, or that make parts of the text
visible or invisible.
When you write a selectively displayed buffer into a file, all the control-m's are output as newlines. This means that when you next read in the file, it looks OK, with nothing invisible. The selective display effect is seen only within Emacs.
selective-display is t, then any portion
of a line that follows a control-m is not displayed. This is explicit
selective display.
selective-display is a positive integer, then
lines that start with more than that many columns of indentation are not
displayed.
When some portion of a buffer is invisible, the vertical movement
commands operate as if that portion did not exist, allowing a single
next-line command to skip any number of invisible lines.
However, character movement commands (such as forward-char) do
not skip the invisible portion, and it is possible (if tricky) to insert
or delete text in an invisible portion.
In the examples below, we show the display appearance of the
buffer foo, which changes with the value of
selective-display. The contents of the buffer do not
change.
(setq selective-display nil)
=> nil
---------- Buffer: foo ----------
1 on this column
2on this column
3n this column
3n this column
2on this column
1 on this column
---------- Buffer: foo ----------
(setq selective-display 2)
=> 2
---------- Buffer: foo ----------
1 on this column
2on this column
2on this column
1 on this column
---------- Buffer: foo ----------
nil, then Emacs displays
`...' at the end of a line that is followed by invisible text.
This example is a continuation of the previous one.
(setq selective-display-ellipses t)
=> t
---------- Buffer: foo ----------
1 on this column
2on this column ...
2on this column
1 on this column
---------- Buffer: foo ----------
You can use a display table to substitute other text for the ellipsis (`...'). See section Display Tables.
The overlay arrow is useful for directing the user's attention to a particular line in a buffer. For example, in the modes used for interface to debuggers, the overlay arrow indicates the line of code about to be executed.
nil if the arrow feature is not in use.
The overlay string is displayed only in the buffer that this marker points into. Thus, only one buffer can have an overlay arrow at any given time.
You can do a similar job by creating an overlay with a
before-string property. See section Overlay Properties.
Temporary displays are used by Lisp programs to put output into a buffer and then present it to the user for perusal rather than for editing. Many help commands use this feature.
The string buffer-name specifies the temporary buffer, which
need not already exist. The argument must be a string, not a buffer.
The buffer is erased initially (with no questions asked), and it is
marked as unmodified after with-output-to-temp-buffer exits.
with-output-to-temp-buffer binds standard-output to the
temporary buffer, then it evaluates the forms in forms. Output
using the Lisp output functions within forms goes by default to
that buffer (but screen display and messages in the echo area, although
they are "output" in the general sense of the word, are not affected).
See section Output Functions.
The value of the last form in forms is returned.
---------- Buffer: foo ----------
This is the contents of foo.
---------- Buffer: foo ----------
(with-output-to-temp-buffer "foo"
(print 20)
(print standard-output))
=> #<buffer foo>
---------- Buffer: foo ----------
20
#<buffer foo>
---------- Buffer: foo ----------
nil, with-output-to-temp-buffer
calls it as a function to do the job of displaying a help buffer. The
function gets one argument, which is the buffer it should display.
It is a good idea for this function to run temp-buffer-show-hook
just as with-output-to-temp-buffer normally would, inside of
save-window-excursion and with the chosen window and buffer
selected.
with-output-to-temp-buffer after
displaying the help buffer. When the hook runs, the help buffer is
current, and the window it was displayed in is selected.
The momentary display remains until the next input event. If the next
input event is char, momentary-string-display ignores it
and returns. Otherwise, that event remains buffered for subsequent use
as input. Thus, typing char will simply remove the string from
the display, while typing (say) C-f will remove the string from
the display and later (presumably) move point forward. The argument
char is a space by default.
The return value of momentary-string-display is not meaningful.
If the string string does not contain control characters, you can
do the same job in a more general way by creating (and then subsequently
deleting) an overlay with a before-string property.
See section Overlay Properties.
If message is non-nil, it is displayed in the echo area
while string is displayed in the buffer. If it is nil, a
default message says to type char to continue.
In this example, point is initially located at the beginning of the second line:
---------- Buffer: foo ---------- This is the contents of foo. -!-Second line. ---------- Buffer: foo ---------- (momentary-string-display "**** Important Message! ****" (point) ?\r "Type RET when done reading") => t ---------- Buffer: foo ---------- This is the contents of foo. **** Important Message! ****Second line. ---------- Buffer: foo ---------- ---------- Echo Area ---------- Type RET when done reading ---------- Echo Area ----------
You can use overlays to alter the appearance of a buffer's text on the screen, for the sake of presentation features. An overlay is an object that belongs to a particular buffer, and has a specified beginning and end. It also has properties that you can examine and set; these affect the display of the text within the overlay.
Overlay properties are like text properties in that the properties that alter how a character is displayed can come from either source. But in most respects they are different. Text properties are considered a part of the text; overlays are specifically considered not to be part of the text. Thus, copying text between various buffers and strings preserves text properties, but does not try to preserve overlays. Changing a buffer's text properties marks the buffer as modified, while moving an overlay or changing its properties does not. Unlike text property changes, overlay changes are not recorded in the buffer's undo list. See section Text Properties, for comparison.
priority
priority value is larger takes priority over the
other, and its face attributes override the face attributes of the lower
priority overlay.
Currently, all overlays take priority over text properties. Please
avoid using negative priority values, as we have not yet decided just
what they should mean.
window
window property is non-nil, then the overlay
applies only on that window.
category
category property, we call it the
category of the overlay. It should be a symbol. The properties
of the symbol serve as defaults for the properties of the overlay.
face
(foreground-color . color-name) or (background-color
. color-name). These elements specify just the foreground color
or just the background color; therefore, there is no need to create a
face for each color that you want to use.
mouse-face
face when the mouse is within
the range of the overlay.
modification-hooks
nil, and the beginning and end of the text range to be
modified.
When called after a change, each function receives five arguments: the
overlay, t, the beginning and end of the text range just
modified, and the length of the pre-change text replaced by that range.
(For an insertion, the pre-change length is zero; for a deletion, that
length is the number of characters deleted, and the post-change
beginning and end are equal.)
insert-in-front-hooks
modification-hooks functions.
insert-behind-hooks
modification-hooks functions.
invisible
invisible property can make the text in the overlay
invisible, which means that it does not appear on the screen.
See section Invisible Text, for details.
intangible
intangible property on an overlay works just like the
intangible text property. See section Properties with Special Meanings, for details.
isearch-open-invisible
isearch-open-invisible-temporary
before-string
after-string
evaporate
nil, the overlay is deleted automatically
if it ever becomes empty (i.e., if it spans no characters).
local-map
nil, it specifies a keymap for a portion
of the text. The property's value replaces the buffer's local map, when
the character after point is within the overlay. See section Active Keymaps.
These are the functions for reading and writing the properties of an overlay.
category property which is a
symbol, that symbol's prop property is used. Otherwise, the value
is nil.
See also the function get-char-property which checks both
overlay properties and text properties for a given character.
See section Examining Text Properties.
This section describes the functions to create, delete and move overlays, and to examine their contents.
The arguments front-advance and rear-advance specify the insertion type for the start of the overlay and for the end of the overlay. See section Marker Insertion Types.
A deleted overlay is not permanently useless. You can give it
a new buffer position by calling move-overlay.
The return value is overlay.
This is the only valid way to change the endpoints of an overlay. Do not try modifying the markers in the overlay by hand, as that fails to update other vital data structures and can cause some overlays to be "lost".
Since not all characters have the same width, these functions let you check the width of a character. See section Indentation Primitives, and section Motion by Screen Lines, for related functions.
If string does not reach width, then the result ends where string ends. If one multi-column character in string extends across the column width, that character is not included in the result. Thus, the result can fall short of width but cannot go beyond it.
The optional argument start-column specifies the starting column.
If this is non-nil, then the first start-column columns of
the string are omitted from the value. If one multi-column character in
string extends across the column start-column, that
character is not included.
The optional argument padding, if non-nil, is a padding
character added at the beginning and end of the result string, to extend
it to exactly width columns. The padding character is used at the
end of the result if it falls short of width. It is also used at
the beginning of the result if one multi-column character in
string extends across the column start-column.
(truncate-string-to-width "\tab\t" 12 4)
=> "ab"
(truncate-string-to-width "\tab\t" 12 4 ?\ )
=> " ab "
A face is a named collection of graphical attributes: font, foreground color, background color, and optional underlining. Faces control the display of text on the screen.
Each face has its own face number, which distinguishes faces at low levels within Emacs. However, for most purposes, you can refer to faces in Lisp programs by their names.
t if object is a face name symbol (or
if it is a vector of the kind used internally to record face data). It
returns nil otherwise.
Each face name is meaningful for all frames, and by default it has the same meaning in all frames. But you can arrange to give a particular face name a special meaning in one frame if you wish.
This table lists all the standard faces and their uses.
default
modeline
region
secondary-selection
highlight
underline
bold
italic
bold-italic
The way to define a new face is with defface. This creates a
kind of customization item (see section Writing Customization Definitions) which the user can
customize using the Customization buffer (see section `Easy Customization' in The GNU Emacs Manual).
When defface executes, it defines the face according to
spec, then uses any customizations that were read from the
`.emacs' file to override that specification.
The purpose of spec is to specify how the face should appear on
different kinds of terminals. It should be an alist whose elements have
the form (display atts). The element's CAR,
display, specifies a class of terminals. The CDR,
atts, is a list of face attributes and their values; it specifies
what the face should look like on that kind of terminal. The possible
attributes are defined in the value of custom-face-attributes.
The display part of an element of spec determines which frames the element applies to. If more than one element of spec matches a given frame, the first matching element is the only one used for that frame. There are two possibilities for display:
t
t is used in the last (or only) element of spec.
(characteristic value...). Here
characteristic specifies a way of classifying frames, and the
values are possible classifications which display should
apply to. Here are the possible values of characteristic:
type
x, pc
(for the MS-DOS console), w32 (for MS Windows 9X/NT), or
tty.
class
color,
grayscale, or mono.
background
light or dark.
Here's how the standard face region could be defined
with defface:
(defface region
((((class color) (background dark))
(:background "blue"))
(t (:background "gray")))
"Used for displaying the region.")
Internally, defface uses the symbol property
face-defface-spec to record the face attributes specified in
defface, saved-face for the attributes saved by the user
with the customization buffer, and face-documentation for the
documentation string.
nil, specifies the background type to use for
interpreting face definitions. If it is dark, then Emacs treats
all frames as if they had a dark background, regardless of their actual
background colors. If it is light, then Emacs treats all frames
as if they had a light background.
Here are all the ways to specify which face to use for display of text:
face property; if so,
it is displayed with that face. See section Properties with Special Meanings.
If the character has a mouse-face property, that is used instead
of the face property when the mouse is "near enough" to the
character.
face and mouse-face
properties too; they apply to all the text covered by the overlay.
region-face, below).
If these various sources together specify more than one face for a particular character, Emacs merges the attributes of the various faces specified. The attributes of the faces of special glyphs come first; then comes the face for region highlighting, if appropriate; then come attributes of faces from overlays, followed by those from text properties, and last the default face.
When multiple overlays cover one character, an overlay with higher priority overrides those with lower priority. See section Overlays.
If an attribute such as the font or a color is not specified in any of the above ways, the frame's own font or color is used.
The attributes a face can specify include the font, the foreground
color, the background color, and underlining. The face can also leave
these unspecified by giving the value nil for them.
Here are the primitives for creating and changing faces.
nil. It does nothing if there is already a face named
name.
If the optional argument frame is given, this function applies only to that frame. Otherwise it applies to each frame individually, copying attributes from old-face in each frame to new-face in the same frame.
If the optional argument new-frame is given, then copy-face
copies the attributes of old-face in frame to new-name
in new-frame.
You can modify the attributes of an existing face with the following functions. If you specify frame, they affect just that frame; otherwise, they affect all frames as well as the defaults that apply to new frames.
Certain shades of gray are implemented by stipple patterns on black-and-white screens.
nil meaning don't use
stipple.
Normally there is no need to pay attention to stipple patterns, because they are used automatically to handle certain shades of gray.
nil means bold; nil means non-bold.
nil means italic; nil means non-italic.
nil means do underline; nil means don't.
These functions examine the attributes of a face. If you don't specify frame, they refer to the default data for new frames.
nil if it doesn't have one.
nil if none was specified for it.
t if the faces face1 and face2 have the
same attributes for display.
t if the face face displays differently from
the default face. A face is considered to be "the same" as the normal
face if each attribute is either the same as that of the default face or
nil (meaning to inherit from the default).
Normally, the value is the face number of the face named region.
This section describes the mechanism by which Emacs shows a matching open parenthesis when the user inserts a close parenthesis.
blink-paren-function may be nil, in which
case nothing is done.
nil, then blink-matching-open does
nothing.
blink-paren-function. It
assumes that point follows a character with close parenthesis syntax and
moves the cursor momentarily to the matching opening character. If that
character is not already on the screen, it displays the character's
context in the echo area. To avoid long delays, this function does not
search farther than blink-matching-paren-distance characters.
Here is an example of calling this function explicitly.
(defun interactive-blink-matching-open ()
"Indicate momentarily the start of sexp before point."
(interactive)
(let ((blink-matching-paren-distance
(buffer-size))
(blink-matching-paren t))
(blink-matching-open)))
nil means yes, nil means no. The
default is nil.
nil, then mode lines are displayed in inverse video.
Otherwise, mode lines are displayed normally, just like text. The
default is t.
For window frames, this displays mode lines using the face named
modeline, which is normally the inverse of the default face
unless you change it.
The usual display conventions define how to display each character code. You can override these conventions by setting up a display table (see section Display Tables). Here are the usual display conventions:
tab-width.
ctl-arrow. If it is
non-nil, these codes map to sequences of two glyphs, where the
first glyph is the ASCII code for `^'. (A display table can
specify a glyph to use instead of `^'.) Otherwise, these codes map
just like the codes in the range 128 to 255.
The usual display conventions apply even when there is a display
table, for any character whose entry in the active display table is
nil. Thus, when you set up a display table, you need only
specify the characters for which you want special behavior.
These variables affect the way certain characters are displayed on the
screen. Since they change the number of columns the characters occupy,
they also affect the indentation functions. These variables also affect
how the mode line is displayed; if you want to force redisplay of the
mode line using the new values, call the function
force-mode-line-update (see section Mode Line Format).
nil, they are displayed as a caret
followed by the character: `^A'. If it is nil, they are
displayed as a backslash followed by three octal digits: `\001'.
ctl-arrow in
buffers that do not override it. See section The Default Value of a Buffer-Local Variable.
tab-to-tab-stop. See section Adjustable "Tab Stops".
You can use the display table feature to control how all possible character codes display on the screen. This is useful for displaying European languages that have letters not in the ASCII character set.
The display table maps each character code into a sequence of glyphs, each glyph being an image that takes up one character position on the screen. You can also define how to display each glyph on your terminal, using the glyph table.
Display tables affect how the mode line is displayed; if you want to
force redisplay of the mode line using a new display table, call
force-mode-line-update (see section Mode Line Format).
A display table is actually a char-table (see section Char-Tables) with
display-table as its subtype.
nil in all elements.
The ordinary elements of the display table are indexed by character
codes; the element at index c says how to display the character
code c. The value should be nil or a vector of glyph
values (see section Glyphs). If an element is nil, it says to
display that character according to the usual display conventions
(see section Usual Display Conventions).
If you use the display table to change the display of newline characters, the whole buffer will be displayed as one long "line."
The display table also has six "extra slots" which serve special
purposes. Here is a table of their meanings; nil in any slot
means to use the default for that slot, as stated below.
For example, here is how to construct a display table that mimics the
effect of setting ctl-arrow to a non-nil value:
(setq disptab (make-display-table))
(let ((i 0))
(while (< i 32)
(or (= i ?\t) (= i ?\n)
(aset disptab i (vector ?^ (+ i 64))))
(setq i (1+ i)))
(aset disptab 127 (vector ?^ ??)))
truncation, wrap, escape, control,
selective-display, and vertical-border.
truncation, wrap, escape, control,
selective-display, and vertical-border.
Each window can specify a display table, and so can each buffer. When a buffer b is displayed in window w, display uses the display table for window w if it has one; otherwise, the display table for buffer b if it has one; otherwise, the standard display table if any. The display table chosen is called the active display table.
nil
if window does not have an assigned display table.
nil.
nil, that means the buffer does not have an assigned display
table.
nil by default.
If there is no display table to use for a particular window--that is,
if the window specifies none, its buffer specifies none, and
standard-display-table is nil---then Emacs uses the usual
display conventions for all character codes in that window. See section Usual Display Conventions.
A glyph is a generalization of a character; it stands for an image that takes up a single character position on the screen. Glyphs are represented in Lisp as integers, just as characters are.
The meaning of each integer, as a glyph, is defined by the glyph
table, which is the value of the variable glyph-table.
nil instead of a vector, then all glyphs are simple (see
below).
Here are the possible types of elements in the glyph table:
nil
If a glyph code is greater than or equal to the length of the glyph table, that code is automatically simple.
This section describes how to make Emacs ring the bell (or blink the screen) to attract the user's attention. Be conservative about how often you do this; frequent bells can become irritating. Also be careful not to use just beeping when signaling an error is more appropriate. (See section Errors.)
visible-bell below).
It also terminates any keyboard macro currently executing unless
do-not-terminate is non-nil.
ding.
nil means yes, nil means no. This
is effective on a window system, and on a character-only terminal
provided the terminal's Termcap entry defines the visible bell
capability (`vb').
nil, it specifies how Emacs should "ring the
bell." Its value should be a function of no arguments.
Emacs works with several window systems, most notably the X Window System. Both Emacs and X use the term "window", but use it differently. An Emacs frame is a single window as far as X is concerned; the individual Emacs windows are not known to X at all.
x
pc
w32
nil
term-setup-hook.
This hook is used for internal purposes: setting up communication with the window system, and creating the initial window. Users should not interfere with it.
There are many customizations that you can use to make the calendar and diary suit your personal tastes.
If you set the variable view-diary-entries-initially to
t, calling up the calendar automatically displays the diary
entries for the current date as well. The diary dates appear only if
the current date is visible. If you add both of the following lines to
your `.emacs' file:
(setq view-diary-entries-initially t) (calendar)
this displays both the calendar and diary windows whenever you start Emacs.
Similarly, if you set the variable
view-calendar-holidays-initially to t, entering the
calendar automatically displays a list of holidays for the current
three-month period. The holiday list appears in a separate
window.
You can set the variable mark-diary-entries-in-calendar to
t in order to mark any dates with diary entries. This takes
effect whenever the calendar window contents are recomputed. There are
two ways of marking these dates: by changing the face (see section Faces),
if the display supports that, or by placing a plus sign (`+')
beside the date otherwise.
Similarly, setting the variable mark-holidays-in-calendar to
t marks holiday dates, either with a change of face or with an
asterisk (`*').
The variable calendar-holiday-marker specifies how to mark a
date as being a holiday. Its value may be a character to insert next to
the date, or a face name to use for displaying the date. Likewise, the
variable diary-entry-marker specifies how to mark a date that has
diary entries. The calendar creates faces named holiday-face and
diary-face for these purposes; those symbols are the default
values of these variables, when Emacs supports multiple faces on your
terminal.
The variable calendar-load-hook is a normal hook run when the
calendar package is first loaded (before actually starting to display
the calendar).
Starting the calendar runs the normal hook
initial-calendar-window-hook. Recomputation of the calendar
display does not run this hook. But if you leave the calendar with the
q command and reenter it, the hook runs again.
The variable today-visible-calendar-hook is a normal hook run
after the calendar buffer has been prepared with the calendar when the
current date is visible in the window. One use of this hook is to
replace today's date with asterisks; to do that, use the hook function
calendar-star-date.
(add-hook 'today-visible-calendar-hook 'calendar-star-date)
Another standard hook function marks the current date, either by changing its face or by adding an asterisk. Here's how to use it:
(add-hook 'today-visible-calendar-hook 'calendar-mark-today)
The variable calendar-today-marker specifies how to mark today's
date. Its value should be a character to insert next to the date or a
face name to use for displaying the date. A face named
calendar-today-face is provided for this purpose; that symbol is
the default for this variable when Emacs supports multiple faces on your
terminal.
A similar normal hook, today-invisible-calendar-hook is run if
the current date is not visible in the window.
Emacs knows about holidays defined by entries on one of several lists.
You can customize these lists of holidays to your own needs, adding or
deleting holidays. The lists of holidays that Emacs uses are for
general holidays (general-holidays), local holidays
(local-holidays), Christian holidays (christian-holidays),
Hebrew (Jewish) holidays (hebrew-holidays), Islamic (Moslem)
holidays (islamic-holidays), and other holidays
(other-holidays).
The general holidays are, by default, holidays common throughout the
United States. To eliminate these holidays, set general-holidays
to nil.
There are no default local holidays (but sites may supply some). You
can set the variable local-holidays to any list of holidays, as
described below.
By default, Emacs does not include all the holidays of the religions
that it knows, only those commonly found in secular calendars. For a
more extensive collection of religious holidays, you can set any (or
all) of the variables all-christian-calendar-holidays,
all-hebrew-calendar-holidays, or
all-islamic-calendar-holidays to t. If you want to
eliminate the religious holidays, set any or all of the corresponding
variables christian-holidays, hebrew-holidays, and
islamic-holidays to nil.
You can set the variable other-holidays to any list of
holidays. This list, normally empty, is intended for individual use.
Each of the lists (general-holidays, local-holidays,
christian-holidays, hebrew-holidays,
islamic-holidays, and other-holidays) is a list of
holiday forms, each holiday form describing a holiday (or
sometimes a list of holidays).
Here is a table of the possible kinds of holiday form. Day numbers and month numbers count starting from 1, but "dayname" numbers count Sunday as 0. The element string is always the name of the holiday, as a string.
(holiday-fixed month day string)
(holiday-float month dayname k string)
(holiday-hebrew month day string)
(holiday-islamic month day string)
(holiday-julian month day string)
(holiday-sexp sexp string)
year to compute and return the date of a
holiday, or nil if the holiday doesn't happen this year. The
value of sexp must represent the date as a list of the form
(month day year).
(if condition holiday-form)
(function [args])
For example, suppose you want to add Bastille Day, celebrated in France on July 14. You can do this as follows:
(setq other-holidays '((holiday-fixed 7 14 "Bastille Day")))
The holiday form (holiday-fixed 7 14 "Bastille Day") specifies the
fourteenth day of the seventh month (July).
Many holidays occur on a specific day of the week, at a specific time of month. Here is a holiday form describing Hurricane Supplication Day, celebrated in the Virgin Islands on the fourth Monday in August:
(holiday-float 8 1 4 "Hurricane Supplication Day")
Here the 8 specifies August, the 1 specifies Monday (Sunday is 0, Tuesday is 2, and so on), and the 4 specifies the fourth occurrence in the month (1 specifies the first occurrence, 2 the second occurrence, -1 the last occurrence, -2 the second-to-last occurrence, and so on).
You can specify holidays that occur on fixed days of the Hebrew, Islamic, and Julian calendars too. For example,
(setq other-holidays
'((holiday-hebrew 10 2 "Last day of Hanukkah")
(holiday-islamic 3 12 "Mohammed's Birthday")
(holiday-julian 4 2 "Jefferson's Birthday")))
adds the last day of Hanukkah (since the Hebrew months are numbered with 1 starting from Nisan), the Islamic feast celebrating Mohammed's birthday (since the Islamic months are numbered from 1 starting with Muharram), and Thomas Jefferson's birthday, which is 2 April 1743 on the Julian calendar.
To include a holiday conditionally, use either Emacs Lisp's if or the
holiday-sexp form. For example, American presidential elections
occur on the first Tuesday after the first Monday in November of years
divisible by 4:
(holiday-sexp (if (= 0 (% year 4))
(calendar-gregorian-from-absolute
(1+ (calendar-dayname-on-or-before
1 (+ 6 (calendar-absolute-from-gregorian
(list 11 1 year))))))
"US Presidential Election"))
or
(if (= 0 (% displayed-year 4))
(fixed 11
(extract-calendar-day
(calendar-gregorian-from-absolute
(1+ (calendar-dayname-on-or-before
1 (+ 6 (calendar-absolute-from-gregorian
(list 11 1 displayed-year)))))))
"US Presidential Election"))
Some holidays just don't fit into any of these forms because special
calculations are involved in their determination. In such cases you
must write a Lisp function to do the calculation. To include eclipses,
for example, add (eclipses) to other-holidays
and write an Emacs Lisp function eclipses that returns a
(possibly empty) list of the relevant Gregorian dates among the range
visible in the calendar window, with descriptive strings, like this:
(((6 27 1991) "Lunar Eclipse") ((7 11 1991) "Solar Eclipse") ... )
You can customize the manner of displaying dates in the diary, in mode
lines, and in messages by setting calendar-date-display-form.
This variable holds a list of expressions that can involve the variables
month, day, and year, which are all numbers in
string form, and monthname and dayname, which are both
alphabetic strings. In the American style, the default value of this
list is as follows:
((if dayname (concat dayname ", ")) monthname " " day ", " year)
while in the European style this value is the default:
((if dayname (concat dayname ", ")) day " " monthname " " year)
The ISO standard date representation is this:
(year "-" month "-" day)
This specifies a typical American format:
(month "/" day "/" (substring year -2))
The calendar and diary by default display times of day in the
conventional American style with the hours from 1 through 12, minutes,
and either `am' or `pm'. If you prefer the European style,
also known in the US as military, in which the hours go from 00 to 23,
you can alter the variable calendar-time-display-form. This
variable is a list of expressions that can involve the variables
12-hours, 24-hours, and minutes, which are all
numbers in string form, and am-pm and time-zone, which are
both alphabetic strings. The default value of
calendar-time-display-form is as follows:
(12-hours ":" minutes am-pm
(if time-zone " (") time-zone (if time-zone ")"))
Here is a value that provides European style times:
(24-hours ":" minutes
(if time-zone " (") time-zone (if time-zone ")"))
Emacs understands the difference between standard time and daylight savings time--the times given for sunrise, sunset, solstices, equinoxes, and the phases of the moon take that into account. The rules for daylight savings time vary from place to place and have also varied historically from year to year. To do the job properly, Emacs needs to know which rules to use.
Some operating systems keep track of the rules that apply to the place where you are; on these systems, Emacs gets the information it needs from the system automatically. If some or all of this information is missing, Emacs fills in the gaps with the rules currently used in Cambridge, Massachusetts, which is the center of GNU's world.
If the default choice of rules is not appropriate for your location,
you can tell Emacs the rules to use by setting the variables
calendar-daylight-savings-starts and
calendar-daylight-savings-ends. Their values should be Lisp
expressions that refer to the variable year, and evaluate to the
Gregorian date on which daylight savings time starts or (respectively)
ends, in the form of a list (month day year).
The values should be nil if your area does not use daylight
savings time.
Emacs uses these expressions to determine the start and end dates of daylight savings time as holidays and for correcting times of day in the solar and lunar calculations.
The values for Cambridge, Massachusetts are as follows:
(calendar-nth-named-day 1 0 4 year) (calendar-nth-named-day -1 0 10 year)
i.e., the first 0th day (Sunday) of the fourth month (April) in
the year specified by year, and the last Sunday of the tenth month
(October) of that year. If daylight savings time were
changed to start on October 1, you would set
calendar-daylight-savings-starts to this:
(list 10 1 year)
For a more complex example, suppose daylight savings time begins on
the first of Nisan on the Hebrew calendar. You should set
calendar-daylight-savings-starts to this value:
(calendar-gregorian-from-absolute
(calendar-absolute-from-hebrew
(list 1 1 (+ year 3760))))
because Nisan is the first month in the Hebrew calendar and the Hebrew year differs from the Gregorian year by 3760 at Nisan.
If there is no daylight savings time at your location, or if you want
all times in standard time, set calendar-daylight-savings-starts
and calendar-daylight-savings-ends to nil.
The variable calendar-daylight-time-offset specifies the
difference between daylight savings time and standard time, measured in
minutes. The value for Cambridge is 60.
The variable calendar-daylight-savings-starts-time and the
variable calendar-daylight-savings-ends-time specify the number
of minutes after midnight local time when the transition to and from
daylight savings time should occur. For Cambridge, both variables'
values are 120.
Ordinarily, the mode line of the diary buffer window indicates any
holidays that fall on the date of the diary entries. The process of
checking for holidays can take several seconds, so including holiday
information delays the display of the diary buffer noticeably. If you'd
prefer to have a faster display of the diary buffer but without the
holiday information, set the variable holidays-in-diary-buffer to
nil.
The variable number-of-diary-entries controls the number of
days of diary entries to be displayed at one time. It affects the
initial display when view-diary-entries-initially is t, as
well as the command M-x diary. For example, the default value is
1, which says to display only the current day's diary entries. If the
value is 2, both the current day's and the next day's entries are
displayed. The value can also be a vector of seven elements: for
example, if the value is [0 2 2 2 2 4 1] then no diary entries
appear on Sunday, the current date's and the next day's diary entries
appear Monday through Thursday, Friday through Monday's entries appear
on Friday, while on Saturday only that day's entries appear.
The variable print-diary-entries-hook is a normal hook run
after preparation of a temporary buffer containing just the diary
entries currently visible in the diary buffer. (The other, irrelevant
diary entries are really absent from the temporary buffer; in the diary
buffer, they are merely hidden.) The default value of this hook does
the printing with the command lpr-buffer. If you want to use a
different command to do the printing, just change the value of this
hook. Other uses might include, for example, rearranging the lines into
order by day and time.
You can customize the form of dates in your diary file, if neither the
standard American nor European styles suits your needs, by setting the
variable diary-date-forms. This variable is a list of patterns
for recognizing a date. Each date pattern is a list whose elements may
be regular expressions (see section Regular Expressions) or the symbols
month, day, year, monthname, and
dayname. All these elements serve as patterns that match certain
kinds of text in the diary file. In order for the date pattern, as a
whole, to match, all of its elements must match consecutively.
A regular expression in a date pattern matches in its usual fashion, using the standard syntax table altered so that `*' is a word constituent.
The symbols month, day, year, monthname,
and dayname match the month number, day number, year number,
month name, and day name of the date being considered. The symbols that
match numbers allow leading zeros; those that match names allow
three-letter abbreviations and capitalization. All the symbols can
match `*'; since `*' in a diary entry means "any day", "any
month", and so on, it should match regardless of the date being
considered.
The default value of diary-date-forms in the American style is
this:
((month "/" day "[^/0-9]") (month "/" day "/" year "[^0-9]") (monthname " *" day "[^,0-9]") (monthname " *" day ", *" year "[^0-9]") (dayname "\\W"))
The date patterns in the list must be mutually exclusive and
must not match any portion of the diary entry itself, just the date and
one character of whitespace. If, to be mutually exclusive, the pattern
must match a portion of the diary entry text--beyond the whitespace
that ends the date--then the first element of the date pattern
must be backup. This causes the date recognizer to back
up to the beginning of the current word of the diary entry, after
finishing the match. Even if you use backup, the date pattern
must absolutely not match more than a portion of the first word of the
diary entry. The default value of diary-date-forms in the
European style is this list:
((day "/" month "[^/0-9]") (day "/" month "/" year "[^0-9]") (backup day " *" monthname "\\W+\\<[^*0-9]") (day " *" monthname " *" year "[^0-9]") (dayname "\\W"))
Notice the use of backup in the third pattern, because it needs
to match part of a word beyond the date itself to distinguish it from
the fourth pattern.
Your diary file can have entries based on Hebrew or Islamic dates, as well as entries based on the world-standard Gregorian calendar. However, because recognition of such entries is time-consuming and most people don't use them, you must explicitly enable their use. If you want the diary to recognize Hebrew-date diary entries, for example, you must do this:
(add-hook 'nongregorian-diary-listing-hook 'list-hebrew-diary-entries) (add-hook 'nongregorian-diary-marking-hook 'mark-hebrew-diary-entries)
If you want Islamic-date entries, do this:
(add-hook 'nongregorian-diary-listing-hook 'list-islamic-diary-entries) (add-hook 'nongregorian-diary-marking-hook 'mark-islamic-diary-entries)
Hebrew- and Islamic-date diary entries have the same formats as Gregorian-date diary entries, except that `H' precedes a Hebrew date and `I' precedes an Islamic date. Moreover, because the Hebrew and Islamic month names are not uniquely specified by the first three letters, you may not abbreviate them. For example, a diary entry for the Hebrew date Heshvan 25 could look like this:
HHeshvan 25 Happy Hebrew birthday!
and would appear in the diary for any date that corresponds to Heshvan 25 on the Hebrew calendar. And here is an Islamic-date diary entry that matches Dhu al-Qada 25:
IDhu al-Qada 25 Happy Islamic birthday!
As with Gregorian-date diary entries, Hebrew- and Islamic-date entries are nonmarking if they are preceded with an ampersand (`&').
Here is a table of commands used in the calendar to create diary entries that match the selected date and other dates that are similar in the Hebrew or Islamic calendar:
insert-hebrew-diary-entry).
insert-monthly-hebrew-diary-entry). This diary
entry matches any date that has the same Hebrew day-within-month as the
selected date.
insert-yearly-hebrew-diary-entry). This diary
entry matches any date which has the same Hebrew month and day-within-month
as the selected date.
insert-islamic-diary-entry).
insert-monthly-islamic-diary-entry).
insert-yearly-islamic-diary-entry).
These commands work much like the corresponding commands for ordinary diary entries: they apply to the date that point is on in the calendar window, and what they do is insert just the date portion of a diary entry at the end of your diary file. You must then insert the rest of the diary entry.
Diary display works by preparing the diary buffer and then running the
hook diary-display-hook. The default value of this hook
(simple-diary-display) hides the irrelevant diary entries and
then displays the buffer. However, if you specify the hook as follows,
(add-hook 'diary-display-hook 'fancy-diary-display)
this enables fancy diary display. It displays diary entries and holidays by copying them into a special buffer that exists only for the sake of display. Copying to a separate buffer provides an opportunity to change the displayed text to make it prettier--for example, to sort the entries by the dates they apply to.
As with simple diary display, you can print a hard copy of the buffer
with print-diary-entries. To print a hard copy of a day-by-day
diary for a week by positioning point on Sunday of that week, type
7 d and then do M-x print-diary-entries. As usual, the
inclusion of the holidays slows down the display slightly; you can speed
things up by setting the variable holidays-in-diary-buffer to
nil.
Ordinarily, the fancy diary buffer does not show days for which there are
no diary entries, even if that day is a holiday. If you want such days to be
shown in the fancy diary buffer, set the variable
diary-list-include-blanks to t.
If you use the fancy diary display, you can use the normal hook
list-diary-entries-hook to sort each day's diary entries by their
time of day. Here's how:
(add-hook 'list-diary-entries-hook 'sort-diary-entries t)
For each day, this sorts diary entries that begin with a recognizable time of day according to their times. Diary entries without times come first within each day.
Fancy diary display also has the ability to process included diary files. This permits a group of people to share a diary file for events that apply to all of them. Lines in the diary file of this form:
#include "filename"
includes the diary entries from the file filename in the fancy diary buffer. The include mechanism is recursive, so that included files can include other files, and so on; you must be careful not to have a cycle of inclusions, of course. Here is how to enable the include facility:
(add-hook 'list-diary-entries-hook 'include-other-diary-files) (add-hook 'mark-diary-entries-hook 'mark-included-diary-files)
The include mechanism works only with the fancy diary display, because ordinary diary display shows the entries directly from your diary file.
Sexp diary entries allow you to do more than just have complicated conditions under which a diary entry applies. If you use the fancy diary display, sexp entries can generate the text of the entry depending on the date itself. For example, an anniversary diary entry can insert the number of years since the anniversary date into the text of the diary entry. Thus the `%d' in this dairy entry:
%%(diary-anniversary 10 31 1948) Arthur's birthday (%d years old)
gets replaced by the age, so on October 31, 1990 the entry appears in the fancy diary buffer like this:
Arthur's birthday (42 years old)
If the diary file instead contains this entry:
%%(diary-anniversary 10 31 1948) Arthur's %d%s birthday
the entry in the fancy diary buffer for October 31, 1990 appears like this:
Arthur's 42nd birthday
Similarly, cyclic diary entries can interpolate the number of repetitions that have occurred:
%%(diary-cyclic 50 1 1 1990) Renew medication (%d%s time)
looks like this:
Renew medication (5th time)
in the fancy diary display on September 8, 1990.
There is an early reminder diary sexp that includes its entry in the diary not only on the date of occurrence, but also on earlier dates. For example, if you want a reminder a week before your anniversary, you can use
%%(diary-remind '(diary-anniversary 12 22 1968) 7) Ed's anniversary
and the fancy diary will show
Ruth & Ed's anniversary
both on December 15 and on December 22.
The function diary-date applies to dates described by a month,
day, year combination, each of which can be an integer, a list of
integers, or t. The value t means all values. For
example,
%%(diary-date '(10 11 12) 22 t) Rake leaves
causes the fancy diary to show
Rake leaves
on October 22, November 22, and December 22 of every year.
The function diary-float allows you to describe diary entries
that apply to dates like the third Friday of November, or the last
Tuesday in April. The parameters are the month, dayname,
and an index n. The entry appears on the nth dayname
of month, where dayname=0 means Sunday, 1 means Monday, and
so on. If n is negative it counts backward from the end of
month. The value of month can be a list of months, a single
month, or t to specify all months. You can also use an optional
parameter day to specify the nth dayname of
month on or after/before day; the value of day defaults
to 1 if n is positive and to the last day of month if
n is negative. For example,
%%(diary-float t 1 -1) Pay rent
causes the fancy diary to show
Pay rent
on the last Monday of every month.
The generality of sexp diary entries lets you specify any diary entry
that you can describe algorithmically. A sexp diary entry contains an
expression that computes whether the entry applies to any given date.
If its value is non-nil, the entry applies to that date;
otherwise, it does not. The expression can use the variable date
to find the date being considered; its value is a list (month
day year) that refers to the Gregorian calendar.
Suppose you get paid on the 21st of the month if it is a weekday, and on the Friday before if the 21st is on a weekend. Here is how to write a sexp diary entry that matches those dates:
&%%(let ((dayname (calendar-day-of-week date))
(day (car (cdr date))))
(or (and (= day 21) (memq dayname '(1 2 3 4 5)))
(and (memq day '(19 20)) (= dayname 5)))
) Pay check deposited
The following sexp diary entries take advantage of the ability (in the fancy diary display) to concoct diary entries whose text varies based on the date:
%%(diary-sunrise-sunset)
%%(diary-phases-of-moon)
%%(diary-day-of-year)
%%(diary-iso-date)
%%(diary-julian-date)
%%(diary-astro-day-number)
%%(diary-hebrew-date)
%%(diary-islamic-date)
%%(diary-french-date)
%%(diary-mayan-date)
Thus including the diary entry
&%%(diary-hebrew-date)
causes every day's diary display to contain the equivalent date on the Hebrew calendar, if you are using the fancy diary display. (With simple diary display, the line `&%%(diary-hebrew-date)' appears in the diary for any date, but does nothing particularly useful.)
These functions can be used to construct sexp diary entries based on the Hebrew calendar in certain standard ways:
%%(diary-rosh-hodesh)
%%(diary-parasha)
%%(diary-sabbath-candles)
%%(diary-omer)
%%(diary-yahrzeit month day year) name
You can specify exactly how Emacs reminds you of an appointment, and how far in advance it begins doing so, by setting these variables:
appt-message-warning-time
appt-audible
nil, Emacs rings the
terminal bell for appointment reminders. The default is t.
appt-visible
nil, Emacs displays the appointment
message in the echo area. The default is t.
appt-display-mode-line
nil, Emacs displays the number of minutes
to the appointment on the mode line. The default is t.
appt-msg-window
nil, Emacs displays the appointment
message in another window. The default is t.
appt-disp-window-function
appt-delete-window-function
appt-display-duration
This chapter describes no additional features of Emacs Lisp. Instead it gives advice on making effective use of the features described in the previous chapters, and describes conventions Emacs Lisp programmers should follow.
Here are conventions that you should follow when writing Emacs Lisp code intended for widespread use:
copy-list. Believe it or not, there is more than one plausible
way to define copy-list. Play it safe; append your name prefix
to produce a name like foo-copy-list or mylib-copy-list
instead.
If you write a function that you think ought to be added to Emacs under
a certain name, such as twiddle-files, don't call it by that name
in your program. Call it mylib-twiddle-files in your program,
and send mail to `bug-gnu-emacs@gnu.org' suggesting we add
it to Emacs. If and when we do, we can change the name easily enough.
If one prefix is insufficient, your package may use two or three
alternative common prefixes, so long as they make sense.
Separate the prefix from the rest of the symbol name with a hyphen,
`-'. This will be consistent with Emacs itself and with most Emacs
Lisp programs.
provide in each separate
library program, at least if there is more than one entry point to the
program.
require to make sure they are loaded.
(eval-when-compile (require 'bar))(And the library bar should contain
(provide 'bar),
to make the require work.) This will cause bar to be
loaded when you byte-compile foo. Otherwise, you risk compiling
foo without the necessary macro loaded, and that would produce
compiled code that won't work right. See section Macros and Byte Compilation.
Using eval-when-compile avoids loading bar when
the compiled version of foo is used.
framep and frame-live-p.
whatever-mode which turns the feature on or
off, and make it autoload (see section Autoload). Design the package so
that simply loading it has no visible effect--that should not enable
the feature. Users will request the feature by invoking the command.
next-line or previous-line in programs; nearly
always, forward-line is more convenient as well as more
predictable and robust. See section Motion by Text Lines.
beginning-of-buffer, end-of-buffer
replace-string, replace-regexp
message function, not princ. See section The Echo Area.
error
(or signal). The function error does not return.
See section How to Signal an Error.
Do not use message, throw, sleep-for,
or beep to report errors.
edit-options command does: switch to another buffer and let the
user switch back at will. See section Recursive Editing.
defvar definitions for these variables.
If you bind a variable in one function, and use it or set it in another
function, the compiler warns about the latter function unless the
variable has a definition. But often these variables have short names,
and it is not clean for Lisp packages to define such variable names.
Therefore, you should rename the variable to start with the name prefix
used for the other functions and variables in your package.
indent-sexp) using the
default indentation parameters.
;; Copyright (C) year name ;; This program is free software; you can redistribute it and/or ;; modify it under the terms of the GNU General Public License as ;; published by the Free Software Foundation; either version 2 of ;; the License, or (at your option) any later version. ;; This program is distributed in the hope that it will be ;; useful, but WITHOUT ANY WARRANTY; without even the implied ;; warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR ;; PURPOSE. See the GNU General Public License for more details. ;; You should have received a copy of the GNU General Public ;; License along with this program; if not, write to the Free ;; Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, ;; MA 02111-1307 USAIf you have signed papers to assign the copyright to the Foundation, then use `Free Software Foundation, Inc.' as name. Otherwise, use your name.
Here are ways of improving the execution speed of byte-compiled Lisp programs.
memq, member,
assq, or assoc is even faster than explicit iteration. It
can be worth rearranging a data structure so that one of these primitive
search functions can be used.
byte-compile
property. If the property is non-nil, then the function is
handled specially.
For example, the following input will show you that aref is
compiled specially (see section Functions that Operate on Arrays):
(get 'aref 'byte-compile)
=> byte-compile-two-args
Here are some tips and conventions for the writing of documentation strings. You can check many of these conventions by running the command M-x checkdoc-minor-mode.
nil values are equivalent and indicate explicitly what
nil and non-nil mean.
/ refers to its second argument as `DIVISOR', because the
actual argument name is divisor.
Also use all caps for meta-syntactic variables, such as when you show
the decomposition of a list or vector into subunits, some of which may
vary.
t and nil without single-quotes.
Help mode automatically creates a hyperlink when a documentation string
uses a symbol name inside single quotes, if the symbol has either a
function or a variable definition. You do not need to do anything
special to make use of this feature. However, when a symbol has both a
function definition and a variable definition, and you want to refer to
just one of them, you can specify which one by writing one of the words
`variable', `option', `function', or `command',
immediately before the symbol name. (Case makes no difference in
recognizing these indicator words.) For example, if you write
This function sets the variable `buffer-file-name'.then the hyperlink will refer only to the variable documentation of
buffer-file-name, and not to its function documentation.
If a symbol has a function definition and/or a variable definition, but
those are irrelevant to the use of the symbol that you are documenting,
you can write the word `symbol' before the symbol name to prevent
making any hyperlink. For example,
If the argument KIND-OF-RESULT is the symbol `list', this function returns a list of all the objects that satisfy the criterion.does not make a hyperlink to the documentation, irrelevant here, of the function
list.
forward-char.
(This is normally `C-f', but it may be some other character if the
user has moved key bindings.) See section Substituting Key Bindings in Documentation.
We recommend these conventions for where to put comments and how to indent them:
indent-for-comment)
command automatically inserts such a `;' in the right place, or
aligns such a comment if it is already present.
This and following examples are taken from the Emacs sources.
(setq base-version-list ; there was a base
(assoc (substring fn 0 start-vn) ; version to which
file-version-assoc-list)) ; this looks like
; a subversion
(prog1 (setq auto-fill-function
...
...
;; update mode line
(force-mode-line-update)))
Every function that has no documentation string (presumably one that is
used only internally within the package it belongs to), should have
instead a two-semicolon comment right before the function, explaining
what the function does and how to call it properly. Explain precisely
what each argument means and how the function interprets its possible
values.
;;; This Lisp code is run in Emacs ;;; when it is to operate as a server ;;; for other processes.Another use for triple-semicolon comments is for commenting out lines within a function. We use triple-semicolons for this precisely so that they remain at the left margin.
(defun foo (a) ;;; This is no longer necessary. ;;; (force-mode-line-update) (message "Finished with %s" a))
;;;; The kill ring
The indentation commands of the Lisp modes in Emacs, such as M-;
(indent-for-comment) and TAB (lisp-indent-line),
automatically indent comments according to these conventions,
depending on the number of semicolons. See section `Manipulating Comments' in The GNU Emacs Manual.
Emacs has conventions for using special comments in Lisp libraries to divide them into sections and give information such as who wrote them. This section explains these conventions. First, an example:
;;; lisp-mnt.el --- minor mode for Emacs Lisp maintainers ;; Copyright (C) 1992 Free Software Foundation, Inc. ;; Author: Eric S. Raymond <esr@snark.thyrsus.com> ;; Maintainer: Eric S. Raymond <esr@snark.thyrsus.com> ;; Created: 14 Jul 1992 ;; Version: 1.2 ;; Keywords: docs ;; This file is part of GNU Emacs. ... ;; Free Software Foundation, Inc., 59 Temple Place - Suite 330, ;; Boston, MA 02111-1307, USA.
The very first line should have this format:
;;; filename --- description
The description should be complete in one line.
After the copyright notice come several header comment lines, each beginning with `;; header-name:'. Here is a table of the conventional possibilities for header-name:
;; and a tab character, like this:
;; Author: Ashwin Ram <Ram-Ashwin@cs.yale.edu> ;; Dave Sill <de5@ornl.gov> ;; Dave Brennan <brennan@hal.com> ;; Eric Raymond <esr@snark.thyrsus.com>
finder-by-keyword help command.
Please use that command to see a list of the meaningful keywords.
This field is important; it's how people will find your package when
they're looking for things by topic area. To separate the keywords, you
can use spaces, commas, or both.
Just about every Lisp library ought to have the `Author' and `Keywords' header comment lines. Use the others if they are appropriate. You can also put in header lines with other header names--they have no standard meanings, so they can't do any harm.
We use additional stylized comments to subdivide the contents of the library file. Here is a table of them:
This chapter describes how the runnable Emacs executable is dumped with the preloaded Lisp libraries in it, how storage is allocated, and some internal aspects of GNU Emacs that may be of interest to C programmers.
This section explains the steps involved in building the Emacs executable. You don't have to know this material to build and install Emacs, since the makefiles do all these things automatically. This information is pertinent to Emacs maintenance.
Compilation of the C source files in the `src' directory produces an executable file called `temacs', also called a bare impure Emacs. It contains the Emacs Lisp interpreter and I/O routines, but not the editing commands.
The command `temacs -l loadup' uses `temacs' to create the real runnable Emacs executable. These arguments direct `temacs' to evaluate the Lisp files specified in the file `loadup.el'. These files set up the normal Emacs editing environment, resulting in an Emacs that is still impure but no longer bare.
It takes a substantial time to load the standard Lisp files. Luckily, you don't have to do this each time you run Emacs; `temacs' can dump out an executable program called `emacs' that has these files preloaded. `emacs' starts more quickly because it does not need to load the files. This is the Emacs executable that is normally installed.
To create `emacs', use the command `temacs -batch -l loadup dump'. The purpose of `-batch' here is to prevent `temacs' from trying to initialize any of its data on the terminal; this ensures that the tables of terminal information are empty in the dumped Emacs. The argument `dump' tells `loadup.el' to dump a new executable named `emacs'.
Some operating systems don't support dumping. On those systems, you must start Emacs with the `temacs -l loadup' command each time you use it. This takes a substantial time, but since you need to start Emacs once a day at most--or once a week if you never log out--the extra time is not too severe a problem.
You can specify additional files to preload by writing a library named
`site-load.el' that loads them. You may need to increase the value
of PURESIZE, in `src/puresize.h', to make room for the
additional data. (Try adding increments of 20000 until it is big
enough.) However, the advantage of preloading additional files
decreases as machines get faster. On modern machines, it is usually not
advisable.
After `loadup.el' reads `site-load.el', it finds the
documentation strings for primitive and preloaded functions (and
variables) in the file `etc/DOC' where they are stored, by calling
Snarf-documentation (see section Access to Documentation Strings).
You can specify other Lisp expressions to execute just before dumping by putting them in a library named `site-init.el'. This file is executed after the documentation strings are found.
If you want to preload function or variable definitions, there are three ways you can do this and make their documentation strings accessible when you subsequently run Emacs:
nil value for
byte-compile-dynamic-docstrings as a local variable in each these
files, and load them with either `site-load.el' or
`site-init.el'. (This method has the drawback that the
documentation strings take up space in Emacs all the time.)
It is not advisable to put anything in `site-load.el' or `site-init.el' that would alter any of the features that users expect in an ordinary unmodified Emacs. If you feel you must override normal features for your site, do it with `default.el', so that users can override your changes if they wish. See section Summary: Sequence of Actions at Start Up.
If you want to use this function in an Emacs that was already dumped, you must run Emacs with `-batch'.
Emacs Lisp uses two kinds of storage for user-created Lisp objects: normal storage and pure storage. Normal storage is where all the new data created during an Emacs session is kept; see the following section for information on normal storage. Pure storage is used for certain data in the preloaded standard Lisp files--data that should never change during actual use of Emacs.
Pure storage is allocated only while `temacs' is loading the
standard preloaded Lisp libraries. In the file `emacs', it is
marked as read-only (on operating systems that permit this), so that
the memory space can be shared by all the Emacs jobs running on the
machine at once. Pure storage is not expandable; a fixed amount is
allocated when Emacs is compiled, and if that is not sufficient for the
preloaded libraries, `temacs' crashes. If that happens, you must
increase the compilation parameter PURESIZE in the file
`src/puresize.h'. This normally won't happen unless you try to
preload additional libraries or add features to the standard ones.
This function is a no-op except while Emacs is being built and dumped; it is usually called only in the file `emacs/lisp/loaddefs.el', but a few packages call it just in case you decide to preload them.
defun should make a copy of the
function definition in pure storage. If it is non-nil, then the
function definition is copied into pure storage.
This flag is t while loading all of the basic functions for
building Emacs initially (allowing those functions to be sharable and
non-collectible). Dumping Emacs as an executable always writes
nil in this variable, regardless of the value it actually has
before and after dumping.
You should not change this flag in a running Emacs.
When a program creates a list or the user defines a new function (such as by loading a library), that data is placed in normal storage. If normal storage runs low, then Emacs asks the operating system to allocate more memory in blocks of 1k bytes. Each block is used for one type of Lisp object, so symbols, cons cells, markers, etc., are segregated in distinct blocks in memory. (Vectors, long strings, buffers and certain other editing types, which are fairly large, are allocated in individual blocks, one per object, while small strings are packed into blocks of 8k bytes.)
It is quite common to use some storage for a while, then release it by (for example) killing a buffer or deleting the last pointer to an object. Emacs provides a garbage collector to reclaim this abandoned storage. (This name is traditional, but "garbage recycler" might be a more intuitive metaphor for this facility.)
The garbage collector operates by finding and marking all Lisp objects that are still accessible to Lisp programs. To begin with, it assumes all the symbols, their values and associated function definitions, and any data presently on the stack, are accessible. Any objects that can be reached indirectly through other accessible objects are also accessible.
When marking is finished, all objects still unmarked are garbage. No matter what the Lisp program or the user does, it is impossible to refer to them, since there is no longer a way to reach them. Their space might as well be reused, since no one will miss them. The second ("sweep") phase of the garbage collector arranges to reuse them.
The sweep phase puts unused cons cells onto a free list
for future allocation; likewise for symbols and markers. It compacts
the accessible strings so they occupy fewer 8k blocks; then it frees the
other 8k blocks. Vectors, buffers, windows, and other large objects are
individually allocated and freed using malloc and free.
Common Lisp note: Unlike other Lisps, GNU Emacs Lisp does not call the garbage collector when the free list is empty. Instead, it simply requests the operating system to allocate more storage, and processing continues until
gc-cons-thresholdbytes have been used.This means that you can make sure that the garbage collector will not run during a certain portion of a Lisp program by calling the garbage collector explicitly just before it (provided that portion of the program does not use so much space as to force a second garbage collection).
gc-cons-threshold bytes of
Lisp data since the previous garbage collection.)
garbage-collect returns a list containing the following
information:
((used-conses . free-conses) (used-syms . free-syms) (used-miscs . free-miscs) used-string-chars used-vector-slots (used-floats . free-floats) (used-intervals . free-intervals))
Here is an example:
(garbage-collect)
=> ((106886 . 13184) (9769 . 0)
(7731 . 4651) 347543 121628
(31 . 94) (1273 . 168))
Here is a table explaining each element:
nil, Emacs displays a message at the
beginning and end of garbage collection. The default value is
nil, meaning there are no such messages.
The initial threshold value is 400,000. If you specify a larger value, garbage collection will happen less often. This reduces the amount of time spent garbage collecting, but increases total memory use. You may want to do this when running a program that creates lots of Lisp data.
You can make collections more frequent by specifying a smaller value,
down to 10,000. A value less than 10,000 will remain in effect only
until the subsequent garbage collection, at which time
garbage-collect will set the threshold back to 10,000.
The value return by garbage-collect describes the amount of
memory used by Lisp data, broken down by data type. By contrast, the
function memory-limit provides information on the total amount of
memory Emacs is currently using.
You can use this to get a general idea of how your actions affect the memory usage.
These functions and variables give information about the total amount
of memory allocation that Emacs has done, broken down by data type.
Note the difference between these and the values returned by
(garbage-collect); those count objects that currently exist, but
these count the number or size of all allocations, including those for
objects that have since been freed.
Lisp primitives are Lisp functions implemented in C. The details of interfacing the C function so that Lisp can call it are handled by a few C macros. The only way to really understand how to write new C code is to read the source, but we can explain some things here.
An example of a special form is the definition of or, from
`eval.c'. (An ordinary function would have the same general
appearance.)
DEFUN ("or", For, Sor, 0, UNEVALLED, 0,
"Eval args until one of them yields non-nil; return that value.\n\
The remaining args are not evalled at all.\n\
If all args return nil, return nil.")
(args)
Lisp_Object args;
{
register Lisp_Object val;
Lisp_Object args_left;
struct gcpro gcpro1;
if (NULL (args))
return Qnil;
args_left = args;
GCPRO1 (args_left);
do
{
val = Feval (Fcar (args_left));
if (!NULL (val))
break;
args_left = Fcdr (args_left);
}
while (!NULL (args_left));
UNGCPRO;
return val;
}
Let's start with a precise explanation of the arguments to the
DEFUN macro. Here is a template for them:
DEFUN (lname, fname, sname, min, max, interactive, doc)
or.
For. Remember that the arguments must
be of type Lisp_Object; various macros and functions for creating
values of type Lisp_Object are declared in the file
`lisp.h'.
or allows a minimum of zero arguments.
UNEVALLED,
indicating a special form that receives unevaluated arguments, or
MANY, indicating an unlimited number of evaluated arguments (the
equivalent of &rest). Both UNEVALLED and MANY are
macros. If max is a number, it may not be less than min and
it may not be greater than seven.
interactive in a Lisp function. In the case of
or, it is 0 (a null pointer), indicating that or cannot be
called interactively. A value of "" indicates a function that
should receive no arguments when called interactively.
After the call to the DEFUN macro, you must write the argument
name list that every C function must have, followed by ordinary C
declarations for the arguments. For a function with a fixed maximum
number of arguments, declare a C argument for each Lisp argument, and
give them all type Lisp_Object. When a Lisp function has no
upper limit on the number of arguments, its implementation in C actually
receives exactly two arguments: the first is the number of Lisp
arguments, and the second is the address of a block containing their
values. They have types int and Lisp_Object *.
Within the function For itself, note the use of the macros
GCPRO1 and UNGCPRO. GCPRO1 is used to "protect"
a variable from garbage collection--to inform the garbage collector that
it must look in that variable and regard its contents as an accessible
object. This is necessary whenever you call Feval or anything
that can directly or indirectly call Feval. At such a time, any
Lisp object that you intend to refer to again must be protected somehow.
UNGCPRO cancels the protection of the variables that are
protected in the current function. It is necessary to do this explicitly.
For most data types, it suffices to protect at least one pointer to the object; as long as the object is not recycled, all pointers to it remain valid. This is not so for strings, because the garbage collector can move them. When the garbage collector moves a string, it relocates all the pointers it knows about; any other pointers become invalid. Therefore, you must protect all pointers to strings across any point where garbage collection may be possible.
The macro GCPRO1 protects just one local variable. If you want
to protect two, use GCPRO2 instead; repeating GCPRO1 will
not work. Macros GCPRO3 and GCPRO4 also exist.
These macros implicitly use local variables such as gcpro1; you
must declare these explicitly, with type struct gcpro. Thus, if
you use GCPRO2, you must declare gcpro1 and gcpro2.
Alas, we can't explain all the tricky details here.
You must not use C initializers for static or global variables unless they are never written once Emacs is dumped. These variables with initializers are allocated in an area of memory that becomes read-only (on certain operating systems) as a result of dumping Emacs. See section Pure Storage.
Do not use static variables within functions--place all static
variables at top level in the file. This is necessary because Emacs on
some operating systems defines the keyword static as a null
macro. (This definition is used because those systems put all variables
declared static in a place that becomes read-only after dumping, whether
they have initializers or not.)
Defining the C function is not enough to make a Lisp primitive available; you must also create the Lisp symbol for the primitive and store a suitable subr object in its function cell. The code looks like this:
defsubr (&subr-structure-name);
Here subr-structure-name is the name you used as the third
argument to DEFUN.
If you add a new primitive to a file that already has Lisp primitives
defined in it, find the function (near the end of the file) named
syms_of_something, and add the call to defsubr
there. If the file doesn't have this function, or if you create a new
file, add to it a syms_of_filename (e.g.,
syms_of_myfile). Then find the spot in `emacs.c' where all
of these functions are called, and add a call to
syms_of_filename there.
The function syms_of_filename is also the place to define
any C variables that are to be visible as Lisp variables.
DEFVAR_LISP makes a C variable of type Lisp_Object visible
in Lisp. DEFVAR_INT makes a C variable of type int
visible in Lisp with a value that is always an integer.
DEFVAR_BOOL makes a C variable of type int visible in Lisp
with a value that is either t or nil.
If you define a file-scope C variable of type Lisp_Object,
you must protect it for garbage-collection by calling staticpro
in syms_of_filename, like this:
staticpro (&variable);
Here is another example function, with more complicated arguments. This comes from the code in `window.c', and it demonstrates the use of macros and functions to manipulate Lisp objects.
DEFUN ("coordinates-in-window-p", Fcoordinates_in_window_p,
Scoordinates_in_window_p, 2, 2,
"xSpecify coordinate pair: \nXExpression which evals to window: ",
"Return non-nil if COORDINATES is in WINDOW.\n\
COORDINATES is a cons of the form (X . Y), X and Y being distances\n\
...
If they are on the border between WINDOW and its right sibling,\n\
`vertical-line' is returned.")
(coordinates, window)
register Lisp_Object coordinates, window;
{
int x, y;
CHECK_LIVE_WINDOW (window, 0);
CHECK_CONS (coordinates, 1);
x = XINT (Fcar (coordinates));
y = XINT (Fcdr (coordinates));
switch (coordinates_in_window (XWINDOW (window), &x, &y))
{
case 0: /* NOT in window at all. */
return Qnil;
case 1: /* In text part of window. */
return Fcons (make_number (x), make_number (y));
case 2: /* In mode line of window. */
return Qmode_line;
case 3: /* On right border of window. */
return Qvertical_line;
default:
abort ();
}
}
Note that C code cannot call functions by name unless they are defined
in C. The way to call a function written in Lisp is to use
Ffuncall, which embodies the Lisp function funcall. Since
the Lisp function funcall accepts an unlimited number of
arguments, in C it takes two: the number of Lisp-level arguments, and a
one-dimensional array containing their values. The first Lisp-level
argument is the Lisp function to call, and the rest are the arguments to
pass to it. Since Ffuncall can call the evaluator, you must
protect pointers from garbage collection around the call to
Ffuncall.
The C functions call0, call1, call2, and so on,
provide handy ways to call a Lisp function conveniently with a fixed
number of arguments. They work by calling Ffuncall.
`eval.c' is a very good file to look through for examples; `lisp.h' contains the definitions for some important macros and functions.
GNU Emacs Lisp manipulates many different types of data. The actual data are stored in a heap and the only access that programs have to it is through pointers. Pointers are thirty-two bits wide in most implementations. Depending on the operating system and type of machine for which you compile Emacs, twenty-eight bits are used to address the object, and the remaining four bits are used for a GC mark bit and the tag that identifies the object's type.
Because Lisp objects are represented as tagged pointers, it is always
possible to determine the Lisp data type of any object. The C data type
Lisp_Object can hold any Lisp object of any data type. Ordinary
variables have type Lisp_Object, which means they can hold any
type of Lisp value; you can determine the actual data type only at run
time. The same is true for function arguments; if you want a function
to accept only a certain type of argument, you must check the type
explicitly using a suitable predicate (see section Type Predicates).
Buffers contain fields not directly accessible by the Lisp programmer. We describe them here, naming them by the names used in the C code. Many are accessible indirectly in Lisp programs via Lisp primitives.
name
save_modified
modtime
auto_save_modified
last_window_start
window-start position in the buffer as of
the last time the buffer was displayed in a window.
undo_list
syntax_table_v
downcase_table
upcase_table
case_canon_table
case_eqv_table
display_table
nil if it doesn't
have one. See section Display Tables.
markers
backed_up
mark
markers. See section The Mark.
mark_active
nil if the buffer's mark is active.
local_var_alist
base_buffer
nil.
keymap
overlay_center
overlays_before
overlays_after
enable_multibyte_characters
enable-multibyte-characters---either t or nil.
Windows have the following accessible fields:
frame
mini_p
nil if this window is a minibuffer window.
buffer
dedicated
nil if this window is dedicated to its buffer.
pointm
start
force_start
nil, it says that the window has been
scrolled explicitly by the Lisp program. This affects what the next
redisplay does if point is off the screen: instead of scrolling the
window to show the text around point, it moves point to a location that
is on the screen.
last_modified
modified field of the window's buffer, as of the last time
a redisplay completed in this window.
last_point
left
top
height
width
next
nil in a window that is the rightmost or bottommost of a group of
siblings.
prev
nil in a window that is the leftmost or topmost of a group of
siblings.
parent
hscroll
use_time
get-lru-window uses this field.
display_table
nil if none is specified for it.
update_mode_line
nil means this window's mode line needs to be updated.
base_line_number
nil.
This is used for displaying the line number of point in the mode line.
base_line_pos
nil meaning none is known.
region_showing
nil.
The fields of a process are:
name
command
filter
nil.
sentinel
nil.
buffer
pid
childp
nil if this is really a child process.
It is nil for a network connection.
mark
kill_without_query
nil, killing Emacs while this process is still
running does not ask for confirmation about killing the process.
raw_status_low
raw_status_high
wait system call.
status
process-status should return it.
tick
update_tick
pty_flag
nil if communication with the subprocess uses a PTY;
nil if it uses a pipe.
infd
outfd
subtty
nil.)
tty_name
nil if it is using pipes.
Here is the complete list of the error symbols in standard Emacs,
grouped by concept. The list includes each symbol's message (on the
error-message property of the symbol) and a cross reference to a
description of how the error can occur.
Each error symbol has an error-conditions property that is a
list of symbols. Normally this list includes the error symbol itself
and the symbol error. Occasionally it includes additional
symbols, which are intermediate classifications, narrower than
error but broader than a single error symbol. For example, all
the errors in accessing files have the condition file-error. If
we do not say here that a certain error symbol has additional error
conditions, that means it has none.
As a special exception, the error symbol quit does not have the
condition error, because quitting is not considered an error.
See section Errors, for an explanation of how errors are generated and handled.
symbol
error
"error"quit
"Quit"args-out-of-range
"Args out of range"arith-error
"Arithmetic error"/ and % in section Numbers.
beginning-of-buffer
"Beginning of buffer"buffer-read-only
"Buffer is read-only"cyclic-function-indirection
"Symbol's chain of function indirections\
contains a loop"end-of-buffer
"End of buffer"end-of-file
"End of file during parsing"file-error
because it pertains to the Lisp reader, not to file I/O.
See section Input Functions.
file-already-exists
file-error.file-date-error
file-error. It occurs when
copy-file tries and fails to set the last-modification time of
the output file. See section Changing File Names and Attributes.
file-error
file-error is present.file-locked
file-error.file-supersession
file-error.invalid-function
"Invalid function"invalid-read-syntax
"Invalid read syntax"invalid-regexp
"Invalid regexp"mark-inactive
"Mark inactive"no-catch
"No catch for tag"catch and throw.
scan-error
"Scan error"search-failed
"Search failed"setting-constant
"Attempt to set a constant symbol"nil and t,
and any symbols that start with `:',
may not be changed.undefined-color
"Undefined color"void-function
"Symbol's function definition is void"void-variable
"Symbol's value as variable is void"wrong-number-of-arguments
"Wrong number of arguments"wrong-type-argument
"Wrong type argument"
These kinds of error, which are classified as special cases of
arith-error, can occur on certain systems for invalid use of
mathematical functions.
domain-error
"Arithmetic domain error"overflow-error
"Arithmetic overflow error"range-error
"Arithmetic range error"singularity-error
"Arithmetic singularity error"underflow-error
"Arithmetic underflow error"The table below lists the general-purpose Emacs variables that automatically become buffer-local in each buffer. Most become buffer-local only when set; a few of them are always local in every buffer. Many Lisp packages define such variables for their internal use, but we don't try to list them all here.
abbrev-mode
auto-fill-function
buffer-auto-save-file-name
buffer-backed-up
buffer-display-count
buffer-display-table
buffer-file-format
buffer-file-name
buffer-file-number
buffer-file-truename
buffer-file-type
buffer-invisibility-spec
buffer-offer-save
buffer-read-only
buffer-saved-size
buffer-undo-list
cache-long-line-scans
case-fold-search
ctl-arrow
comment-column
default-directory
defun-prompt-regexp
enable-multibyte-characters
fill-column
goal-column
left-margin
local-abbrev-table
local-write-file-hooks
major-mode
mark-active
mark-ring
minor-modes
mode-line-buffer-identification
mode-line-format
mode-line-modified
mode-line-process
mode-name
overwrite-mode
paragraph-separate
paragraph-start
point-before-scroll
require-final-newline
selective-display
selective-display-ellipses
tab-width
truncate-lines
vc-mode
The following symbols are used as the names for various keymaps. Some of these exist when Emacs is first started, others are loaded only when their respective mode is used. This is not an exhaustive list.
Almost all of these maps are used as local maps. Indeed, of the modes that presently exist, only Vip mode and Terminal mode ever change the global keymap.
Buffer-menu-mode-map
c-mode-map
command-history-map
ctl-x-4-map
ctl-x-5-map
ctl-x-map
debugger-mode-map
dired-mode-map
dired-mode buffers.
edit-abbrevs-map
edit-abbrevs.
edit-tab-stops-map
edit-tab-stops.
electric-buffer-menu-mode-map
electric-history-map
emacs-lisp-mode-map
facemenu-menu
facemenu-background-menu
facemenu-face-menu
facemenu-foreground-menu
facemenu-indentation-menu
facemenu-justification-menu
facemenu-special-menu
function-key-map
fundamental-mode-map
Helper-help-map
Info-edit-map
Info-mode-map
isearch-mode-map
key-translation-map
function-key-map. See section Translating Input Events.
lisp-interaction-mode-map
lisp-mode-map
menu-bar-edit-menu
menu-bar-files-menu
menu-bar-help-menu
menu-bar-mule-menu
menu-bar-search-menu
menu-bar-tools-menu
mode-specific-map
display-bindings),
where it describes the main use of the C-c prefix key.
occur-mode-map
query-replace-map
query-replace and related
commands; also for y-or-n-p and map-y-or-n-p. The functions
that use this map do not support prefix keys; they look up one event at a
time.
text-mode-map
view-mode-map
The following is a list of hook variables that let you provide functions to be called from within Emacs on suitable occasions.
Most of these variables have names ending with `-hook'. They are
normal hooks, run by means of run-hooks. The value of such
a hook is a list of functions; the functions are called with no
arguments and their values are completely ignored. The recommended way
to put a new function on such a hook is to call add-hook.
See section Hooks, for more information about using hooks.
The variables whose names end in `-hooks' or `-functions' are usually abnormal hooks; their values are lists of functions, but these functions are called in a special way (they are passed arguments, or their values are used). A few of these variables are actually normal hooks which were named before we established the convention that normal hooks' names should end in `-hook'.
The variables whose names end in `-function' have single functions as their values. (In older Emacs versions, some of these variables had names ending in `-hook' even though they were not normal hooks; however, we have renamed all of those.)
activate-mark-hook
after-change-function
after-change-functions
after-init-hook
after-insert-file-functions
after-make-frame-hook
after-revert-hook
after-save-hook
auto-fill-function
auto-save-hook
before-change-function
before-change-functions
before-init-hook
before-make-frame-hook
before-revert-hook
blink-paren-function
buffer-access-fontify-functions
c-mode-hook
calendar-load-hook
change-major-mode-hook
command-history-hook
command-line-functions
comment-indent-function
deactivate-mark-hook
diary-display-hook
diary-hook
dired-mode-hook
disabled-command-hook
echo-area-clear-hook
edit-picture-hook
electric-buffer-menu-mode-hook
electric-command-history-hook
electric-help-mode-hook
emacs-lisp-mode-hook
find-file-hooks
find-file-not-found-hooks
first-change-hook
fortran-comment-hook
fortran-mode-hook
ftp-setup-write-file-hooks
ftp-write-file-hook
indent-mim-hook
initial-calendar-window-hook
kill-buffer-hook
kill-buffer-query-functions
kill-emacs-hook
kill-emacs-query-functions
LaTeX-mode-hook
ledit-mode-hook
lisp-indent-function
lisp-interaction-mode-hook
lisp-mode-hook
list-diary-entries-hook
local-write-file-hooks
m2-mode-hook
mail-mode-hook
mail-setup-hook
mark-diary-entries-hook
medit-mode-hook
menu-bar-update-hook
minibuffer-setup-hook
minibuffer-exit-hook
news-mode-hook
news-reply-mode-hook
news-setup-hook
nongregorian-diary-listing-hook
nongregorian-diary-marking-hook
nroff-mode-hook
outline-mode-hook
plain-TeX-mode-hook
post-command-hook
pre-abbrev-expand-hook
pre-command-hook
print-diary-entries-hook
prolog-mode-hook
protect-innocence-hook
redisplay-end-trigger-functions
rmail-edit-mode-hook
rmail-mode-hook
rmail-summary-mode-hook
scheme-indent-hook
scheme-mode-hook
scribe-mode-hook
shell-mode-hook
shell-set-directory-error-hook
suspend-hook
suspend-resume-hook
temp-buffer-show-function
term-setup-hook
terminal-mode-hook
terminal-mode-break-hook
TeX-mode-hook
text-mode-hook
today-visible-calendar-hook
today-invisible-calendar-hook
vi-mode-hook
view-hook
window-configuration-change-hook
window-scroll-functions
window-setup-hook
window-size-change-functions
write-contents-hooks
write-file-hooks
write-region-annotate-functions
Jump to: a - b - c - d - e - f - h - i - k - l - m - n - o - p - r - s - t - w
This usage of "key" is not related to the term "key sequence"; it means a value used to look up an item in a table. In this case, the table is the alist, and the alist associations are the items.
This definition of "environment" is specifically not intended to include all the data that can affect the result of a program.
Button-down is the conservative antithesis of drag.
They are not exactly equal because
right includes the vertical separator line or scroll bar, while
(window-width) does not.
This document was generated on 7 November 1998 using the texi2html translator version 1.52.