11. Variables

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 8.1 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.

11.1 Global Variables		Variable values that exist permanently, everywhere.
11.2 Variables that Never Change		Certain "variables" have values that never change.
11.3 Local Variables		Variable values that exist only temporarily.
11.4 When a Variable is "Void"		Symbols that lack values.
11.5 Defining Global Variables		A definition says a symbol is used as a variable.
11.6 Tips for Defining Variables Robustly		Things you should think about when you define a variable.
11.7 Accessing Variable Values		Examining values of variables whose names are known only at run time.
11.8 How to Alter a Variable Value		Storing new values in variables.
11.9 Scoping Rules for Variable Bindings		How Lisp chooses among local and global values.
11.10 Buffer-Local Variables		Variable values in effect only in one buffer.
11.11 Frame-Local Variables		Variable values in effect only in one frame.
11.12 Possible Future Local Variables		New kinds of local values we might add some day.
11.13 File Local Variables		Handling local variable lists in files.