8.1.2 One Macro Call

Let's proceed on the interaction between active characters and macros with this small macro, which just returns its first argument:

define([car], [$1])

The two pairs of quotes above are not part of the arguments of define; rather, they are understood by the top level when it tries to find the arguments of define. Therefore, it is equivalent to write:

define(car, $1)

But, while it is acceptable for a `configure.ac' to avoid unnecessary quotes, it is bad practice for Autoconf macros which must both be more robust and also advocate perfect style.

At the top level, there are only two possibilities: either you quote or you don't:

car(foo, bar, baz) =>foo [car(foo, bar, baz)] =>car(foo, bar, baz)

Let's pay attention to the special characters:

car(#) error-->EOF in argument list

The closing parenthesis is hidden in the comment; with a hypothetical quoting, the top level understood it this way:

car([#)]

Proper quotation, of course, fixes the problem:

car([#]) =>#

The reader will easily understand the following examples:

car(foo, bar) =>foo car([foo, bar]) =>foo, bar car((foo, bar)) =>(foo, bar) car([(foo], [bar)]) =>(foo car([], []) => car([[]], [[]]) =>[]

With this in mind, we can explore the cases where macros invoke macros....