m4: Quoting Arguments
4.4 On Quoting Arguments to macros
==================================
Each argument has unquoted leading whitespace removed. Within each
argument, all unquoted parentheses must match. For example, if FOO is a
macro,
foo(() (`(') `(')
is a macro call, with one argument, whose value is '() (() ('. Commas
separate arguments, except when they occur inside quotes, comments, or
unquoted parentheses. ⇒Pseudo Arguments, for examples.
It is common practice to quote all arguments to macros, unless you
are sure you want the arguments expanded. Thus, in the above example
with the parentheses, the 'right' way to do it is like this:
foo(`() (() (')
It is, however, in certain cases necessary (because nested expansion
must occur to create the arguments for the outer macro) or convenient
(because it uses fewer characters) to leave out quotes for some
arguments, and there is nothing wrong in doing it. It just makes life a
bit harder, if you are not careful to follow a consistent quoting style.
For consistency, this manual follows the rule of thumb that each layer
of parentheses introduces another layer of single quoting, except when
showing the consequences of quoting rules. This is done even when the
quoted string cannot be a macro, such as with integers when you have not
changed the syntax via 'changeword' (⇒Changeword).
The quoting rule of thumb of one level of quoting per parentheses has
a nice property: when a macro name appears inside parentheses, you can
determine when it will be expanded. If it is not quoted, it will be
expanded prior to the outer macro, so that its expansion becomes the
argument. If it is single-quoted, it will be expanded after the outer
macro. And if it is double-quoted, it will be used as literal text
instead of a macro name.
define(`active', `ACT, IVE')
=>
define(`show', `$1 $1')
=>
show(active)
=>ACT ACT
show(`active')
=>ACT, IVE ACT, IVE
show(``active'')
=>active active
Info Catalog
m4: Macro Arguments
m4: Macros
m4: Macro expansion