(m4.info.gz) Macro Arguments
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3.3 Macro arguments
===================
When a name is seen, and it has a macro definition, it will be expanded
as a macro.
If the name is followed by an opening parenthesis, the arguments
will be collected before the macro is called. If too few arguments are
supplied, the missing arguments are taken to be the empty string.
However, some builtins are documented to behave differently for a
missing optional argument than for an explicit empty string. If there
are too many arguments, the excess arguments are ignored. Unquoted
leading whitespace is stripped off all arguments.
Normally `m4' will issue warnings if a builtin macro is called with
an inappropriate number of arguments, but it can be suppressed with the
`--quiet' command line option (or `--silent', or `-Q', Invoking
m4). For user defined macros, there is no check of the number of
arguments given.
Macros are expanded normally during argument collection, and whatever
commas, quotes and parentheses that might show up in the resulting
expanded text will serve to define the arguments as well. Thus, if FOO
expands to `, b, c', the macro call
bar(a foo, d)
is a macro call with four arguments, which are `a ', `b', `c' and `d'.
To understand why the first argument contains whitespace, remember that
leading unquoted whitespace is never part of an argument, but trailing
whitespace always is.
It is possible for a macro's definition to change during argument
collection, in which case the expansion uses the definition that was in
effect at the time the opening `(' was seen.
define(`f', `1')
=>
f(define(`f', `2'))
=>1
f
=>2
It is an error if the end of file occurs while collecting arguments.
define(
^D
error-->m4:stdin:1: ERROR: end of file in argument list
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