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5.8 Indirect call of builtins
Builtin macros can be called indirectly with `builtin':
-- Builtin: builtin (NAME, [ARGS...])
Results in a call to the builtin NAME, which is passed the rest of
the arguments ARGS. If NAME does not name a builtin, an error
message is printed, and the expansion is void.
The macro `builtin' is recognized only with parameters.
This can be used even if NAME has been given another definition that
has covered the original, or been undefined so that no macro maps to
builtin(`define', `foo', defn(`divnum'))
builtin(`define', `foo', `BAR')
The NAME argument only matches the original name of the builtin,
even when the `--prefix-builtins' option (or `-P', *note Invoking m4:
Operation modes.) is in effect. This is different from `indir', which
only tracks current macro names.
$ m4 -P
error-->m4:stdin:2: undefined builtin `m4_divnum'
error-->m4:stdin:3: undefined macro `divnum'
Note that `indir' and `builtin' can be used to invoke builtins
without arguments, even when they normally require parameters to be
recognized; but it will provoke a warning, and result in a void
error-->m4:stdin:2: undefined builtin `'
error-->m4:stdin:3: Warning: too few arguments to builtin `builtin'
error-->m4:stdin:4: undefined builtin `'
error-->m4:stdin:5: undefined builtin ``'
error-->m4:stdin:7: Warning: too few arguments to builtin `index'
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