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7.3 Changing the comment delimiters
===================================
The default comment delimiters can be changed with the builtin macro
`changecom':
-- Builtin: changecom ([START], [END])
This sets START as the new begin-comment delimiter and END as the
new end-comment delimiter. If only one argument is provided,
newline becomes the new end-comment delimiter. The comment
delimiters can be of any length. Omitting the first argument, or
using the empty string as the first argument, disables comments.
The expansion of `changecom' is void.
define(`comment', `COMMENT')
=>
# A normal comment
=># A normal comment
changecom(`/*', `*/')
=>
# Not a comment anymore
=># Not a COMMENT anymore
But: /* this is a comment now */ while this is not a comment
=>But: /* this is a comment now */ while this is not a COMMENT
Note how comments are copied to the output, much as if they were
quoted strings. If you want the text inside a comment expanded, quote
the begin-comment delimiter.
Calling `changecom' without any arguments, or with an empty string
for the first argument, disables the commenting mechanism completely.
To restore the original comment start of `#', you must explicitly ask
for it.
define(`comment', `COMMENT')
=>
changecom
=>
# Not a comment anymore
=># Not a COMMENT anymore
changecom(`#')
=>
# comment again
=># comment again
The comment strings can safely contain eight-bit characters.
Comments are recognized in preference to macros. However, this is
not compatible with other implementations, where macros and even quoting
takes precedence over comments, so it may change in a future release.
For portability, this means that START should not begin with a letter
or `_' (underscore), and that neither the start-quote nor the
start-comment string should be a prefix of the other.
define(`hi', `HI')
=>
changecom(`q', `Q')
=>
q hi Q hi
=>q hi Q HI
Comments are recognized in preference to argument collection. In
particular, if START is a single `(', then argument collection is
effectively disabled. For portability with other implementations, it
is a good idea to avoid `(', `,', and `)' as the first character in
START.
define(`echo', `$#:$@:')
=>
define(`hi', `HI')
=>
changecom(`(',`)')
=>
echo(hi)
=>0::(hi)
changecom
=>
changecom(`((', `))')
=>
echo(hi)
=>1:HI:
echo((hi))
=>0::((hi))
changecom(`,', `)')
=>
echo(hi,hi)bye)
=>1:HI,hi)bye:
It is an error if the end of file occurs within a comment.
changecom(`/*', `*/')
=>
/*dangling comment
^D
error-->m4:stdin:1: ERROR: end of file in comment
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