Re: m4 comment bug

[Gary V. Vaughan]

Hi David,

David A. Caplan wrote:
> m4 seems to be picking up single quote characters (') within comment
> lines (both when using # and dnl).  I am using "GNU m4 1.4.1". It also
> expands $1, $2,... if they are within a comment.
> 
> Example:
> define(`foo',`
> # there aren't any arguments to this macro
> this is output of the fo`o' macro')
> foo

I can see 3 problems with this code:

1. The m4 reader breaks tokens up on quote pairs (among others) before it
   starts any parsing, though it strips outer quotes almost immediately:

    token1: define
    token2: (
    token3: foo     {quotes are stripped)
    token4: \n#there aren
    token5: t any arguments to this macro\nthis is output of the foo macro'
    token6: )

   Note that token4 is considered complete when a matching ' character is
   read; token 5 has an unbalanced ' character, and the quotes inside foo
   are stripped because they are a matching outer pair.

   You have to change the quote characters to stop the reader treating
   your unbalanced ' as a close quote

2. Trying to partially quote fo`o' doesn't work at the outer level either,
   because by the time the reader has passed the token to the parser, those
   outer quotes have been stripped and foo is rescanned for macros (and
   hence expanded).  Double quoting literals is the standard way to make
   that work in m4.

3. The comment characters only apply at the outermost level, arguments to
   macro invocations are rescanned and expanded just like everything else.
   (and positional parameters are expanded too).

Here is an example of how to use all this:

  changequote([,])
    =>
  define([foo], [[
  # there aren't any arguments to foo
  this is output of the foo macro]])
    =>
  # foo
    => # foo
  foo
    => # there aren't any arguments to foo
       this is output of the foo macro

HTH,
        Gary.
-- 
Gary V. Vaughan      ())_.  address@hidden,gnu.org}
Research Scientist   ( '/   http://tkd.kicks-ass.net
GNU Hacker           / )=   http://www.gnu.org/software/libtool
Technical Author   `(_~)_   http://sources.redhat.com/autobook

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