On Monday 06 April 2009 08:59:32 Eric Blake wrote: > According to Mike Frysinger on 4/5/2009 7:19 PM: > >> i'm not an expert by any means with internal autoconf/m4. if there's a > >> m4 helper function to test whether an argument contains something other > >> than whitespace, then the change to m4sh.m4:_AS_IF is trivial ... use > >> that rather than m4_ifvaln([$1],.... > > > > to answer my own question and to post a patch, m4_normalize can be used: > > Indeed. However, m4_normalize is an expensive choice for doing this check > (it involves regular expressions). I'm thinking of introducing a new > m4sugar macro (untested in this email) that can be used for this purpose > with less overhead - any suggestions for a better name? "blank" is actually what i thought of at first when i went looking for a preexisting function ;) > # m4_ifblank(COND, [IF-BLANK], [IF-TEXT]) > # --------------------------------------- > # If COND is empty, or consists only of blanks (space, tab, newline), > # expand IF-BLANK, else expand IF-TEXT. > m4_define([m4_ifblank], > [m4_if(m4_translit([[$1]], [ ][ ][ > ]), [], [$2], [$3])]) > > Hmm, this means that in addition to differing on a COND consisting of just > whitespace, m4_ifval and m4_ifblank have opposite if-then sense: > m4_ifval([$1], [$1], []) > m4_ifblank([$1], [], [$1]) call it m4_ifnblank() ? or have both so people can swap as needed ? i imagine people would favor the form for their specific case which only requires one argument. i know i would. m4_ifblank(COND, [IF-BLANK], [IF-TEXT]) m4_ifnblank(COND, [IF-TEXT], [IF-BLANK]) > > this should "fix" every macro that uses AS_IF with an "else" argument. > > it certainly fixes my test case. > > I think you are right that fixing AS_IF to detect blank instead of empty > arguments when performing optimizations will probably help a number of > poorly-written configure.ac, so I will probably be checking in a patch > along these lines soon. Note, however, that this still doesn't help > situations like: > > AS_IF([foo], [AC_REQUIRE([bar])]) > > since the presence of AC_REQUIRE will trigger the IF-TEXT expansion, > although the subsequent expansion pass will result in a blank body. true, although i dont really know squat about m4 to propose any solution along those lines. perhaps have the else case always emit a leading null cmd ":" ? seems like adding 2 bytes is a small price to pay for the resulting syntax safety ... --- a/lib/m4sugar/m4sh.m4 +++ b/lib/m4sugar/m4sh.m4 @@ -607,7 +607,7 @@ m4_define([_AS_IF], ]) m4_define([_AS_IF_ELSE], [m4_ifvaln([$1], -[else +[else : $1])]) m4_defun([AS_IF], -mike
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