-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 According to Akim Demaille on 4/24/2008 3:20 AM:
[dropping bug-bison, adding m4-discuss] |> Really, the problem is |> that there is no way to determine whether $1 is safe to expand, short of |> expanding $1; thus, if it was not safe, you've already screwed up the |> state of the m4 parsing. | | I always felt m4 lacks an "eval" macro. Not the one for arithmetics, | but one which would run m4 on its argument, and return the expansion | quoted. This is what tried to do m4_quote/m4_dquote, but it's fragile. | | There are really two sort of macros. Those which really work on the | text, and you do not want to evaluate the result. This is where | regexp, patsubst etc. live. And there are the regular just-expanding | macros. And macros such as substr are practically worthless as is in a harsh environment - they operate on text and return an unquoted result, which is almost never what you want if you don't want the result immediately expanded. | | For the latter, a usual single-level of quotation is fine. For the | former, we need two. And we have no safe means to go from one model | to the other, between text-hacking macros and text-expanding macros. | | Something like a new primitive "eval and return quoted" would fill | the gap. | | Well, at least that's what I believed years ago :) | Yes, m4 has a TODO item about adding the qindir builtin (and which I will probably do for m4 1.6). The original request mentioned making it robust even in the face of unbalanced quotes inside the text, but I don't know if I can make the m4 machinery do that. But I can quite easily make it behave exactly like indir except for the addition of an additional level of quotes in the output. Then you will have (in m4sugar quoting): m4_define([m4_qsubstr], [m4_qindir([m4_substr], $@)]) such that m4_define([b], [HI]) m4_substr([abc], [1], [1]) => HI m4_qsubstr([abc], [1], [1]) => b - -- Don't work too hard, make some time for fun as well! Eric Blake [EMAIL PROTECTED] -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (Cygwin) Comment: Public key at home.comcast.net/~ericblake/eblake.gpg Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iEYEARECAAYFAkgQfS0ACgkQ84KuGfSFAYBCIACg2VSyZFfYlLIKLN4z3QThfl87 aIQAoLRZHqhTqWFhnqsQ4QBlu4+e5Ujx =ZGvN -----END PGP SIGNATURE----- _______________________________________________ m4-discuss mailing list m4-discuss@gnu.org http://lists.gnu.org/mailman/listinfo/m4-discuss
