demerphq at gmail
Nov 13, 2006, 9:59 AM
Post #1 of 2
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[PATCH] Allow negative indexing in recursive patterns
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I noticed while trying to convert some code from using (??{}) to using
the new recursion syntax that there is a real need for the ability to
relatively address a given capture buffer.
Consider
our $parens;
$parens = qr/ \( (?: [^()]++ | (??{$qr}) )*+ \) /x;
if (/ foo $paren \s* , \s* bar $parens /x) { ... }
Is tricky to convert to recursion currently. So what I've done is Ive
allowed negative integers to be used so the above can be converted to
my $parens = qr/ \( (?: [^()]++ | (?-1) )*+ \) /x;
if (/ foo $paren \s* , \s* bar $parens /x) { ... }
So a negative (?PARNO) means to recurse the N'th capturing paren
before the use of the (?PARNO). Thus (?-1) is to recurse to the
immediately preceding open paren.
Similarly I put in support for a plus sign indicating relative forward
addressing, ie, execute the pattern contained in the nth following
buffer.
Attached patch includes documentation and tests for the new feature.
Its relative to my most recent patches as sent in, unfortunately
perl-current and perl-current-diffs are out of date right now so I
havent been able to synchronize up before I sent it in. Hope it
applies ok.
Cheers,
Yves
--
perl -Mre=debug -e "/just|another|perl|hacker/"
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relative_recursion.patch
