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From: lwall@jpl-devvax.jpl.nasa.gov (Larry Wall)
Newsgroups: comp.lang.perl
Subject: Re: recursive &func breaks s/(foo)/&func($1)/eg
Message-ID: <1991Mar13.185951.15222@jpl-devvax.jpl.nasa.gov>
Date: 13 Mar 91 18:59:51 GMT
References: <5128@atexnet.UUCP>
Reply-To: lwall@jpl-devvax.JPL.NASA.GOV (Larry Wall)
Organization: Jet Propulsion Laboratory, Pasadena, CA
Lines: 24

In article <5128@atexnet.UUCP> lawrence@epps.kodak.com (Scott Lawrence) writes:
: I think that I have discovered a problem with substitution and
: recursion.  Please someone demonstrate that I am wrong.

You're right, but you'll be wrong when 4.0 comes out.  :-)

When you do a pattern match, the regular expression routines sometimes
save a copy of the input string so that $1, $&, etc. work right after
the pattern match.  The substitution operator was depending on this
string to stay there so that it could continue the substitution using
the value of $', more or less.  Unfortunately, the recursion clobbered
that temporary value.  The do_subst() routine just needed to make sure
it could restore $' after evaluating the right-hand side, and I figured
out a way to do that by manipulating the pointers, so I don't have to
actually copy the contents of $' around.

Note, however that order of evaluation will still be important.  If you say

	s/(whatever)/&recurse($1) . $1/eg;

The first $1 refers to the $1 from this substitution, while the second $1
refers to the $1 from pattern match done within &recurse.  (I think.)

Larry