Path: utzoo!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!elroy.jpl.nasa.gov!jpl-devvax!lwall
From: lwall@jpl-devvax.jpl.nasa.gov (Larry Wall)
Newsgroups: comp.lang.perl
Subject: Re: Perl-Users Digest #651
Message-ID: <1991Mar11.224901.26872@jpl-devvax.jpl.nasa.gov>
Date: 11 Mar 91 22:49:01 GMT
References: <1991Mar9.230553.22037@uvaarpa.Virginia.EDU>
Reply-To: lwall@jpl-devvax.JPL.NASA.GOV (Larry Wall)
Organization: Jet Propulsion Laboratory, Pasadena, CA
Lines: 29

In article <1991Mar9.230553.22037@uvaarpa.Virginia.EDU> Marc Horowitz <marc@MIT.EDU> writes:
: |> From: tchrist@convex.COM (Tom Christiansen)
: |> 
: |> From the keyboard of emv@ox.com (Ed Vielmetti):
: |> :Speaking of which, what's the limits on the number of parentheses that
: |> :a regular expression can have?  I got an unpleasant message
: |> :
: |> :/^(scan)\s+((-(\w*))|)\s*\+(\w*)((s+((||>)(.*)))|)/: too many () in regexp at /u:1/emv/bin/smoke line 167, <> line 1.
: |> 
: |> Nine.  To accept more, Larry would have to change the code that
: |> recognizes \1 .. \9 and $1 .. .$9.
: |> 
: |> --tom
: 
: Ok, that explains it, but it doesn't excuse it.  Sometimes I want to
: match an expression complex enough (like Ed's example) that I need
: more than nine () to group everything.  In this case, perl should
: still work, and I would say that the regexp in an array context should
: contain as many elements as paren pairs, but that $1 .. $9 should
: contain the first nine () matches.

There's actually no syntactic reason we can't have $10 and higher, but
\10 already means a backspace.  Implementation-wise, Henry's regexp package
has a hardwired limit of 9, and fixing that will entail changing the
way the pattern-matching opcodes are set up, and this is non-trivial,
I think.  I kludged around this when adding {n,m}, and maybe I'll just
kludge it again.  Sigh.  I agree that the limit shouldn't be there.

Larry