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Re: Re: A demanding parser

by TheDamian (Priest)
on Jan 25, 2002 at 17:12 UTC ( #141489=note: print w/ replies, xml ) Need Help??


in reply to Re: A demanding parser
in thread A demanding parser

Is there any way of avoiding the external module and catch an arbitrary number of nested parentheses with a "normal" Regex?
use Regexp::Common; $str =~ /$RE{balanced}{-parens=>'()'}/


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Re: Re: Re: A demanding parser
by Juerd (Abbot) on Jan 25, 2002 at 20:34 UTC
    That's what he does already. He asked if it were possible without the module. (Not a very good idea, but I don't know the motivation (education, perhaps))

    2;0 juerd@ouranos:~$ perl -e'undef christmas' Segmentation fault 2;139 juerd@ouranos:~$

      Ah, sorry. Missed that bit.

      How about:

      use Regexp::Common; print $RE{balanced}{-parens=>'()'}, "\n"; print $RE{balanced}{-parens=>'{}'}, "\n"; print $RE{balanced}{-parens=>'{}()'}, "\n"; # etc.
      followed by reading the Regexp::Common source?

      Damian

        It works! I had some trouble figuring out how to implement it, because with 'use strict' the recursive RegEx stays undefined.
        #!/usr/bin/perl -w use strict; my $input = "aa (bb cc) dd (ee (ff (gg) hh) jj) kk ((ll)) mm"; no strict 'vars'; # from $RE{balanced}{-parens=>'()'}; $REparens = qr/ (?:(?:(?:[(](?:(?>[^)(]+) |(??{$REparens}))*[)])) |(?:(?!)))/x; my $re = $REparens; use strict; print "input: $input\n"; while ($input =~ /\G(\w+|$re)\s*/gc) { print "$1\n" } __END__ output: aa (bb cc) dd (ee (ff (gg) hh) jj) kk ((ll)) mm
        Making a block of no strict 'vars' solves the problem. There I can assign the recursive regex to a proper ly declared variable, or call explicitly ($main::REparens).
        Thanks a million.
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