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From: cwitty@csli.Stanford.EDU (Carl Witty)
Newsgroups: comp.lang.perl
Subject: Re: Matching parentheses
Message-ID: <16600@csli.Stanford.EDU>
Date: 29 Nov 90 00:53:58 GMT
References: <1990Nov28.150131.28981@ugle.unit.no>
Sender: cwitty@csli.Stanford.EDU
Organization: CSLI, Stanford University
Lines: 22
In-reply-to: harald.alvestrand@elab-runit.sintef.no's message of 28 Nov 90 15:01:31 GMT

In article <1990Nov28.150131.28981@ugle.unit.no> harald.alvestrand@elab-runit.sintef.no writes:

   I have thought a long time about this, but I am sure there must be some
   magic way to do it:
   How can I write a pattern that matches (), ((())), ((())()), but NOT ((())?
   That is, how do I get a balanced matching of parentheses?

There is no pattern that will do it, but here's a program that will.

#!/afs/ir/@sys/local/bin/perl
while (<STDIN>) {
  chop;
  while (s/\(\)//) {}
  if ($_ eq "") {
    print "Balanced\n";
  } else {
    print "Unbalanced\n";
  }
}

Carl Witty
cwitty@cs.stanford.edu