#!/usr/bin/perl -w
use strict;
my @strings = ( '(a(a(b)a)a)',         # balanced
                '(a(a(b)a)a)a)',       # too many right parens
                '(a(a(b)a\)a)a)',      # balanced -- one right paren is escaped
                '(a(a\(a(a(b)a)a)',    # unbalanced -- still have too many left parens
                '(a(a\(a(b)a)a)' );    # balanced -- one left paren is escaped
foreach my $string ( @strings ) {
    my $balanced = balanced_delimiters( $string, "(", ")", "\\" );
    print "Delimiters in $string are ";
    if ( $balanced ){
        print "balanced.\n";
    } else {
        print "not balanced.\n";
    } 
}
sub balanced_delimiters {
    # $escape is optional.  If not supplied, no escape character will
    # be recognized.
    my $str    = shift;
    my $left   = quotemeta shift;
    my $right  = quotemeta shift;
    my $escape = quotemeta shift;
    my $unescapedLeft  = "(?<!$escape)$left";
    my $unescapedRight = "(?<!$escape)$right";
    my $middle = ".";  # AAARRRRGGGGHHHH!!!!
    my $regex  = "$unescapedLeft($middle*?)$unescapedRight";
    while ($str =~ s/$regex/$1/gs){};
    return $str =~ /$unescapedLeft|$unescapedRight/ ? 0 : 1;
}