I was playing around with qw today and it got me thinking... I'm probably not the first one to do this but I couldn't find it anywhere else. This works since qw can take any non-alphanumeric separator. 

sub is_balanced {
   my $string = shift;

   eval("qw($string)");
   return 0 if $@;
   return 1;
}

[download]

Here it is in action: 

my $balanced   = "(1 + 2 * (3 + (5/4) + 8) + 6)";
my $unbalanced1 = "(((1 + 2 * (3 + (5/4) + 8) + 6))";
my $unbalanced2 = "(((1 + 2 * (3 + (5/4) + 8) + 6))))";

printf("Is $balanced balanced? %s\n", balanced_parens($balanced) ? "ye
+s" : "no");
printf("Is $unbalanced1 balanced? %s\n", balanced_parens($unbalanced1)
+ ? "yes" : "no");
printf("Is $unbalanced2 balanced? %s\n", balanced_parens($unbalanced2)
+ ? "yes" : "no");

[download]

prints: 

Is (1 + 2 * (3 + (5/4) + 8) + 6) balanced? yes
Is (((1 + 2 * (3 + (5/4) + 8) + 6)) balanced? no
Is (((1 + 2 * (3 + (5/4) + 8) + 6)))) balanced? no

[download]

In reply to Using qw to check for balanced parentheses by unix_hacker_beard

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