Re: Using qw to check for balanced parentheses

It doesn't appear to work?

$ perl -le'
sub is_balanced {
   my $string = shift;

   eval("qw($string)");
   return 0 if @$;
   return 1;
}
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 $balanced balanced? %s\n", is_balanced($balanced) ? "yes" :
+ "no");
printf("Is $unbalanced1 balanced? %s\n", is_balanced($unbalanced1) ? "
+yes" : "no");
printf("Is $unbalanced2 balanced? %s\n", is_balanced($unbalanced2) ? "
+yes" : "no");
'
Is (1 + 2 * (3 + (5/4) + 8) + 6) balanced? yes
Is (((1 + 2 * (3 + (5/4) + 8) + 6)) balanced? yes
Is (((1 + 2 * (3 + (5/4) + 8) + 6)))) balanced? yes
[download]

Comment on Re: Using qw to check for balanced parentheses Download Code

Replies are listed 'Best First'.
Re^2: Using qw to check for balanced parentheses by Anonymous Monk on Feb 01, 2011 at 23:16 UTC
typo `@$;` is not `$@;`	[reply] [d/l] [select]
Re^3: Using qw to check for balanced parentheses by jwkrahn (Abbot) on Feb 02, 2011 at 01:08 UTC
Yes, that works a lot better. `:-)` Of course, the subroutine could be reduced to just: `sub is_balanced { eval "qw($_[0])" }` [download] And it will also work with `qq` as well as with `qw`. $ perl -le' sub is_balanced { eval qq($_[0]) } 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))))"; print "Is $balanced balanced? ", is_balanced( $balanced ) ? "yes" : "n +o"; print "Is $unbalanced1 balanced? ", is_balanced( $unbalanced1 ) ? "yes +" : "no"; print "Is $unbalanced2 balanced? ", is_balanced( $unbalanced2 ) ? "yes +" : "no"; ' Is (1 + 2 * (3 + (5/4) + 8) + 6) balanced? yes Is (((1 + 2 * (3 + (5/4) + 8) + 6)) balanced? no Is (((1 + 2 * (3 + (5/4) + 8) + 6)))) balanced? no [download]	[reply] [d/l] [select]
Re^4: Using qw to check for balanced parentheses by ikegami (Patriarch) on Feb 02, 2011 at 02:00 UTC
That won't handle `""` hand `"0"`, but that's easy to fix: `sub is_balanced { eval "qw($_[0]); 1" }` [download]	[reply] [d/l] [select]
Re^4: Using qw to check for balanced parentheses by Anonymous Monk on Feb 02, 2011 at 01:13 UTC
`sub is_balanced2 { not $_[0] =~ tr/)(// % 2; }`	[reply] [d/l]
Re^5: Using qw to check for balanced parentheses by Your Mother (Archbishop) on Feb 02, 2011 at 01:29 UTC
Re^6: Using qw to check for balanced parentheses by Anonymous Monk on Feb 02, 2011 at 01:46 UTC
Re^3: Using qw to check for balanced parentheses by unix_hacker_beard (Novice) on Feb 02, 2011 at 01:27 UTC
D'oh! Thanks, I'm too used to dereferencing arrays.	[reply]
Re^2: Using qw to check for balanced parentheses by Anonymous Monk on Oct 23, 2014 at 16:07 UTC
I may be mistaken, but this does not detect a case like "}a{" , or does it? how about `sub balanced { (my $s = shift) =~ s/[^()]//g; while ( $s =~s /// ){}; return $s ? 0 : 1; }` [download] ? It may be slower, but detects ')(' as incorrect	[reply] [d/l]