that @constants will contain numbers and that you'll be checking whether or not a constant by that name exists...which it won't.

Hmm, well maybe my function doesn't do what the OP requested (quite possible since it was written pre-1pm ;) but it will do what I intended - given a list of strings return if they exist in a given package e.g

sub UNIVERSAL::which_constants {
  my($class, @constants) = @_;

  return grep exists $constant::declared{"$class\::$_"}, @constants;
}

use constant FOO => "a string";
use constant BAR => [ qw/ an array / ];
use constant BAZ => { qw/ a hash / };

print "constant exists - $_\n"
  for main->which_constants( qw/ ichi FOO bar BAZ one DEUX / );

__output__

constant exists - FOO
constant exists - BAZ
[download]

And if you want to go from constant values to constant names then check out chromatic's Devel::Constants module.
HTH

_________
broquaint