# Constants.pm
package Constants;

use constant XX       => 0;
use constant YY       => 1;

our @EXPORT = qw(XX YY);
1;

##</code><code>##

# caller.pl
use strict;
use warnings;
use Tk;
use Constants;

print "sum =",XX + YY,"\n";

##</code><code>##

use base qw(Exporter DynaLoader);