#!/usr/bin/perl
use warnings;
use strict;
use Tk;

my $FILTER_IS_ON = 0;

my $top = new MainWindow();

my $c1 = $top->Button(-text=>$FILTER_IS_ON ? 'turn off' : 'turn on',
   -command => \&turn)->pack();

my $c2 = $top->Button(-text=> 'Go', 
 -state => 'disabled',
 -command => sub { print "ook!\n" })->pack();


MainLoop();

sub turn {
   $FILTER_IS_ON = $FILTER_IS_ON ? 0 : 1;
   $c1->configure(-text=> $FILTER_IS_ON ? 'turn off' : 'turn on');
   $c2->configure(-state=> $FILTER_IS_ON ? 'normal' : 'disabled');
}