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

use Tk;

my $main = tkinit;
$main->Label(-text => 'Hallo')->pack();
$main->Button(-text => 'change', -command => \&foo)->pack();

MainLoop();

sub foo {
$main->destroy();
$main = tkinit;
$main->Label(-text => 'blubb')->pack();
}