use Tk;

$w = MainWindow->new();

$w->Button(-text => 'Press me', -command => sub { doit() })->pack();

$qb = $w->Button(-text => 'Quit', -command => sub { exit() });

MainLoop();

sub doit {
	if ($qb->ismapped()) {
		$qb->packForget();
	} else {
		$qb->pack();
	}
}