use Tk;
use Tk::MListbox;

my $mw = MainWindow->new();
my $count_v = 0;
my $stop_v = 0;

my $stop = $mw->Checkbutton(-text => "stop", -variable => \$stop_v, -command => \&schedule)->pack();
my $count = $mw->Label(-text => $count_v)->pack();
$count->after(1000, \&inc);

MainLoop;

sub inc {
	$count->configure(-text => $count->cget("-text") + 1);
	if (!$stop_v) {
		$count->after(1000, \&inc);
	}
}

sub schedule {
	if (!$stop_v) {
		$count->after(1000, \&inc);
	}
}