use Tk;

my $mw = new MainWindow;

my $b = $mw->Button(-text => 'Run')->pack(-fill => 'x');

my $id;
my $i;

$b->bind('<ButtonPress-1>' => sub { $i = 0;
                                    $id = $mw->repeat(2, sub {print ++$i, "\n"}) } );
$b->bind('<ButtonRelease-1>' => sub { $id->cancel() } );

MainLoop();