use Tk;
my $top = new MainWindow;
$top->Scrolled("Listbox")->pack->insert("end", keys %ENV);
$top->Scrolled("Listbox")->pack->insert("end", keys %INC);
my $c = $top->Scrolled( qw/Canvas
            -width 400 -height 400 -relief sunken
         -bg white -borderwidth 1 -scrollbars se -scrollregion/ => 
                 [qw/0 0 1000 1000/])->pack;
 $top->bind($top, '<MouseWheel>', 
        [sub { my $unit = $_[1] > 0 ? -1 : 1;
               $c->yviewScroll($unit => 'units')
           },
         Ev('D')]
);
MainLoop;