use strict;
use Tk;

my $mw = MainWindow->new();

my $menubar = $mw->Menu(-type=>'menubar');
$mw->configure(-menu=>$menubar);
$menubar->cascade(-label => 'Datei',
                  -underline => 0
                 );
my $menu_datei = $menubar->Menu(-menuitems=>
                                [
                                 ['command' => 'Menupunkt1',
                                 -command => \&callback,
                                 ]
                                 ]
                                 );
$menubar->entryconfigure('Datei',-menu=>$menu_datei);

MainLoop();

sub callback {
    
my $neues_menu_datei = $menubar->Menu(-menuitems=>
                                        [
                                         ['command' => 'Anderer Menupunt',
                                          -command => \&callback2,
                                         ]
                                        ]
                                      );
                                      
$menubar->entryconfigure('Datei',-menu=>$neues_menu_datei);
}