if ( $cool_stuff ) {
    my $foo = 0;
    my $bar = 42;
    $my_gui_object->add_callback( "<Neato_Event>",
                                  sub {
                                         my ($event, $argument) = ( @_ );
                                         if ( $argument == $bar ) {
                                             $foo++;
                                             return 1;
                                         }
                                         return 0;
                                       },
                                 );
    $my_gui_object->add_callback( "<WayCool_Event>",
                                  sub {
                                         my ($event, $argument) = ( @_ );
                                         if ( $argument == $bar ) {
                                             $foo--;
                                             return 1;
                                         }
                                         return 0;
                                       },
                                 );
}