my $change_mode = \&change_mode;
...
# Case 2:  Callback routine called with argument (corrected):
# given that $change_mode is a ref to a sub
$main->Button(-text => 'To Upper Case',
              -command => [ $change_mode, 2 ]
              )->pack;
[download]

The "bind" case is a little different, because the sub will actually get the widget handle that invoked it as the first arg every time a "bound" event triggers the sub, whereas the "-command" option does not pass the widget handle as the first arg.

Well, that's a style I don't see everyday, but perldoc Tk::callbacks says exactly that - use the array reference and this can be done as shown.

--Bob Niederman, http://bob-n.com

# generate a closure:
sub gen_change_mode {
    my $mode = shift;
    return {
        # same code as in change_mode

    };
}

# then do this
$main->Button(-text => 'To Upper Case',
    -command => gen_change_mode(2)
    )->pack;

# or this
$some_ref = gen_change_mode(3);

$main->Button(-text => 'To Mixed Case',
    -command => $some_ref
    )->pack;
[download]

so in the last case gen_change_mode(3) will return a code reference with $mode set as 3, meaning you can pass this around as a code ref, which is what you're after.

there is an example in `perldoc perlref` which uses a lexical (my) var inside the anon sub that gets returned, so you can pass more arguments to it when you finally run it as a subroutine.

Yes. Otherwise, it'd be Very Hard to determine automatically whether you meant a subroutine call to execute now or at some point in the future.

I'm pretty sure that's right. There was another node about that recently.