Hello Monks

I need to monitor if a new element has been programmatically added to a Listbox. If a new element has been added, a subroutine should be called. Since I am not aware of any callback for this, in the script below, I try to use programmatically select a Listbox element with selectionSet (whenever a new element is added) in order to let the <<ListboxSelect>> call a subroutine. The approach does not work, since <<ListboxSelect>> seems to be called only if a Listbox element is selected by the user. Using <<Modified>> does not work too.

Any suggestion on how I could solve this?

use strict;
use warnings;
use Tk;
 
my $mw = MainWindow->new();
my $lbox = $mw->Listbox()->pack();
 
my @list = ( "a", "b", "c", "d", "e", "f" );
$lbox->insert('end', @list );

$lbox->selectionSet('1');

#$mw->Button(-text => "Set!", -command=>sub{$lbox->selectionSet('2');}
+)->pack();#to test if sectionSet works with <<ListboxSelect>> 

$lbox->bind('<<ListboxSelect>>', sub{warn "ListBox changed\n"} );

$mw->MainLoop;
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EDIT

The code above is in Perl/Tk and not in Tcl::Tk simply because I was looking for a solution independently of Tcl::Tk, as I thought a callback triggered by a state change in the Listbox was easier/possible to achieve then working on the Tcl bridge to Perl through Tcl::Tk (or the similar Tcl::pTk)