use strict;
use warnings;
use Tk;
my $mw = MainWindow->new();
my $entry1 = $mw->Entry()->pack();
my $entry2 = $mw->Entry()->pack();
my $entry3 = $mw->Entry()->pack();

my %after = ($entry1 => $entry2,
             $entry2 => $entry1,
          );

$mw -> bind('all','<Tab>',sub{
				($after{$_[0]})->focus;
			}
			);
								
$mw->MainLoop();
exit(0);


##</code><code>##

Tk::Error: Can't call method "focus" on an undefined value at C:\Users\FC\Desktop\Entry.pl line 14.
 <Key-Tab>
 (command bound to event)