#!/usr/bin/perl
use strict;
use warnings;
use Tk;
use Regexp::Common qw/number/;

my $top = MainWindow->new();
$top->geometry('300x200');

$top->fontCreate('big',
   -family=>'courier',
  -weight=>'bold',
  -size=>int(-18*18/14));

my %entries;
my $current = 1;

for(1..4){
 $entries{$_}{'value'} ||= '';
 $entries{$_}{'entry'} = $top->Entry(
      -font => 'big',
      -textvariable => \$entries{$_}{'value'},
      -width        => 2,
      -validate     => 'key',
      -vcmd         => \&validate,
  )->pack(-side =>'left',-padx => 5);
}

$entries{$current}{'entry'}->focus;
MainLoop;

sub validate{
  my $val = shift;

  if( $val =~  /^$RE{num}{real}{-base=>'16'}$/ ) { 
     if( length $val == 2){
                print "2\n";
                $current++;
		if($current > 4){$current = 4} 
		$entries{$current}{'entry'}->focusForce;
		$top->update;
		}
      return 1;
    }

return 0;

}