#!/usr/bin/env perl
 
use English;
require Tk;
use Tk;

use Tk;

my $mw = MainWindow->new();

my $entry = $mw->Entry()->pack();
$entry->configure( -textvariable => \$content , 
      -validate => 'key' ,
      -validatecommand => sub { 
                                      
              my $newvalue     = shift;
              my $changedchars = shift;
              my $currentvalue = shift;
              my $index        = shift;
              my $type         = shift;
                    
    print "newval-> $newvalue\nchangedchars-> $changedchars\n".
    "curvalue-> $currentvalue\n index-> $index\n\n\n";


   if( ($index == 0) and ($newvalue ne 'g')){return 0}
   if( ($index == 1) and ($newvalue ne 'go')){return 0}
   if( ($index == 2) and ($newvalue ne 'go ')){return 0}

   return 1;
            
         },
   -invalidcommand => [ \&errorsub , \$entry ]
        ) ;

MainLoop;

sub errorsub { 
        print "ERROR.\n"; 
        $content = "" ;
        $entry->focus;
        $entry->icursor(0);
        }