#!/usr/bin/perl
use warnings;
use strict;
use Tk;

my $tl;
my $mw = MainWindow->new;
$mw->title( "MainWindow" );

my $spawn_button = $mw->Button( -text => "Toplevel", 
                -command => \&do_Toplevel )->pack();

MainLoop;

sub do_Toplevel {
        $spawn_button->configure(-state=>'disabled');

	if ( !Exists( $tl ) ) {
		$tl = $mw->Toplevel();
		
		$tl->protocol('WM_DELETE_WINDOW' => sub {
                     print "do nothing here\n"; #prevents destruction of $tl
		                                #by WM control
		 });
		
		$tl->geometry('300x100+100+100');
		$tl->title( "Toplevel" );
		$tl->Button(
			-text    => "Close",
			-command => sub { $tl->withdraw; 
			     $spawn_button->configure(-state=>'normal');
			     }
		)->pack;
	}
	else {
		$tl->deiconify();
		$tl->raise();
	}
}