#!/usr/bin/perl -w

use strict;
my ($main);

# use Tk;			#=NIS=#
# $main = MainWindow->new();	#=NIS=#

use Tcl::Tk qw(:perlTk);	#=MBVK=#
my $interp = Tcl::Tk->new();	#=MBVK=#
$main = $interp->mainwindow();  #=MBVK=#

my ($n1, $add, $n2, $eq, $result);

$n1 = $main->Entry(-width=>3);
$add = $main->Label(-text=>" + ");
$n2 = $main->Entry(-width=>3); 
$eq = $main->Button(-text=>" = ", -command=>\&do_it);
$result = $main->Label(-width=>4);

foreach ($n1, $add, $n2, $eq, $result) {
    $_->pack(-side=>"left", -fill=>"both");
}

MainLoop();

# =================================================================

# an event handler
sub do_it {
    my $sum = $n1->get() + $n2->get();
    $result->configure(-text=>$sum);
}