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

my $size = 12;
my $main = new MainWindow();
$main->geometry('400x400+200+200');

my $font = $main->fontCreate(
          -size => $size,
          -weight => 'bold');

my $button;
$button = $main->Button(-text => "+",
           -font => $font,
           -command =>	sub{
                    $button->configure( -font=> $main->fontCreate(
                           -size => $size++,
                          -weight => 'bold')),
                      } );

$button->pack();

MainLoop;