#!/usr/bin/perl 

use strict;
use warnings;
use Tk;
use Tk::Pane;

my $mw = MainWindow->new();
$mw->geometry("100x100");
$mw->Button( -text => "START", -command => \&start_computation )->pack;

MainLoop;

sub start_computation {
    my $progress = $mw->Toplevel();
    $progress->geometry("100x100");
    my $pane = $progress->Scrolled(
        'Pane',
        -scrollbars => 'soe',
        -sticky     => 'we',
        -gridded    => 'y'
    )->pack( -fill => 'both', -expand => 1 );
    my $text = "Computation started...\n";
    $pane->Frame;
    my $label =
      $pane->Label( -text => $text )->pack( -side => 'left', -fill => 'x' );

    # doing several computation steps
    foreach my $step ( 1 .. 10 ) {
        sleep(1);
        $text .= "Step $step finished.\n";
        $label->destroy;
        $label = $pane->Label( -text => $text )->pack( -side => 'left' );
        $pane->update;
    }

    $text .= "\nComputation finished.\n";
    $label->destroy;
    $label = $pane->Label( -text => $text )->pack( -side => 'left' );
    $pane->update;

    $pane->Button( -text => "QUIT", -command => sub { exit; } )->pack;
}