use strict;
use Tk;

my $phi = 0;
my $thisX = 185;
my $thisY = 500;
my $nextX = 185;
my $nextY = 500;

my $mw = MainWindow->new;
$mw->geometry( "700x700" );
my $c1 = $mw->Canvas( -background => 'black',
                      -height => 700,
                      -width => 700)
  ->pack;

use constant PRINT => 'P';
use constant LEFT  => '<';
use constant RIGHT => '>';

my $ax = "P>" x 4 . "P";
$ax =~ s/P/P<P>P>P<P/g for 1 .. 4;

for (split //, $ax)
  {
    if ($_ eq RIGHT)
      {
        # rotate right
        $phi += 90;
        $phi -= 360 if $phi >= 360;
      }

    elsif ($_ eq LEFT)
      {
        # rotate left
        $phi -= 90;
        $phi += 360 if $phi < 0;
      }

    elsif ($_  eq PRINT)
      {
        # print
        $thisX = $nextX;
        $thisY = $nextY;

        if    ($phi ==   0) { $nextX += 4 }
        elsif ($phi ==  90) { $nextY -= 4 }
        elsif ($phi == 180) { $nextX -= 4 }
        elsif ($phi == 270) { $nextY += 4 }

        $c1->createLine( $thisX, $thisY, $nextX, $nextY,
                         -fill => 'white' );

        $mw->update;
      }
  }

$c1->createText( 350, 350,
                 -text => "P E R L  \n           M O N K S",
                 -fill => 'white',
                 -width => 300);

MainLoop;

##</code><code>##

__SIG__
printf "You are here %08x\n", unpack "L!", unpack "P4", pack
  "L!", B::svref_2object(sub{})->OUTSIDE;