tron.icn: Program to play a Tron-like video game

Rules: You're yellow, and you leave a yellow trail when you walk.
You never stop until you die. You die when you hit something
yellow. Use the arrow keys to change your direction. Try to make
the best score you can before you die. You only live once.

In the beginning it's a black arena with yellow walls and a red
3x3 pixel square somewhere. Walking over a red pixel gives you
one point and makes another 3x3 square appear somewhere.  So,
crossing a 3x3 red square from one side to another gives you
three points and makes three other squares appear in random
positions.

Walking over black pixels is harmless.

Sometimes the red squares will appear over your trail. Then some
pixels of your trail will become red and you'll be able to cross.

The game loop and the outer loop: typing "Q" or Esc or losing when
you're playing makes you go to the outer loop; in the outer loop
typing "P" or Enter or space restarts the game, and typing "Q" or
Esc leaves the program.

Source:     <http://angg.twu.net/ICON/tron.icn>
Htmlized:   <http://angg.twu.net/ICON/tron.icn.html>
Screenshot: <http://angg.twu.net/ICON/tron.icn.png>
See also:   <http://angg.twu.net/elisp/tron.el.html>
            <http://angg.twu.net/elisp/tron.el.png>