%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%  
%  FOUR.PS                     by John Earnest
%  
%  A compiler for a minimal subset of Forth,
%  along with an associated VM and visual debugger,
%  all implemented in PostScript.
%  
%  The 'prog' definition contains a string
%  which will be compiled and run on the FOUR.PS
%  platform. The following ANS Forth words are
%  available:
%  
%  : ; exit if else then begin until repeat
%  do loop +loop variable dup drop swap over
%  @ ! + - = > < i i' j >r r> not and or
%  
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

Just what it says on the packet. If you'd like to give this a spin, the easiest way is to install GhostScript (http://pages.cs.wisc.edu/~ghost/) and then launch the script interactively:

  >gs four.ps

You'll be given the option to advance the simulation one "tick" at a time by pressing return.

Otherwise, just open the file in the postscript viewer of your choice (including many PDF viewers) and be treated to a "flipbook" of the execution trace.

Four.PS is released under the WTFPL, so do whatever you like with this code. If you particularly enjoy Four.PS or make some spiffy additions I'd love to hear about it.

-----------------------------------------------------------------------

            DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE 
                    Version 2, December 2004 

 Copyright (C) 2004 Sam Hocevar <sam@hocevar.net> 

 Everyone is permitted to copy and distribute verbatim or modified 
 copies of this license document, and changing it is allowed as long 
 as the name is changed. 

            DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE 
   TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION 

  0. You just DO WHAT THE FUCK YOU WANT TO.