This is Melanie Mitchell's Copycat. It uses the Flavors object-oriented extension that originated in Lisp Machine Lisp, so as originally distributed, it was not portable Common Lisp code. (There are, I gather, at least two commercial CL implementations that support Flavors, but AFAIK none of the open-source ones have it.) I have made it run in Common Lisp, however, by reimplementing, on top of CLOS, the requisite Flavors functionality (see src/defs.lisp). It's certainly not a full Flavors implementation, nor is it particularly optimized, but it's enough to run Copycat.

The graphics code was written to work with Lucid CL. I have not attempted to port it to something else, or indeed, even looked into how to do that. I am just running Copycat from the REPL. If anyone wants to get the graphics working, I would be happy to merge your PR.

The original Copycat distribution can be found on Melanie Mitchell's site. I don't see anything that looks like a license in this distribution, so I tentatively conclude that her intent was to place the code in the public domain.

All I have done to this code is:

• Rename the files from .l to .lisp
• Reorganize them into src/ and src/graphics/ subdirectories
• Delete trailing whitespace
• Define a copycat: package (which shadows defmethod) and put all the files in it
• Add the minimal Flavors implementation, and get the code to build cleanly with it (in some cases this required moving a defflavor form to earlier in the build; see src/defflavors.lisp)
• Make it ASDF-loadable (the code in src/graphics/ is not currently built)
• Add :verbose and :slighly-verbose arguments to init-ccat

I've added a few comments, marked with [SLB].

To run, just put it in quicklisp/local-projects/ or wherever you put such things (or maybe it will be in Quicklisp by the time you read this), do (ql:quickload "copycat"), and then:

> (in-package :copycat)
> (init-ccat "abc" "abd" "ijk")

Tested only on SBCL so far, but I'll be pretty surprised if there are any portability issues. (Do report them, of course, if you run into them.)

You may also be interested in these Copycat reimplementations:

• One in Python by J. Alan Brogan
• Another one in Python by Lucas Saldyt
• A Java port by "speakeasy"
• A JavaScript port by "Paul-G2"; you can run it in your browser by going here (recommended)