SCHEME CODE FOR PATTERN MATCHING
                                       
   Here's some Scheme code to do pattern matching.
     * Andrew Wright's pattern matching system (match.tar.gz).
     * Christian Queinnec's pattern-match compiler code for compiling
       non-linear, second-order patterns on S-Expressions
       (matchcomp.tar.gz).
     * A pattern matcher from chapter 15 of Programming in MacScheme, by
       Eisenberg, Hartheimer, Clinger, Abelson (patmat.scm).