I recommend that you use cl-yacc by Juliusz Chroboczek instead of this package. Among other things, his package properly supports operator precedence and so on, and is a lot more polished -- I bet it's way faster, too. If that's the case, why am I releasing this code? Well, I had already written some things (like m68k-assembler) that depend on it. Also, the code is much shorter and I feel it might be more understandable to someone unfamiliar with either package and looking to modify a parser generator. Also, the default mode of operation for this package is to write the tables and parser to a stream, so you don't need to have this package around at runtime. Look at tests.lisp (or m68k-grammar.lisp in the m68k-assembler package) for examples of the grammar form.