Mark Johnson, mark@adler.philosophie.uni-stuttgart.de, just posted a LALR parser generator for Common Lisp to the USENET newsgroup comp.compilers. It looks like this should fit your needs. If you don't have access to this, send me mail and I'll forward it to you. He also mentions that he developed it as part of a natural language package he wrote a few years ago. Try contacting him regarding this stuff.