Cullen O'Neill wrote to me to remind me of Shriram Krishnamurthi's presentation titled The Swine Before Perl (PDF, PPT, audio). Krishnamurthi is a Schemer from Brown University who works on PLT Scheme. In his talk, Krishnamurthi uses the short example of a pattern matching automaton to show how Scheme (and by implication Lisp) macros can be used to develop custom-syntax for things like state machines. References to this talk have been posted a few times on comp.lang.lisp and it is very good. If you haven't done so already, I highly encourage you to download the presentation and go through it with the audio. The audio track is excellent and Krishnamurthi is a very entertaining speaker. I'm sure he's an excellent lecturing professor and his students must really enjoy every minute with him (well, except exam time, etc...).