Books of Note

Practical Common
LispThe best intro to start your journey. Excellent coverage of CLOS.

ANSI Common
LispAnother great starting point with a different focus.

Paradigms of Artificial Intelligence
ProgrammingA superb set of Lisp examples. Not just for the AI crowd.

Monday, June 28, 2004

Automaton cleanup 

One of the nice things about posting code into your blog is there are a wealth of people on the 'net that will keep you honest. After posting my automaton code yesterday, Tim Moore wrote me with a style tip. Basically, Tim suggested I clean up the CONS/APPEND nightmare that existed in the innermost LOOP form. I had been thinking the same thing the night before when I did the post, so the suggestion was spot on. In particular, Tim said that his own personal rule is that when he sees lots of CONS/APPEND/LIST action, he takes it as a sign to replace the mess with a backquoted form.

Without further delay...

(defmacro define-automaton (name states &key (stop 'stop) (debug nil))
  (let ((event-func (gensym "func")))
    `(defun ,name (,event-func)
	 ,@(loop for (state-name . transitions) in states
		 (list state-name
		       `(case (funcall ,event-func)
 			 ,@(loop for (match next . actions) in transitions
				 collecting `(,match
					      ,@(when debug
						      `((format t "Matched ~A. Transitioning to state ~A.~%" ',match ',next)))
					      (go ,next))))
		       `(go ,state-name)))

Ahhhh... much better.

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