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Re: [Axiom-developer] Lisp macro fun...

From: Waldek Hebisch
Subject: Re: [Axiom-developer] Lisp macro fun...
Date: Thu, 19 Apr 2007 13:55:41 +0200 (CEST)

> I have been attempting to generalize Waldek's finite state machine
> using macros, and have essentially run up against the limits of my tiny
> Lisp skills.  Can anybody tell me how to get this thing to expand into
> something like Waldek's code?  (I can provide the whole file if it is
> needed.)

I must admit that I do not understand what you are tring to do now
-- what you posted looks like macro definition, but it contains
(hardcodes) most of had written version.

Have you looked at <> (it
contains Scheme example of macro-generating finite state

Low level macro version of finite state machine may look like:

  (state normal-start
     (-> start-tag-code-1 chunk-start-tag-1)
     (-> newline-code normal-start)
     (default normal))
  (state normal
     (-> newline-code normal-start)
     (default normal))
  (state chunk-start-tag-1
     (-> start-tag-code-2 in-chunk-start-tag
         ;;; Action
         (setf start-pos (+ pos 1)))

To generate our  code from the above one has to define macros
automaton, state, defalut and ->.  state, defalut and -> may
be local to automaton.  In the above I assumend that we use
chacter codes, but we could also use characters and write:

   (-> #\< chunk-start-tag-1)

A higher level version may do transitions on strings, so you
could write:

   (-> "<<"  in-chunk-start-tag
         ;;; Action
         (setf start-pos (+ pos 1)))

and the macros would automatically generate intermediate states.

                              Waldek Hebisch

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