[CM] Generalized rewrite pattern

[Rick Taube]

Hi torsten, i havent had time to play with the code yet -- is it doing 
somethig that the context free rules with the current rewrite pattern 
can't do?
ill look at the funcall problem tonight, ive got several other pattern 
things to fix...


On Wednesday, Feb 12, 2003, at 10:34 America/Chicago, Torsten Anders 
wrote:

> Hi,
>
> For my own purposes a wrote a somewhat generalized rewrite pattern.
> Perhaps somebody else is interested, so I send it in.
>
> Kind regards,
> Torsten
>
> Code:
> -----
>
> (defun mappend (func &rest inlists)
>   "Apply func to each element of inlist and append the result."
>   (apply #'append (apply #'mapcar func inlists)))
>
> (defun rewriter (fn)
>   "Defines a function for make-rewrite-fn for a context free rewrite.
> Only the rewrite function for a single stream item without its context
> need to be specified. The given function always needs to return a 
> list."
>   #'(lambda (vals)
>       (mappend fn vals)))
>
> (defmethod make-rewrite-fn ((init list) (fn function))
>   "Returns a function for a function item which recursively rewrites
> generations as specified by the given function."
>   (let ((curr init))
>     #'(lambda ()
> 	(let ((old curr))
> 	  (setf curr (funcall fn curr))
> 	  old))))
>
> #| ;; example:
>
> (next (new funcall
> 	   :of (make-rewrite-fn
> 		'(1)
> 		(rewriter
> 		 (let ((factor 1.3))
> 		   #'(lambda (x)
> 		       (cond ((< x (/ 1 factor))
> 			      (list (* x factor)))
> 			     ((>= x (/ 1 factor))
> 			      (list (/ x (expt factor 3))
> 				    (/ x (expt factor 5))))))))))
>       20)
> -> (1 0.4551662 0.26932913 0.59171605 0.35012785 0.76923084 0.4551662
> 0.35012788 0.20717627 0.59171605 0.45516622 0.26932913 0.76923084
> 0.59171605 0.35012785 0.35012788 0.20717627 0.76923084 0.4551662
> 0.45516622)
> |#
>
> ;; rewrite can be defined this way, if you want:
>
> (defmacro defrewriter-case (&rest clauses)
>   "Defines a function for make-rewrite-fn for a context free rewerite.
> Only case clauses need to be specified."
>   ;; just a demo to show a rewrite pattern can be defined this way
>   `(rewriter #'(lambda (val)
> 		 (case val
> 		   ,@clauses))))
>
> #| ;; example:
>
> (next (new funcall
> 	   :of (make-rewrite-fn '(b)
> 				(defrewriter-case
> 				  (a '(a b a))
> 				  (b '(b b a)))))
>       20)
> -> (B B B A B B A B B A A B A B B A B B A A)
> |#
>
>
> -- 
> Torsten Anders
> Sonic Arts Research Centre
> Queens University Belfast
> Tel: +44 28 9027 4831 (office)
>      +44 28 9066 7439 (private)
>
>
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