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From: raja@copper.ucs.indiana.edu (Raja Sooriamurthi)
Newsgroups: comp.lang.lisp
Subject: Re: Mirror speeds
Message-ID: <raja.655852887@copper>
Date: 13 Oct 90 21:21:27 GMT
References: <47064@cornell.UUCP>
Sender: news@iuvax.cs.indiana.edu
Distribution: comp
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wilk@fife.cs.cornell.edu (Michael Wilk) writes:

> Here are some timing results on suggested solutions for the "mirror"
> function: I won't reveal the huge list I tried this on, but trust me:
> It was big.

[stats. deleted]


Here is a CPSed form of the mirror function. Now all calls to the
auxillary function mir are properly tail recursive and a scheme
implementation (and some CL implementations) would optimize the
recursive calls into jumps.

Just out of curiosity I'd like to see how this version compares with
the other ones. The code below is in Scheme where in I've used scheme's
equivalent of the Y combinator, rec,  to define mir. Could you convert this
into Common Lisp and run it on your data set.

- Raja
raja@cs.indiana.edu

(define mirror/k
  (lambda (l)
    ((rec mir
	  (lambda (l k)
	    (cond
	     [(atom? l) (k l)]
	     [else 
	      (mir (car l)
		   (lambda (a)
		     (mir (cdr l)
			  (lambda (d) (k (append d (list a)))))))])))
     l (lambda (v) v))))