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From: yonezawa@cs.uiuc.edu (Noritake Yonezawa)
Newsgroups: comp.lang.lisp
Subject: Re: novice question
Message-ID: <YONEZAWA.90Oct13095846@m.m.cs.uiuc.edu>
Date: 13 Oct 90 14:58:46 GMT
References: <90285.160549JEFHC@CUNYVM.BITNET> <3315@idunno.Princeton.EDU>
Sender: news@ux1.cso.uiuc.edu (News)
Organization: University of Illinois at Urbana-Champaign
Lines: 27
In-Reply-To: eliot@phoenix.Princeton.EDU's message of 13 Oct 90 04:05:04 GMT

In article <3315@idunno.Princeton.EDU> eliot@phoenix.Princeton.EDU (Eliot Handelman) writes:

> Try this, which slightly generalizes the trick of consing up the
> reversed list in an accumulator:
> 
> (defun mirror (list)
>   (labels ((mirror-1 (list accumulator)
> 	       (cond ((endp list) accumulator)
> 		     ((atom (car list))
> 		      (mirror-1 (cdr list)
> 				(cons (car list) accumulator)))
> 		     (t (mirror-1 (cdr list)
> 				  (cons (mirror-1 (car list) nil)
> 					accumulator))))))
>     (mirror-1 list nil)))

How about this?

(defun mirror (x) 
  (if (atom x)
      x
      (reverse (mapcar #'mirror x))))

--
Noritake Yonezawa [yonezawa@cs.uiuc.edu]
Department of Computer Science
University of Illinois at Urbana-Champaign