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Message from discussion Trying to make my own reverse function
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Nils M Holm  
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 More options Sep 25 2012, 1:08 pm
Newsgroups: comp.lang.lisp
From: Nils M Holm <news2...@t3x.org>
Date: 25 Sep 2012 17:08:47 GMT
Local: Tues, Sep 25 2012 1:08 pm
Subject: Re: Trying to make my own reverse function
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Yves S. Garret <yoursurrogate...@gmail.com> wrote:

> ================================================
> (defun custom-reverse(list-to-reverse)
>   (if (equal (cdr list-to-reverse) nil)
>       (car list-to-reverse)
>       (cons (custom-reverse (cdr list-to-reverse))
>             (cons (car list-to-reverse) nil))))
> ================================================

> Now, it doesn't work.  At least not very well.  The problem is
> what should I return from the method?  Also, and I could be wrong,
> but is it possible to make a reverse method using car, cdr and cons?

Okay, here are a few hints.

- How do you reverse an empty list?

- How do you reverse a non-empty list?

- Fill in the missing parts:

  (DEFUN R (L)
    (IF (NULL L)
        reverse-empty-list
        reverse-non-empty-list))

- You will get extra points for not using APPEND.

BTW:

- (EQUAL X NIL)  equals  (NULL X)

- (CONS X NIL)   equals  (LIST X)

--
Nils M Holm  < n m h @ t 3 x . o r g >  www.t3x.org


 
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