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Message from discussion Simple newbie list processing troubble
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Marco Antoniotti  
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 More options Sep 28 2002, 1:09 pm
Newsgroups: comp.lang.lisp
From: Marco Antoniotti <marc...@cs.nyu.edu>
Date: 28 Sep 2002 13:10:33 -0400
Local: Sat, Sep 28 2002 1:10 pm
Subject: Re: Simple newbie list processing troubble
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pyda...@ec.auckland.ac.nz (Peder Y) writes:
> Say I have a function foo that is supposed to take a list as input (A
> B C D...). The function will then traverse the list looking for an
> element, and change that element. That's basically it.

> For example, say, the function shall set all elements of lst to 'A:
> Why is this wrong?

> (defun foo (lst)
>   (loop for x in lst do
>              (setf (car x) 'A)))

The above will not necessarily work because you are changing the list
as you are traversing it.  This is specifically mentioned in the
language standard.

To do that kind of things you should look to the standard functions
SUBSTITUTE and NSUBSTITUTE.

Cheers

--
Marco Antoniotti ========================================================
NYU Courant Bioinformatics Group        tel. +1 - 212 - 998 3488
715 Broadway 10th Floor                 fax  +1 - 212 - 995 4122
New York, NY 10003, USA                 http://bioinformatics.cat.nyu.edu
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                           Bill Murray in `Ghostbusters'.


 
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