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Re: replacing a certain element in a list with another


From: Klaus Berndl
Subject: Re: replacing a certain element in a list with another
Date: 30 Sep 2003 11:59:39 +0200
User-agent: Gnus/5.09 (Gnus v5.9.0) Emacs/21.3

On 30 Sep 2003, David Kastrup wrote:

>  Klaus Berndl <address@hidden> writes:
>  
> > Suppose i have the following list:
> > 
> > '(a b c d)
> > 
> > What is a good way to replace one of the list-elements with another, so
> > foe example replacing the 'c with 'e?
>  
> > But: i do not want using any c-functions, so i would prefer a
> > solution without using `substitute'!
>  
>  Uh, what?

This comes from a recommendation in the elisp-info-manual (Standards -->
Coding conventions"):

   * Please don't require the `cl' package of Common Lisp extensions at
     run time.  Use of this package is optional, and it is not part of
     the standard Emacs namespace.  If your package loads `cl' at run
     time, that could cause name clashes for users who don't use that
     package.

     However, there is no problem with using the `cl' package at compile
     time, for the sake of macros.  You do that like this:

          (eval-when-compile (require 'cl))

I interpret this ("...for the sake of macros...") so, that at least for
packages for GNU Emacs the code can use cl-macros but should not use any
functions from the cl package. Please correct me if i have misunderstood here
something!?

>  
>  Anyhow, try
>  
>  (let ((xxx '(a b c d)))
>     (setcar (member 'c xxx) 'e)
>     xxx)

Thanks a lot, David!

Ciao,
Klaus

-- 
Klaus Berndl                    mailto: address@hidden
sd&m AG                         http://www.sdm.de
software design & management    
Thomas-Dehler-Str. 27, 81737 M√ľnchen, Germany
Tel +49 89 63812-392, Fax -220


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