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From: jeff@aiai.ed.ac.uk (Jeff Dalton)
Newsgroups: comp.lang.scheme,comp.lang.lisp
Subject: Re: Correct LisP (was Re: in defense of C)
Message-ID: <2034@skye.ed.ac.uk>
Date: 14 Mar 90 15:17:13 GMT
References: <1942@skye.ed.ac.uk> <14236@cbnewsc.ATT.COM> <12572711825024@AIDA.CSD.UU.SE>
Reply-To: jeff@aiai.UUCP (Jeff Dalton)
Organization: AIAI, University of Edinburgh, Scotland
Lines: 23

In article <12572711825024@AIDA.CSD.UU.SE> D89.JOHNNY-BILLQUIST@AIDA.CSD.UU.SE (Johnny Billquist) writes:
>The correct argument to CAR and CDR is *not* lists, but
>s-expr (punctuated pairs to be specific). 

Ok so far.

>The fact that most (if not all) LisPs implement lists by
>punctuated pairs is a feature you should not rely upon.

Why not?  Indeed, in Lisp lists just are dotted pairs used
in a certain way.  You might argue that "list" ought to be
more abstract, but it isn't.

>That is why the functions FIRST and REST exists. Sure, they do just
>CAR and CDR, but what if you stumles upon a LisP which implement
>lists in another way? 

Most Lisps don't have FIRST and REST.

A CL or Scheme that implements lists some other way wouldn't be a
conforming implementation.

-- Jeff