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From: moore%cdr.utah.edu@cs.utah.edu (Tim Moore)
Newsgroups: comp.lang.lisp,comp.lang.scheme
Subject: Re: Correct LisP (was Re: in defense of C)
Message-ID: <1990Mar12.104518.1412@hellgate.utah.edu>
Date: 12 Mar 90 17:45:18 GMT
References: <1942@skye.ed.ac.uk> <14236@cbnewsc.ATT.COM> <12572711825024@AIDA.CSD.UU.SE>
Organization: University of Utah CS Dept
Lines: 29

In article <12572711825024@AIDA.CSD.UU.SE> D89.JOHNNY-BILLQUIST@AIDA.CSD.UU.SE (Johnny Billquist) writes:
>In article <14112@cbnewsc.ATT.COM> lgm@cbnewsc.ATT.COM (lawrence.g.mayka,ihp,) writes:
>The correct argument to CAR and CDR is *not* lists, but
>s-expr (punctuated pairs to be specific). The fact that most
>(if not all) LisPs implement lists by punctuated pairs
>is a feature you should not rely upon. 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? If you should do it *really* right,
>CAR and CDR should not be able to work on lists at all,
>however convenient it might be.
>
>Anybody who cares to flame can do it to me personally.

I don't know what Lisps you're refering to, but Common Lisp isn't one
of them. The argument to CAR and CDR is LISTP, which means its either
a cons pair or NIL. How could lists be implemented in some other way?
If some sort of cdr-coding trick or array scheme is used internally in the
implementation, CAR and CDR better still work, or the implementation
is quite broken.

FIRST and REST are for quiche eaters :-) Or, with only have a smiley,
for non-Lisp programmers who are slumming.

>D89.JOHNNY-BILLQUIST@AIDA.CSD.UU.SE

Tim Moore                     moore@cs.utah.edu {bellcore,hplabs}!utah-cs!moore
"Ah, youth. Ah, statute of limitations."
		-John Waters