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From: lgm@cbnewsc.ATT.COM (lawrence.g.mayka)
Newsgroups: comp.lang.scheme,comp.lang.lisp
Subject: Re: Correct LisP (was Re: in defense of C)
Message-ID: <14343@cbnewsc.ATT.COM>
Date: 13 Mar 90 14:05:37 GMT
References: <12572711825024@AIDA.CSD.UU.SE>
Reply-To: lgm@cbnewsc.ATT.COM (lawrence.g.mayka,ihp,)
Organization: AT&T Bell Laboratories
Lines: 32

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). 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.

Your argument is conceptually appealing, and well describes my own
programming practice:  I use FIRST and REST for the ubiquitous
list, and reserve CAR and CDR for intentional dotted pairs (such
as the constituents of an association list).  Formally, however, I
must quote "Common Lisp: the Language - Second Edition":

	p. 415:  "FIRST is the same as CAR, SECOND is the same
			as CADR..."

	p. 416:  "REST means the same as CDR but mnemonically
			complements FIRST."

Apparently the connection between dotted pairs and lists is deeply
ingrained into Common Lisp.


	Lawrence G. Mayka
	AT&T Bell Laboratories
	lgm@ihlpf.att.com

Standard disclaimer.