From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!not-for-mail From: Bill Atkins Newsgroups: gmane.emacs.devel Subject: Re: Documentation for car and cdr Date: Wed, 25 Jan 2006 18:19:29 -0500 Message-ID: <66b7e34b0601251519q3bf39198w707de60fe4ab5a09@mail.gmail.com> References: <66b7e34b0601251343i254e84c3o4b1bd882f01e2935@mail.gmail.com> NNTP-Posting-Host: main.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable X-Trace: sea.gmane.org 1138231361 14465 80.91.229.2 (25 Jan 2006 23:22:41 GMT) X-Complaints-To: usenet@sea.gmane.org NNTP-Posting-Date: Wed, 25 Jan 2006 23:22:41 +0000 (UTC) Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Thu Jan 26 00:22:33 2006 Return-path: Envelope-to: ged-emacs-devel@m.gmane.org Original-Received: from lists.gnu.org ([199.232.76.165]) by ciao.gmane.org with esmtp (Exim 4.43) id 1F1ty1-0005uA-AV for ged-emacs-devel@m.gmane.org; Thu, 26 Jan 2006 00:22:21 +0100 Original-Received: from localhost ([127.0.0.1] helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1F1u0m-0003tt-J1 for ged-emacs-devel@m.gmane.org; Wed, 25 Jan 2006 18:25:12 -0500 Original-Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1F1ty7-0000sV-Ng for emacs-devel@gnu.org; Wed, 25 Jan 2006 18:22:27 -0500 Original-Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1F1ty5-0000qU-0q for emacs-devel@gnu.org; Wed, 25 Jan 2006 18:22:26 -0500 Original-Received: from [199.232.76.173] (helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1F1ty1-0000pw-Os for emacs-devel@gnu.org; Wed, 25 Jan 2006 18:22:23 -0500 Original-Received: from [64.233.184.200] (helo=wproxy.gmail.com) by monty-python.gnu.org with esmtp (Exim 4.52) id 1F1tvU-0005xq-N2 for emacs-devel@gnu.org; Wed, 25 Jan 2006 18:19:44 -0500 Original-Received: by wproxy.gmail.com with SMTP id i30so224470wra for ; Wed, 25 Jan 2006 15:19:29 -0800 (PST) DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=beta; d=gmail.com; h=received:message-id:date:from:sender:to:subject:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:references; b=F0jxT5yy1AzP7EQKe5Lpa46T45zxjFgYvY2FmEcgTHIXNSISJdnrKtxFOxdKWYgmQ5eY/317lRZvt72nNcFwQebn5F7zf59xjsVpjF1VDpXpjGi1o8DNUNM6QIIeZ6xOF6Hz9rFzd6TzBgFYUwDk6/TrWhQyOGiTfte+hyiBq9g= Original-Received: by 10.65.150.10 with SMTP id c10mr869038qbo; Wed, 25 Jan 2006 15:19:29 -0800 (PST) Original-Received: by 10.65.176.8 with HTTP; Wed, 25 Jan 2006 15:19:29 -0800 (PST) Original-To: emacs-devel@gnu.org In-Reply-To: Content-Disposition: inline X-BeenThere: emacs-devel@gnu.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: "Emacs development discussions." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Original-Sender: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Errors-To: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Xref: news.gmane.org gmane.emacs.devel:49546 Archived-At: On 1/25/06, Alan Mackenzie wrote: > >Why do we need to "speak loosely"? > > So as to be immediately understandable. > > >Including a link to a description of cons cells is completely adequate. > > Yes, but only in addition to an intuitively meaningful description, not > instead of it. Because that would force the poor hacker to go and look > somewhere else. Having to go and look somewhere else is always a pain in > the posterior, particularly when a one-liner explanation is all that is > sought. If you're writing Elisp code, and you need to go to the documentation for CAR and CDR, you're probably better off reading an introduction to Lisp (or following a link to an explanation of cons cells). > >Your definitions are misleading in any case. CAR and CDR do not > >necessarily deal with lists; > > It is merely that the parameter to cdr is called LIST. I haven't > otherwise implied that it must be a list. For example "(a . b)" without > it's first element is "b", or something like it. > > >as others have pointed out, a cons is a distinct data structure that is > >used to compose lists only by convention. These are not "abstract > >concepts," they're simply how Lisp works. > > We're reduced to silly semantic arguments about "abstract" now. Others > have asserted that "cdr returns the cdr" is a coherent description of > cdr. They are thus implying that "cdr" is semantically different from > "cdr", otherwise that description would be circular and vacuous. I > disagree with them, and used the term "abstract concept" only to try to > highlight what to me is an absurdity. A car is the first element of a cons; a cdr is the second. That's pretty concrete. > >-- > >Bill Atkins > > -- > Alan Mackenzie (Munich, Germany) > > > -- Bill Atkins