From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!not-for-mail From: "Pascal J. Bourguignon" Newsgroups: gmane.emacs.help Subject: Re: no empty (zero) string predicate in Elisp Date: Sun, 26 Apr 2015 06:06:48 +0200 Organization: Informatimago Message-ID: <87wq0zild3.fsf@kuiper.lan.informatimago.com> References: <87h9s4rhx5.fsf@debian.uxu> <874mo4jmb7.fsf@kuiper.lan.informatimago.com> NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit X-Trace: ger.gmane.org 1430022021 16968 80.91.229.3 (26 Apr 2015 04:20:21 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Sun, 26 Apr 2015 04:20:21 +0000 (UTC) To: help-gnu-emacs@gnu.org Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org Sun Apr 26 06:20:17 2015 Return-path: Envelope-to: geh-help-gnu-emacs@m.gmane.org Original-Received: from lists.gnu.org ([208.118.235.17]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1YmE3E-0001R6-Vz for geh-help-gnu-emacs@m.gmane.org; Sun, 26 Apr 2015 06:20:17 +0200 Original-Received: from localhost ([::1]:49857 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YmE3E-0002ld-3a for geh-help-gnu-emacs@m.gmane.org; Sun, 26 Apr 2015 00:20:16 -0400 Original-Path: usenet.stanford.edu!fu-berlin.de!uni-berlin.de!individual.net!not-for-mail Original-Newsgroups: gnu.emacs.help Original-Lines: 41 Original-X-Trace: individual.net a5ufDzHwbmSTVBvTwYl39A4ot8BuGXCEBrxzPOmiDcxfkSxOjr Cancel-Lock: sha1:ZjljNjJlMjU5YWZmODJlMzY4YzIxMDYwY2VlN2M5MmQ1ZWY1ZDYzYw== sha1:hfRWD/zzvWBOyRZ4QfDkP7IFZDM= Face: iVBORw0KGgoAAAANSUhEUgAAADAAAAAwAQMAAABtzGvEAAAABlBMVEUAAAD///+l2Z/dAAAA oElEQVR4nK3OsRHCMAwF0O8YQufUNIQRGIAja9CxSA55AxZgFO4coMgYrEDDQZWPIlNAjwq9 033pbOBPtbXuB6PKNBn5gZkhGa86Z4x2wE67O+06WxGD/HCOGR0deY3f9Ijwwt7rNGNf6Oac l/GuZTF1wFGKiYYHKSFAkjIo1b6sCYS1sVmFhhhahKQssRjRT90ITWUk6vvK3RsPGs+M1RuR mV+hO/VvFAAAAABJRU5ErkJggg== X-Accept-Language: fr, es, en User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3 (gnu/linux) Original-Xref: usenet.stanford.edu gnu.emacs.help:211717 X-BeenThere: help-gnu-emacs@gnu.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: Users list for the GNU Emacs text editor List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org Original-Sender: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org Xref: news.gmane.org gmane.emacs.help:103999 Archived-At: Stefan Monnier writes: >> Both for fundamental reasons, cardinals are built from a zero and a >> successor relationship, therefore a predicate for zero is not stupid, >> and a 1+ function neither; > > I know that you can model natural numbers from 0 and successor, but > Elisp integers have very little to do with it and are not encoded in > this way, and there isn't much code around that looks at them this way. > So, as much as I like this way to look at the world, I don't find it > helpful for Elisp. This is exactly what I'm pointing to! If you want to consider how elisp intgers are encoded on the native machine, then you definitely want a zerop function, because there are BEQ and SEQ instructions. >> and for optimization reasons on simplistic >> compilers: the hardware usually HAS specific (and optimized) >> instructions to test for zero and another to increment. > > C-h f zerop RET says: > > zerop is a compiled Lisp function in `subr.el'. > [...] > This function has a compiler macro `zerop--anon-cmacro'. > > and if you look at this mysterious zerop--anon-cmacro, you'll see that > it optimizes `zerop' by rewriting it to (= 0 ...), which is implemented > more efficiently. Not in emacs-version "24.3.1" where I produced the disassembly provided. But I'm happy to see it being optimized, this is one more reason to keep it and use it. -- __Pascal Bourguignon__ http://www.informatimago.com/ “The factory of the future will have only two employees, a man and a dog. The man will be there to feed the dog. The dog will be there to keep the man from touching the equipment.” -- Carl Bass CEO Autodesk