From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!not-for-mail From: pjb@informatimago.com (Pascal J. Bourguignon) Newsgroups: gmane.emacs.help Subject: Re: Element-Relative Sequence Insertion Date: Thu, 11 Jun 2009 16:36:25 +0200 Organization: Anevia SAS Message-ID: <7chbym25xy.fsf@pbourguignon.anevia.com> References: <7czlcf0wu9.fsf@pbourguignon.informatimago.com> <5f86d760-77b2-4ac0-897b-4eb8deca43fe@a36g2000yqc.googlegroups.com> <7cski62ach.fsf@pbourguignon.informatimago.com> NNTP-Posting-Host: lo.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8bit X-Trace: ger.gmane.org 1244731349 2133 80.91.229.12 (11 Jun 2009 14:42:29 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Thu, 11 Jun 2009 14:42:29 +0000 (UTC) To: help-gnu-emacs@gnu.org Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org Thu Jun 11 16:42:27 2009 Return-path: Envelope-to: geh-help-gnu-emacs@m.gmane.org Original-Received: from lists.gnu.org ([199.232.76.165]) by lo.gmane.org with esmtp (Exim 4.50) id 1MElTy-00031c-R2 for geh-help-gnu-emacs@m.gmane.org; Thu, 11 Jun 2009 16:42:23 +0200 Original-Received: from localhost ([127.0.0.1]:56615 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1MElTy-0005ax-7o for geh-help-gnu-emacs@m.gmane.org; Thu, 11 Jun 2009 10:42:22 -0400 Original-Path: news.stanford.edu!newsfeed.stanford.edu!news.tele.dk!news.tele.dk!small.news.tele.dk!proxad.net!feeder1-2.proxad.net!212.27.60.64.MISMATCH!cleanfeed3-b.proxad.net!nnrp9-1.free.fr!not-for-mail Original-Newsgroups: gnu.emacs.help Face: iVBORw0KGgoAAAANSUhEUgAAADAAAAAwAQMAAABtzGvEAAAABlBMVEUAAAD///+l2Z/dAAAA oElEQVR4nK3OsRHCMAwF0O8YQufUNIQRGIAja9CxSA55AxZgFO4coMgYrEDDQZWPIlNAjwq9 033pbOBPtbXuB6PKNBn5gZkhGa86Z4x2wE67O+06WxGD/HCOGR0deY3f9Ijwwt7rNGNf6Oac l/GuZTF1wFGKiYYHKSFAkjIo1b6sCYS1sVmFhhhahKQssRjRT90ITWUk6vvK3RsPGs+M1RuR mV+hO/VvFAAAAABJRU5ErkJggg== X-Accept-Language: fr, es, en X-Disabled: X-No-Archive: no User-Agent: Gnus/5.101 (Gnus v5.10.10) Emacs/22.2 (gnu/linux) Cancel-Lock: sha1:Y2VhNTY0YTU5NWQxYjY0Mzk4NGM5YzliYWM3Njk1M2M1ZTUwMmUyNw== Original-Lines: 75 Original-NNTP-Posting-Date: 11 Jun 2009 16:36:25 MEST Original-NNTP-Posting-Host: 88.170.236.224 Original-X-Trace: 1244730985 news-1.free.fr 5241 88.170.236.224:33579 Original-X-Complaints-To: abuse@proxad.net Original-Xref: news.stanford.edu gnu.emacs.help:169945 X-BeenThere: help-gnu-emacs@gnu.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Users list for the GNU Emacs text editor List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Original-Sender: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org Errors-To: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org Xref: news.gmane.org gmane.emacs.help:65172 Archived-At: Marc Tfardy writes: > Pascal J. Bourguignon schrieb: >> Nordlöw writes: >> >>> On 11 Juni, 14:38, p...@informatimago.com (Pascal J. Bourguignon) >>> wrote: >>>> Nordlöw writes: >>>>> How do I insert an element (object) relative to another in a sequence >>>>> (or list in my case)? Example: >>>>> (insert-after 'X '(a b c) 'b) => '(a b X c) >>>>> (insert-before 'X '(a b c) b) => '(a X b c) >>>> This is not what you want. You don't what these function to return a >>>> 2-element lists, the first of which is the symbol quote. Unless >>>> you're doing meta-programming you never want to have such a result. >>>> >>>> You wan this: >>>> >>>> (insert-after 'X '(a b c) 'b) --> (a b X c) >>>> (insert-before 'X '(a b c) 'b) --> (a X b c) >>>> >>>> Also, you may want to mention whether your insert-after and >>>> insert-before function are destructive or non-destructive. Since you >>>> show as only specification examples using literal data, we will assume >>>> you want them to be non-destructive. >>>> >>>> So you do that, just by doing it. There's nothing simplier. >>>> >>>> (defun insert-after (new list old) >>>> (cond ((null list) '()) >>>> ((eql old (car list)) (cons (car list) (cons new (cdr list)))) >>>> (t (cons (car list) (insert-after new (cdr list) old))))) >>>> >>>> (defun insert-before (new list old) >>>> (cond ((null list) '()) >>>> ((eql old (car list)) (cons new list)) >>>> (t (cons (car list) (insert-before new (cdr list) old))))) >>>> >>>> -- >>>> __Pascal Bourguignon__ >>> But how do I implement insert-after() and insert-before()? I guess the >>> code in the end doesn't do anything meaningful :) >> >> It does, but you have to decrypt it first. > > (defun insert-after (elt lst new) > (cond ((null lst) > '()) > ((eq new (car lst)) > (cons (car lst) (cons elt (cdr lst)))) > (t > (cons (car lst) (insert-after elt (cdr lst) new))))) > > (defun insert-before (elt lst new) > (cond ((null lst) > '()) > ((eq new (car lst)) > (cons elt lst)) > (t > (cons (car lst) (insert-before elt (cdr lst) new))))) > > What is the price? ;-) What's the point in renaming the parameters and introducing bugs? Check again the order of the parameters! Notice that (eq 3.141592 3.141592) --> nil ; which is the reason why eql should be used by default. And bad points for not being able to use rot13. You lose. :-) -- __Pascal Bourguignon__