From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Stefan Monnier via Users list for the GNU Emacs text editor Newsgroups: gmane.emacs.help Subject: Re: Generic functions: Specializers like `or' or `memq'? Date: Wed, 03 Nov 2021 21:31:50 -0400 Message-ID: References: <87r1bxcg6g.fsf@web.de> <87y265aymg.fsf@posteo.net> <87ilx9hrn6.fsf@web.de> <87a6ilorh0.fsf@ericabrahamsen.net> Reply-To: Stefan Monnier Mime-Version: 1.0 Content-Type: text/plain Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="12206"; mail-complaints-to="usenet@ciao.gmane.io" User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.0.50 (gnu/linux) To: help-gnu-emacs@gnu.org Cancel-Lock: sha1:mazhmU+gOL8hvQOdorFuqjYklcw= Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org Thu Nov 04 02:32:28 2021 Return-path: Envelope-to: geh-help-gnu-emacs@m.gmane-mx.org Original-Received: from lists.gnu.org ([209.51.188.17]) by ciao.gmane.io with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1miRcB-0002td-6u for geh-help-gnu-emacs@m.gmane-mx.org; Thu, 04 Nov 2021 02:32:27 +0100 Original-Received: from localhost ([::1]:55982 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1miRc9-0008Q9-Sj for geh-help-gnu-emacs@m.gmane-mx.org; Wed, 03 Nov 2021 21:32:25 -0400 Original-Received: from eggs.gnu.org ([2001:470:142:3::10]:40892) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1miRbo-0008Py-Li for help-gnu-emacs@gnu.org; Wed, 03 Nov 2021 21:32:04 -0400 Original-Received: from ciao.gmane.io ([116.202.254.214]:35258) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1miRbm-0005cK-Tc for help-gnu-emacs@gnu.org; Wed, 03 Nov 2021 21:32:04 -0400 Original-Received: from list by ciao.gmane.io with local (Exim 4.92) (envelope-from ) id 1miRbk-0002Gg-Ap for help-gnu-emacs@gnu.org; Thu, 04 Nov 2021 02:32:00 +0100 X-Injected-Via-Gmane: http://gmane.org/ Received-SPF: pass client-ip=116.202.254.214; envelope-from=geh-help-gnu-emacs@m.gmane-mx.org; helo=ciao.gmane.io X-Spam_score_int: -16 X-Spam_score: -1.7 X-Spam_bar: - X-Spam_report: (-1.7 / 5.0 requ) BAYES_00=-1.9, HEADER_FROM_DIFFERENT_DOMAINS=0.249, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: help-gnu-emacs@gnu.org X-Mailman-Version: 2.1.29 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-mx.org@gnu.org Original-Sender: "help-gnu-emacs" Xref: news.gmane.io gmane.emacs.help:134349 Archived-At: >>> I haven't tried it myself, but it seems like you would have to use >>> cl-generic-generalizers (see cl-generic.el) to do so. >> Yes, it should be doable. I find it a bit suspicious that this is not >> already available. > My understanding is that these more computationally-intensive > generalizers have the potential to seriously slow down method funcalls, > and so we're sort of gently discouraged from doing that. Not really, actually, no. The main problem is one of ordering between different methods when several methods are applicable. [ `cl-generic.el` solves this problem by forcing the generalizer to come with a priority (a number), which makes the ordering "trivial" for `cl-generic.el` but it can be hard to choose the right priority to use when defining a new specializer/generalizer. ] > Is anyone else's brain incapable of maintaining the distinction between > "specializer" and "generalizer"? A specializer is what you write in the `cl-defmethod`, it says this method is specialized for arguments of a particular type. It can be thought of as a type or a set of values. A generalizer is a sort of function that takes a value and returns the specializer to which it belongs (it "generalizes" from a value to a set that includes this value). Every kind of specializer comes with a matching generalizer as part of its implementation. This is not standard CLOS parlance, because CLOS does not include a mechanism to define new kinds of specializers: you can dispatch on (eql ) and you can dispatch on types and that's that (tho IIRC, you can actually extend it via the MOP, potentially with the help of some details of your Common-Lisp implementation). Stefan