From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Eli Zaretskii Newsgroups: gmane.emacs.bugs Subject: bug#66756: 30.0.50; [PATCH] Improve discussion of 'let' in Elisp Introduction manual Date: Sat, 04 Nov 2023 10:27:51 +0200 Message-ID: <83fs1l6hyw.fsf@gnu.org> References: Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="21220"; mail-complaints-to="usenet@ciao.gmane.io" Cc: Jim Porter , 66756@debbugs.gnu.org To: Richard Stallman Original-X-From: bug-gnu-emacs-bounces+geb-bug-gnu-emacs=m.gmane-mx.org@gnu.org Sat Nov 04 09:28:48 2023 Return-path: Envelope-to: geb-bug-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 1qzC1O-0005IM-7t for geb-bug-gnu-emacs@m.gmane-mx.org; Sat, 04 Nov 2023 09:28:46 +0100 Original-Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1qzC15-0005gu-Ed; Sat, 04 Nov 2023 04:28:27 -0400 Original-Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qzC14-0005gm-Nj for bug-gnu-emacs@gnu.org; Sat, 04 Nov 2023 04:28:26 -0400 Original-Received: from debbugs.gnu.org ([2001:470:142:5::43]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1qzC14-0004ki-FN for bug-gnu-emacs@gnu.org; Sat, 04 Nov 2023 04:28:26 -0400 Original-Received: from Debian-debbugs by debbugs.gnu.org with local (Exim 4.84_2) (envelope-from ) id 1qzC1d-0007do-LE for bug-gnu-emacs@gnu.org; Sat, 04 Nov 2023 04:29:01 -0400 X-Loop: help-debbugs@gnu.org Resent-From: Eli Zaretskii Original-Sender: "Debbugs-submit" Resent-CC: bug-gnu-emacs@gnu.org Resent-Date: Sat, 04 Nov 2023 08:29:01 +0000 Resent-Message-ID: Resent-Sender: help-debbugs@gnu.org X-GNU-PR-Message: followup 66756 X-GNU-PR-Package: emacs X-GNU-PR-Keywords: patch Original-Received: via spool by 66756-submit@debbugs.gnu.org id=B66756.169908652229341 (code B ref 66756); Sat, 04 Nov 2023 08:29:01 +0000 Original-Received: (at 66756) by debbugs.gnu.org; 4 Nov 2023 08:28:42 +0000 Original-Received: from localhost ([127.0.0.1]:60489 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from ) id 1qzC1J-0007dA-O1 for submit@debbugs.gnu.org; Sat, 04 Nov 2023 04:28:42 -0400 Original-Received: from eggs.gnu.org ([2001:470:142:3::10]:58772) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from ) id 1qzC1I-0007cv-3I for 66756@debbugs.gnu.org; Sat, 04 Nov 2023 04:28:40 -0400 Original-Received: from fencepost.gnu.org ([2001:470:142:3::e]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qzC0c-0004hs-NO; Sat, 04 Nov 2023 04:27:58 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=gnu.org; s=fencepost-gnu-org; h=References:Subject:In-Reply-To:To:From:Date: mime-version; bh=PQIuBbTL7taVCJPMSHY6sljJE562Q9HEcQ4vn2MU6OA=; b=RbxIMFdg3b0B qNp8DqnUQpeFfykiOy5CyNVDEQ8ty63JvnEbDximA0KldyxJzmTVe8rC1tk0aRlxqh3JpgfSutGFL ZxCLEh2Xdyi5MjMep/JUUFpqTo8llvQyAY8WloXf4VfapUQkcITWVdJX4pGemuHnNipcyTyYcyEWl SSkP9qXbe53IaC93TD3LqNB13t8TfqrtklnvqMUTcs3XwOGeIAHhTQNyKiYFAvXD8+ZPU7VvVOFWk 76Exg9LkmfgGA8d/aMzdP5LsXh31/cDwbFf4PR8f+73Epdse2suUvvPo/F+MVU44DWNF2qliL1oFG qVBQtdavPgn2RTfH/6d7Mg==; In-Reply-To: (message from Jim Porter on Thu, 26 Oct 2023 11:30:46 -0700) X-BeenThere: debbugs-submit@debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list X-BeenThere: bug-gnu-emacs@gnu.org List-Id: "Bug reports for GNU Emacs, the Swiss army knife of text editors" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: bug-gnu-emacs-bounces+geb-bug-gnu-emacs=m.gmane-mx.org@gnu.org Original-Sender: bug-gnu-emacs-bounces+geb-bug-gnu-emacs=m.gmane-mx.org@gnu.org Xref: news.gmane.io gmane.emacs.bugs:273753 Archived-At: > Date: Thu, 26 Oct 2023 11:30:46 -0700 > From: Jim Porter > > On 10/26/2023 12:09 AM, Eli Zaretskii wrote: > > Thanks. > > > > The challenge in updating the Lisp Introduction manual is to try to > > keep its informal and reader-friendly style as much as possible. It > > is not just another ELisp Reference manual! So please try to keep > > that in mind when you write the text, and in particular try not to > > modify the existing text that is still accurate -- it was written by a > > master, and each word there counts, even if it looks at first sight as > > not important. > > Ok, here's a second attempt. I've tried to avoid changing anything that > I don't think is truly necessary. I did alter a bit of the original > wording to emphasize that under lexical binding, 'let' isn't about time, > but about place. For example, that's why I changed this: > > > This is like understanding that whenever your host refers to ``the house'', he means his house, not yours. > > to this: > > > This is like understanding that in your host's home, whenever he refers to ``the house'', he means his house, not yours. > > My previous concern about the "lexical binding" digression still applies > though. However, I'm not sure how to get around that at present; if we > want to talk about lexical binding in the manual, we need to get users > to enable it, so I think it's unavoidable that we at least mention it. I > tried to introduce the jargon as gently as I could (by first introducing > the term "binding" on its own before mentioning "lexical/dynamic > binding"), but it's still a bit intimidating. On the positive side, when > lexical binding is the default, we could remove that entire digression. > > There's also an argument that the example I added is in the wrong spot, > since we haven't actually introduced the 'let' syntax yet. However, I > personally find the example to be pretty useful since it shows off one > of the key differences between lexical and dynamic binding, and helps > show one of the boundaries of the 'let' form's scope. I myself tend to > learn best by seeing examples of that sort. Fixing the order so we > introduce the syntax first would require more extensive changes to this > section... Richard, could you please review these changes? > From 12847e0d59b2de3791efa090addc0169e713e6d1 Mon Sep 17 00:00:00 2001 > From: Jim Porter > Date: Wed, 25 Oct 2023 20:43:57 -0700 > Subject: [PATCH] Introduce 'let' using lexical binding in the Lisp > Introduction > > * doc/lispintro/emacs-lisp-intro.texi (Prevent confusion): Rework the > explanation to discuss how things work under lexical binding > (including how to enable it). > --- > doc/lispintro/emacs-lisp-intro.texi | 67 ++++++++++++++++++++++------- > 1 file changed, 51 insertions(+), 16 deletions(-) > > diff --git a/doc/lispintro/emacs-lisp-intro.texi b/doc/lispintro/emacs-lisp-intro.texi > index fce7583fe91..e805833f979 100644 > --- a/doc/lispintro/emacs-lisp-intro.texi > +++ b/doc/lispintro/emacs-lisp-intro.texi > @@ -3602,24 +3602,59 @@ Prevent confusion > @cindex @samp{variable, local}, defined > The @code{let} special form prevents confusion. @code{let} creates a > name for a @dfn{local variable} that overshadows any use of the same > -name outside the @code{let} expression. This is like understanding > -that whenever your host refers to ``the house'', he means his house, not > -yours. (Symbols used in argument lists work the same way. > +name outside the @code{let} expression (in computer science jargon, we > +call this ``binding'' the variable). This is like understanding that > +in your host's home, whenever he refers to ``the house'', he means his > +house, not yours. (Symbols used in argument lists work the same way. > @xref{defun, , The @code{defun} Macro}.) > > -Local variables created by a @code{let} expression retain their value > -@emph{only} within the @code{let} expression itself (and within > -expressions called within the @code{let} expression); the local > -variables have no effect outside the @code{let} expression. > - > -Another way to think about @code{let} is that it is like a @code{setq} > -that is temporary and local. The values set by @code{let} are > -automatically undone when the @code{let} is finished. The setting > -only affects expressions that are inside the bounds of the @code{let} > -expression. In computer science jargon, we would say the binding of > -a symbol is visible only in functions called in the @code{let} form; > -in Emacs Lisp, the default scoping is dynamic, not lexical. (The > -non-default lexical binding is not discussed in this manual.) > +@cindex lexical binding > +@cindex binding, lexical > +@cindex dynamic binding > +@cindex binding, dynamic > +Before we begin discussing @code{let} in detail, we must first mention > +an important note. For historical reasons, Emacs Lisp uses a form of > +variable binding called ``dynamic binding''. However, this manual > +will discuss the preferred form of binding, called ``lexical binding'' > +(if you have programmed in other languages before, you're likely > +already familiar with how lexical binding behaves). In order to use > +lexical binding, you should add something like this to the first line > +of your Emacs Lisp file: > + > +@example > +;;; -*- lexical-binding: t -*- > +@end example > + > +For more information about this, @pxref{Selecting Lisp Dialect, , , > +elisp, The Emacs Lisp Reference Manual}. > + > +With that out of the way, we can get back to discussing @code{let}. > +Another way to think about @code{let} is that it defines a place in > +your code where the variables you named have their own local meaning. > +Outside of the @code{let} body, they have another meaning (or they may > +not be defined at all). > + > +This means that inside the @code{let} body, calling @code{setq} > +for a variable named by the @code{let} expression will set the value > +of the @emph{local} variable of that name. This also means that > +outside of the @code{let} body, calling @code{setq} for a variable > +named by the @code{let} expression will @emph{not} affect that local > +variable. > + > +For example, if you call a function inside of a @code{let} > +body, that function's body would be unable to ``see'' (or modify) the > +value of a local variable from the @code{let} expression: > + > +@example > +(setq x 1) > + > +(defun getx () > + x) > + > +(let ((x 2)) > + (get-x)) > + @result{} 1 > +@end example > > @code{let} can create more than one variable at once. Also, > @code{let} gives each variable it creates an initial value, either a > -- > 2.25.1 >