GNU bug report logs - #33550
[PATCH] mention let* in if-let

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Alex Branham <alex.branham <at> gmail.com>
To: bug-gnu-emacs <at> gnu.org
Subject: [PATCH] mention let* in if-let
Date: Thu, 29 Nov 2018 13:18:54 -0600

[Message part 1 (text/plain, inline)]

Hi -

I think this patch makes it much clearer that if-let functions like
let*, not let.

Thanks,
Alex

From 0504ba0c88bc63b527e54fc92e1923e60ff5759a Mon Sep 17 00:00:00 2001
From: Alex Branham <alex.branham <at> gmail.com>
Date: Thu, 29 Nov 2018 12:57:43 -0600
Subject: [PATCH] ; * lisp/emacs-lisp/subr-x.el (if-let): Improve docstring by
 mentioning let*

---
 lisp/emacs-lisp/subr-x.el | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/lisp/emacs-lisp/subr-x.el b/lisp/emacs-lisp/subr-x.el
index 7fab9083e8..8278f50d1d 100644
--- a/lisp/emacs-lisp/subr-x.el
+++ b/lisp/emacs-lisp/subr-x.el
@@ -158,9 +158,9 @@ are non-nil, then the result is non-nil."

 (defmacro if-let (spec then &rest else)
   "Bind variables according to SPEC and eval THEN or ELSE.
-Each binding is evaluated in turn, and evaluation stops if a
-binding value is nil.  If all are non-nil, the value of THEN is
-returned, or the last form in ELSE is returned.
+Each binding is evaluated in turn, as in `let*', and evaluation
+stops if a binding value is nil.  If all are non-nil, the value
+of THEN is returned, or the last form in ELSE is returned.

 Each element of SPEC is a list (SYMBOL VALUEFORM) which binds
 SYMBOL to the value of VALUEFORM.  An element can additionally be
--
2.19.1

[0001-lisp-emacs-lisp-subr-x.el-if-let-Improve-docstring-b.patch (text/x-patch, attachment)]

Message #8 received at 33550 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Alex Branham <alex.branham <at> gmail.com>
Cc: 33550 <at> debbugs.gnu.org
Subject: Re: bug#33550: [PATCH] mention let* in if-let
Date: Thu, 29 Nov 2018 21:43:19 +0200

> From: Alex Branham <alex.branham <at> gmail.com>
> Date: Thu, 29 Nov 2018 13:18:54 -0600
> 
> I think this patch makes it much clearer that if-let functions like
> let*, not let.

Doesn't "in turn" already say that?

Message #11 received at 33550 <at> debbugs.gnu.org (full text, mbox):

From: Alex Branham <alex.branham <at> gmail.com>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: 33550 <at> debbugs.gnu.org
Subject: Re: bug#33550: [PATCH] mention let* in if-let
Date: Thu, 29 Nov 2018 13:46:49 -0600

On Thu 29 Nov 2018 at 13:43, Eli Zaretskii <eliz <at> gnu.org> wrote:

>> I think this patch makes it much clearer that if-let functions like
>> let*, not let.
>
> Doesn't "in turn" already say that?

Yes, it does, you're completely right. This just emphasizes that if-let
acts like let* for those of us who perhaps skim documentation instead of
reading closely sometimes. I found it somewhat surprising that if-let
versus if-let* is not like let versus let*.

Alex

Message #14 received at 33550 <at> debbugs.gnu.org (full text, mbox):

From: Noam Postavsky <npostavs <at> gmail.com>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: Alex Branham <alex.branham <at> gmail.com>, 33550 <at> debbugs.gnu.org
Subject: Re: bug#33550: [PATCH] mention let* in if-let
Date: Wed, 17 Apr 2019 20:25:56 -0400

Eli Zaretskii <eliz <at> gnu.org> writes:

>> From: Alex Branham <alex.branham <at> gmail.com>
>> Date: Thu, 29 Nov 2018 13:18:54 -0600
>> 
>> I think this patch makes it much clearer that if-let functions like
>> let*, not let.
>
> Doesn't "in turn" already say that?

I think it's a bit ambiguous, it could refer to the fact that each
VALUEFORM is evaluted sequentially.  It's not entirely obvious that
previous SYMBOL bindings are available to follow VALUEFORMs, as in let*
rather than let (which would be the more obvious choice for if-let as
opposed to if-let*).

Message #17 received at 33550 <at> debbugs.gnu.org (full text, mbox):

From: Michael Heerdegen <michael_heerdegen <at> web.de>
To: Noam Postavsky <npostavs <at> gmail.com>
Cc: Eli Zaretskii <eliz <at> gnu.org>, 33550 <at> debbugs.gnu.org,
 Alex Branham <alex.branham <at> gmail.com>
Subject: Re: bug#33550: [PATCH] mention let* in if-let
Date: Thu, 18 Apr 2019 05:44:54 +0200

Noam Postavsky <npostavs <at> gmail.com> writes:

> I think it's a bit ambiguous, it could refer to the fact that each
> VALUEFORM is evaluted sequentially.  It's not entirely obvious that
> previous SYMBOL bindings are available to follow VALUEFORMs, as in let*
> rather than let

Yes, true.

> (which would be the more obvious choice for if-let as opposed to
> if-let*).

if-let mainly exists for backward compatibility (to support the "SPEC of
the form (SYMBOL SOMETHING)" case).  I don't recall why we didn't
obsolete it when we added if-let*, but AFAIR the special case had been
quite widely used.  Anyway, I think we should not change it.

Michael.

Message #20 received at 33550 <at> debbugs.gnu.org (full text, mbox):

From: Michael Heerdegen <michael_heerdegen <at> web.de>
To: Noam Postavsky <npostavs <at> gmail.com>
Cc: Eli Zaretskii <eliz <at> gnu.org>, 33550 <at> debbugs.gnu.org,
 Alex Branham <alex.branham <at> gmail.com>
Subject: Re: bug#33550: [PATCH] mention let* in if-let
Date: Thu, 18 Apr 2019 05:47:50 +0200

Michael Heerdegen <michael_heerdegen <at> web.de> writes:

> Anyway, I think we should not change it.

Sorry for having been unclear: I meant we shouldn't change the binding
behavior, I don't want to oppose clarifying the docstring.

Michael.

Message #23 received at 33550 <at> debbugs.gnu.org (full text, mbox):

From: Lars Ingebrigtsen <larsi <at> gnus.org>
To: Alex Branham <alex.branham <at> gmail.com>
Cc: 33550 <at> debbugs.gnu.org
Subject: Re: bug#33550: [PATCH] mention let* in if-let
Date: Sun, 23 Jun 2019 22:56:27 +0200

Alex Branham <alex.branham <at> gmail.com> writes:

>  (defmacro if-let (spec then &rest else)
>    "Bind variables according to SPEC and eval THEN or ELSE.
> -Each binding is evaluated in turn, and evaluation stops if a
> -binding value is nil.  If all are non-nil, the value of THEN is
> -returned, or the last form in ELSE is returned.
> +Each binding is evaluated in turn, as in `let*', and evaluation
> +stops if a binding value is nil.  If all are non-nil, the value
> +of THEN is returned, or the last form in ELSE is returned.

Yes, I think that's clearer, because it's a bit surprising that if-let
is more like let* than let.  I've now applied your change to the Emacs
trunk.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

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