bug#33550: [PATCH] mention let* in if-let

bug#33550: [PATCH] mention let* in if-let

[Alex Branham]

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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@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



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From 0504ba0c88bc63b527e54fc92e1923e60ff5759a Mon Sep 17 00:00:00 2001
From: Alex Branham <alex.branham@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

bug#33550: [PATCH] mention let* in if-let

[Eli Zaretskii]

> From: Alex Branham <alex.branham@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?

bug#33550: [PATCH] mention let* in if-let

[Alex Branham]

On Thu 29 Nov 2018 at 13:43, Eli Zaretskii <eliz@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

bug#33550: [PATCH] mention let* in if-let

[Noam Postavsky]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Alex Branham <alex.branham@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*).

bug#33550: [PATCH] mention let* in if-let

[Michael Heerdegen]

Noam Postavsky <npostavs@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.

bug#33550: [PATCH] mention let* in if-let

[Michael Heerdegen]

Michael Heerdegen <michael_heerdegen@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.

bug#33550: [PATCH] mention let* in if-let

[Lars Ingebrigtsen]

Alex Branham <alex.branham@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