From: Philipp Stephani <p.stephani2@gmail.com>
To: Eli Zaretskii <eliz@gnu.org>
Cc: 25154@debbugs.gnu.org, agrambot@gmail.com, tino.calancha@gmail.com
Subject: bug#25154: 25.1; Bindings in cl-letf are in reverse order
Date: Fri, 23 Dec 2016 12:17:54 +0000 [thread overview]
Message-ID: <CAArVCkS=F6ZGwSBgum-ST31t_0+nY9oRAkqFofSb4FHFXYdCZA@mail.gmail.com> (raw)
In-Reply-To: <83r35fg9jq.fsf@gnu.org>
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Eli Zaretskii <eliz@gnu.org> schrieb am Sa., 10. Dez. 2016 um 15:09 Uhr:
> > From: Philipp Stephani <p.stephani2@gmail.com>
> > Date: Sat, 10 Dec 2016 13:41:16 +0000
> > Cc: 25154@debbugs.gnu.org, Alex <agrambot@gmail.com>
> >
> > > Isn't it true that the order of evaluation in a 'let' is unspecified?
> > > If you want a particular order, use 'let*'.
> > Right, the order of evaluation in a let is up to the implementation. A
> program
> > should not rely on such details.
> > The same statement should apply to cl-letf.
> >
> > I think that should be mentioned explicitly in the manuals: given that
> the order of value evaluations is specified,
> > people might expect the same for the bindings themselves.
>
> I agree, patches to that effect are welcome. (AFAICT, the manual
> tries to say that already, but the wording could be more explicit.)
>
OK, I've attached a patch that hopefully clarifies this a bit.
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From 42d7450c41d69a713eb8f9492cc169e8c2bc15ca Mon Sep 17 00:00:00 2001
From: Philipp Stephani <phst@google.com>
Date: Fri, 23 Dec 2016 13:14:55 +0100
Subject: [PATCH] Document that variable binding order is unspecified
* doc/lispref/variables.texi (Local Variables):
* cl.texi (Modify Macros): Document that assignment order in 'let' and
'cl-letf' is unspecified.
---
doc/lispref/variables.texi | 12 ++++++++++++
doc/misc/cl.texi | 5 +++++
2 files changed, 17 insertions(+)
diff --git a/doc/lispref/variables.texi b/doc/lispref/variables.texi
index a2d64815d9..e2c8c542ab 100644
--- a/doc/lispref/variables.texi
+++ b/doc/lispref/variables.texi
@@ -221,6 +221,18 @@ Local Variables
@result{} (1 2)
@end group
@end example
+
+On the other hand, the order of @emph{assignments} is unspecified: in
+the following example, either 1 or 2 might be printed.
+
+@example
+(let ((x 1)
+ (x 2))
+ (print x))
+@end example
+
+Therefore, avoid binding a variable more than once in a single
+@code{let} form.
@end defspec
@defspec let* (bindings@dots{}) forms@dots{}
diff --git a/doc/misc/cl.texi b/doc/misc/cl.texi
index c62fa727c1..aa047e2122 100644
--- a/doc/misc/cl.texi
+++ b/doc/misc/cl.texi
@@ -1179,6 +1179,11 @@ Modify Macros
as @code{setf} places; each will accept either an integer or a
marker as the stored value.)
+Like in the case of @code{let}, the @var{value} forms are evaluated in
+the order they appear, but the order of assignments is unspecified.
+Therefore, avoid assigning to the same @var{place} more than once in a
+single @code{cl-letf} form.
+
Since generalized variables look like lists, @code{let}'s shorthand
of using @samp{foo} for @samp{(foo nil)} as a @var{binding} would
be ambiguous in @code{cl-letf} and is not allowed.
--
2.11.0
next prev parent reply other threads:[~2016-12-23 12:17 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-12-09 23:36 bug#25154: 25.1; Bindings in cl-letf are in reverse order Alex
2016-12-10 4:29 ` Alex
2016-12-10 7:22 ` Eli Zaretskii
2016-12-10 7:43 ` Tino Calancha
2016-12-10 13:41 ` Philipp Stephani
2016-12-10 14:01 ` Tino Calancha
2016-12-10 14:09 ` Eli Zaretskii
2016-12-23 12:17 ` Philipp Stephani [this message]
2016-12-23 12:46 ` Tino Calancha
2016-12-23 13:53 ` Eli Zaretskii
2016-12-23 16:30 ` Philipp Stephani
2016-12-10 18:05 ` Alex
2016-12-10 18:14 ` npostavs
2016-12-10 19:41 ` Alex
2016-12-10 18:27 ` Eli Zaretskii
2016-12-10 19:52 ` Alex
2016-12-11 3:11 ` Tino Calancha
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