all messages for Emacs-related lists mirrored at yhetil.org
 help / color / mirror / code / Atom feed
From: Alan Mackenzie <acm@muc.de>
To: Eli Zaretskii <eliz@gnu.org>
Cc: 67116@debbugs.gnu.org, acm@muc.de,
	Stefan Monnier <monnier@iro.umontreal.ca>
Subject: bug#67116: byte-compile-let: reversing the order of evaluation of the clauses CAN make a difference.
Date: Sun, 12 Nov 2023 14:22:26 +0000	[thread overview]
Message-ID: <ZVDfoieRrbUtLZUV@ACM> (raw)
In-Reply-To: <83r0kvv6r0.fsf@gnu.org>

Hello, Eli.

On Sun, Nov 12, 2023 at 08:13:39 +0200, Eli Zaretskii wrote:
> > Cc: 67116@debbugs.gnu.org
> > Date: Sat, 11 Nov 2023 23:52:38 -0500
> > From:  Stefan Monnier via "Bug reports for GNU Emacs,
> >  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>

> > > In lisp/emacs-lisp/bytecomp.el (byte-compile-let), when the following
> > > form (from jit-lock--debug-fontify):

> > >                           (let
> > >                               ((beg pos)
> > >                                 (end (setq pos
> > >                                                (next-single-property-change
> > >                                                 pos 'fontified
> > >                                                 nil (point-max)))))
> > >                             (put-text-property beg end 'fontified nil)
> > >                             (jit-lock-fontify-now beg end))

> > > gets byte compiled, the order of evaluating BEG and END gets reversed so
> > > that END gets evaluated first.

> > Sounds like a bug.

> It does?  I always thought that the order of evaluation in a let form
> is unspecified, and in practice I had several bugs of exactly this
> nature, which I fixed by using let*, as expected.

No.  The order of _evaluation_ is specified as top to bottom.  The order
of _binding_ is unspecified.  Quoting from the elisp.info page "Local
Variables":

     All of the VALUE-FORMs in BINDINGS are evaluated in the order they
     appear and _before_ binding any of the symbols to them.

and a little later on the same page:

     On the other hand, the order of _bindings_ is unspecified:

> Why on Earth should we require any particular order of evaluation in a
> let form??

To make the value of a form unambiguous?  In any case, we do require a
particular order.

-- 
Alan Mackenzie (Nuremberg, Germany).





  reply	other threads:[~2023-11-12 14:22 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-11-11 22:48 bug#67116: byte-compile-let: reversing the order of evaluation of the clauses CAN make a difference Alan Mackenzie
2023-11-12  4:52 ` Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors
2023-11-12  6:13   ` Eli Zaretskii
2023-11-12 14:22     ` Alan Mackenzie [this message]
2023-11-12 19:32       ` Drew Adams
2023-11-14  2:56         ` Richard Stallman
2023-11-12 16:49     ` Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors
2023-11-12 14:54   ` Alan Mackenzie
2023-11-12 17:06     ` Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors
2023-11-12 14:21 ` Mattias Engdegård
2023-11-12 14:41   ` Mattias Engdegård
2023-11-13 11:19     ` Mattias Engdegård
2023-11-13 13:14       ` Alan Mackenzie

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=ZVDfoieRrbUtLZUV@ACM \
    --to=acm@muc.de \
    --cc=67116@debbugs.gnu.org \
    --cc=eliz@gnu.org \
    --cc=monnier@iro.umontreal.ca \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
Code repositories for project(s) associated with this external index

	https://git.savannah.gnu.org/cgit/emacs.git
	https://git.savannah.gnu.org/cgit/emacs/org-mode.git

This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.