GNU bug report logs - #8711
24.0.50; binding _ to unused values with lexical-binding

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Message #44 received at 8711 <at> debbugs.gnu.org (full text, mbox):

From: Juanma Barranquero <lekktu <at> gmail.com>
To: Stefan Monnier <monnier <at> iro.umontreal.ca>
Cc: 8711 <at> debbugs.gnu.org, Helmut Eller <eller.helmut <at> gmail.com>
Subject: Re: bug#8711: 24.0.50; binding _ to unused values with lexical-binding
Date: Thu, 2 Jun 2011 15:41:32 +0200

On Thu, Jun 2, 2011 at 14:45, Stefan Monnier <monnier <at> iro.umontreal.ca> wrote:

> That's how dolist/dotimes are defined in Common-Lisp, hence that's
> how it works in cl-macs.  The subr versions also do it because when we
> introduced them, some people brought up the issue and it seemed there
> was no point in being incompatible.

I wonder what kind of code (other than a specific test) makes this
incompatibility noticeable in the first place... but I digress ;-)

> Yes, I do find it very odd as well, but CLHS says clearly "At the time
> result-form is processed, var is bound to nil".

Silly me, I should've checked the CLHS. I would still be puzzled, but
at least not by Emacs.

> Or she can just use different names rather than reusing the same
> variable name.

Yeah, that too.

>> so setting it to nil in the (dolist (VAR LIST RESULT) ...) case does
>> not bring any clear benefit, even in the non-lexical case.
>
> Agreed.

Well, at the very least that's something that could/should be
optimized away (at some point in the future, I mean) in the
lexical-binding case (I think we already have some macros that expand
to different code for lexical and non-lexical compilations?).

Meanwhile, will you complain if I change that particular case (in
doc-view.el) to be like

(let (...)
  (dolist (var list)
    ...)
  result)

to avoid the warning?

    Juanma

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