From: <tomas@tuxteam.de>
To: emacs-devel@gnu.org
Subject: Re: PATCH: Explicitly show how let works on global-variables
Date: Tue, 4 Oct 2022 09:59:17 +0200 [thread overview]
Message-ID: <Yzvn1XDBOBVYP1J/@tuxteam.de> (raw)
In-Reply-To: <CAO48Bk_9Wksepn2PQV-DPxGYAi4KXN6gfUQkZaFp1DV6HQrNAg@mail.gmail.com>
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On Tue, Oct 04, 2022 at 08:46:02AM +0200, Pedro Andres Aranda Gutierrez wrote:
> Hi
>
> this is a small patch for the 'Introduction to Emacs LISP programming'
> guide to show how let works on system-wide variables.
> Understanding this would have made my life easier the past +20 years ;-)
> and an example is sometimes worth 100 lines of explanation (more so if you
> are in a hurry and you do diagonal reading)
>
> Best, /PA
[...]
> +@need 1500
> +When you use a system-wide variable in @code{let}, its value is modified in its
> +scope and then restored. As an example, the following snippet manipulates
> +@code{system-time-locale} in the scope of the @code{let} only:
> +
I think this is technically wrong and potentially confusing.
I'd tend to say that a new binding is created which shadows the
global binding. The `system-time-locale' in your let-bound scope
is a different variable from the global one, although it has the
same name.
More importantly, nothing gets "restored": it's just the compiler
which sees a different variable depending on scope. This is even
"more true" (I know, I know) with lexical variables.
The example itself seems to me a good idea. Just the mental model
needs fixing :)
Cheers
--
t
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next prev parent reply other threads:[~2022-10-04 7:59 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-04 6:46 PATCH: Explicitly show how let works on global-variables Pedro Andres Aranda Gutierrez
2022-10-04 7:52 ` Eli Zaretskii
2022-10-04 8:09 ` Pedro Andres Aranda Gutierrez
2022-10-04 11:36 ` Phil Sainty
2022-10-04 13:43 ` Stefan Monnier
2022-10-04 22:22 ` Tim Cross
2022-10-05 5:28 ` Pedro Andres Aranda Gutierrez
2022-10-06 9:00 ` Pedro Andres Aranda Gutierrez
2022-10-06 19:34 ` Emanuel Berg
2022-10-04 17:39 ` Richard Stallman
2022-10-04 7:59 ` tomas [this message]
2022-10-04 11:56 ` Phil Sainty
2022-10-04 13:48 ` Stefan Monnier
2022-10-05 21:31 ` Richard Stallman
2022-10-04 15:00 ` [External] : " Drew Adams
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