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Re: PATCH: Explicitly show how let works on global-variables

From: tomas
Subject: Re: PATCH: Explicitly show how let works on global-variables
Date: Tue, 4 Oct 2022 09:59:17 +0200

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 :)


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