Re: RE: Understanding the "let" construct and the setting of variables

[steve-humphreys@gmx.com]

> Sent: Thursday, December 17, 2020 at 5:55 PM
> From: "Drew Adams" <drew.adams@oracle.com>
> To: "Joost Kremers" <joostkremers@fastmail.fm>, steve-humphreys@gmx.com
> Cc: help-gnu-emacs@gnu.org
> Subject: RE: Understanding the "let" construct and the setting of variables
>
> > Yes, indeed. Variables bound with `let` or `let*` only exist inside the
> > `let`.
> > So as soon as you put the closing parenthesis matching the opening
> > parenthesis
> > directly before the `let`, the variables go out of scope and no longer exist.
> > (There are actually a couple of subtleties involved that make this statement
> > less than universally true, but those issues shouldn't concern a beginner.)
>
> This is not true of dynamically scoped, i.e. "special"
> vars.
>
> What is correct to say is that the let _binding_ of the
> variable no longer exists, not that the variable itself
> no longer exists.
>
> In the case of a dynamic variable, it continues to exist.
> And its binding from the let continues to exist as long
> as the code in the let body is executing.
>
> [Yes, some people will consider a let binding to create
> a _new_ variable.  In that sense you can say that that
> var ceases to exist.  But IMO that isn't as clear to
> users as it is to distinguish the binding from the var.
> And even if you use the words that way, you still need
> to point out that the var continues to exist as long as
> the code within the let body is executing (when the
> binding is for a dynamic var).]

I would thing the variable has to be made somewhere.
In fact people talk about "unboundp".

> The best explanation of let binding in Elisp is in the
> Common Lisp doc, IMO.  In particular, CLTL2's explanation
> of dynamic and lexical binding is quite clear.  It applies
> equally to Elisp.
>
> https://www.cs.cmu.edu/Groups/AI/html/cltl/clm/node43.html
>
>