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Re: The purpose of makunbound
From: |
Stephen J. Turnbull |
Subject: |
Re: The purpose of makunbound |
Date: |
Fri, 20 Feb 2015 11:58:14 +0900 |
Kelly Dean writes:
> The implementation does see [the two forms of unbinding] as
> different,
I don't understand what you mean. The unbinding is the same, and has
the conventional semantics: this value can no longer be accessed by
that name (== symbol). Exit from let has *additional semantics* of
restoring the previous binding.
The void or unbound pseudo-value is an implementation detail, useful
in so-called shallow-binding implementations. You can't observe that
symbol from Lisp without making an end-run around the Lisp engine (eg,
via an FFI). It's uninterned so it's not possible to find it and then
store it somewhere, and all slot-accessing internal functions check
for it and error if it's found.
> In contrast, if makunbound didn't work for let-bound or
> buffer-local variables,
If there's a reason for makunbound in the top-level environment, the
same reason will apply to let-bound environments. I can't support
your proposal to error on makunbound of let-bound variables.
- Re: The purpose of makunbound, (continued)
- Re: The purpose of makunbound, Kelly Dean, 2015/02/21
- Re: The purpose of makunbound, Kelly Dean, 2015/02/19
- Re: The purpose of makunbound, Stefan Monnier, 2015/02/19
- Re: The purpose of makunbound, Kelly Dean, 2015/02/19
- Re: The purpose of makunbound, Stefan Monnier, 2015/02/19
- Re: The purpose of makunbound, Kelly Dean, 2015/02/20
- Re: The purpose of makunbound, Stefan Monnier, 2015/02/20
- Re: The purpose of makunbound,
Stephen J. Turnbull <=
- Re: The purpose of makunbound, Richard Stallman, 2015/02/19
- Re: The purpose of makunbound, Kelly Dean, 2015/02/20
- Re: The purpose of makunbound, Richard Stallman, 2015/02/20
- Re: The purpose of makunbound, Stephen J. Turnbull, 2015/02/21
- Re: The purpose of makunbound, Kelly Dean, 2015/02/21
- Re: The purpose of makunbound, Andreas Schwab, 2015/02/22
- Re: [PATCH] (Updated) Run hook when variable is set, Kelly Dean, 2015/02/18
- Re: [PATCH] (Updated) Run hook when variable is set, Stefan Monnier, 2015/02/18
- Re: [PATCH] (Updated) Run hook when variable is set, Stefan Monnier, 2015/02/18
- Re: [PATCH] (Updated) Run hook when variable is set, Kelly Dean, 2015/02/19