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Re: Possible defvar bug
From: |
Thierry Volpiatto |
Subject: |
Re: Possible defvar bug |
Date: |
Mon, 18 Feb 2013 16:41:12 +0100 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/24.2.93 (gnu/linux) |
Alan Mackenzie <address@hidden> writes:
> On Mon, Feb 18, 2013 at 04:00:28PM +0100, Didier Verna wrote:
>> Jambunathan K <address@hidden> wrote:
>
>> > I am certain I don't understand what these paragraphs mean,
>> > particularly the second one.
>> > lands.
>
>> > ,---- C-h f
>> > | If SYMBOL has a local binding, then this form affects the local
>> > | binding. This is usually not what you want. Thus, if you need to
>> > | load a file defining variables, with this form or with `defconst' or
>> > | `defcustom', you should always load that file _outside_ any bindings
>> > | for these variables. (`defconst' and `defcustom' behave similarly in
>> > | this respect.)
>> > `----
>
>> This means that:
>
>> ELISP> (let ((foo 3))
>> (defvar foo 1)
>> (print foo))
>> 3
>> ELISP> foo
>> *** Eval error *** Symbol's value as variable is void: foo
>> ELISP>
>
>
>> And, no, this is almost never what you want :-) Just like Tassilo
>> noticed by accident.
>
> Why would anybody want to defvar a variable inside a let binding which
> also defines it, anyway? It may not be totally invalid, but it's
> certainly in breach of good taste. I would argue that the current
> behaviour _is_ what is wanted, since it alerts one to a probable error.
See also documentation of `require' which should not be used inside
`let' bindings for same reasons.
--
Thierry
Get my Gnupg key:
gpg --keyserver pgp.mit.edu --recv-keys 59F29997
Re: Possible defvar bug, Glenn Morris, 2013/02/18