From: Emanuel Berg <embe8573@student.uu.se>
To: help-gnu-emacs@gnu.org
Subject: Re: obarray
Date: Tue, 17 Dec 2013 03:11:45 +0100 [thread overview]
Message-ID: <87r49cp6o5.fsf@nl106-137-194.student.uu.se> (raw)
In-Reply-To: mailman.9442.1387244871.10748.help-gnu-emacs@gnu.org
Michael Heerdegen <michael_heerdegen@web.de> writes:
>> Is there a way to confirm this? How can I access a
>> symbol's value, if the symbol isn't in the obarray?
>> If it isn't in the obarray, where is it? Is there a
>> buffer and/or "scope" (i.e. form or process)
>> local/temporary object array or anything of the
>> like?
>
> No. They are just existing in memory, and will not be
> garage collected, as long as they can be referenced
> from Lisp. There is also no array of all existing
> strings, of all window configurations, etc. So you
> can't tell Lisp to give you a complete list of all
> currently existing strings, window configurations, or
> (uninterned) symbols. There is just no need to
> organize those objects in a user visible structure.
OK.
> OTOH, an uninterned symbol can be used like any other
> symbol: it can be set, used to hold a function, etc.
>
>> You can access it the same way you can access the
>> contents of arrays and lists -- by getting to it from
>> some other variable (or cons cell or array element)
>> that references it. That's what the variable
>> uninterned-symbol is for. (symbol-value
>> uninterned-symbol) => bar
>
> Of course, this is not very useful, it was just a
> demonstration, not a realistic use case.
Yes :)
> When using uninterned symbols in macros, you can
> "paste" these symbols in the expansion code which
> will be evaluated at run-time. So, programs _can_
> contain uninterned symbols; you can really _use_
> uninterned symbols in code. Not in code read from a
> file or buffer, but in code generated by macros.
> This way, you avoid that you accidentally use a
> symbol that is already "in use" (e.g. in the code the
> macro transforms).
Yes, this much I understood, only it was hard to
visualize in practice. So: the macro accept code *as
arguments* (code that isn't evaluated) and transforms
that code? Then I get it. I thought the macro just
produced new code, in what case I can't see how it
could be useful because either no one knows about the
macro so no one will use any symbols it may setup, *or*
the macro knows about itself so any references to what
is setup locally will be correct.
--
Emanuel Berg, programmer-for-rent. CV, projects, etc at uXu
underground experts united: http://user.it.uu.se/~embe8573
next prev parent reply other threads:[~2013-12-17 2:11 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-12-15 0:54 obarray Emanuel Berg
2013-12-15 1:14 ` obarray Juanma Barranquero
[not found] ` <mailman.9268.1387070101.10748.help-gnu-emacs@gnu.org>
2013-12-15 1:37 ` obarray Emanuel Berg
2013-12-15 1:56 ` obarray Michael Heerdegen
2013-12-15 1:59 ` obarray Juanma Barranquero
[not found] ` <mailman.9271.1387072648.10748.help-gnu-emacs@gnu.org>
2013-12-15 4:17 ` obarray Emanuel Berg
2013-12-15 4:17 ` obarray Barry Margolin
2013-12-15 4:47 ` obarray Michael Heerdegen
2013-12-15 4:55 ` obarray Emanuel Berg
2013-12-15 6:04 ` obarray Barry Margolin
2013-12-15 17:43 ` obarray Emanuel Berg
2013-12-16 17:44 ` obarray Barry Margolin
2013-12-17 1:47 ` obarray Michael Heerdegen
[not found] ` <mailman.9442.1387244871.10748.help-gnu-emacs@gnu.org>
2013-12-17 2:11 ` Emanuel Berg [this message]
2013-12-17 2:55 ` obarray Michael Heerdegen
[not found] ` <mailman.9452.1387248989.10748.help-gnu-emacs@gnu.org>
2013-12-17 3:01 ` obarray Emanuel Berg
2013-12-17 17:32 ` obarray Barry Margolin
2013-12-17 17:42 ` obarray Emanuel Berg
[not found] ` <mailman.9279.1387082898.10748.help-gnu-emacs@gnu.org>
2013-12-15 5:11 ` obarray Emanuel Berg
2013-12-15 5:36 ` obarray Emanuel Berg
2013-12-15 6:17 ` obarray Michael Heerdegen
[not found] ` <mailman.9283.1387088419.10748.help-gnu-emacs@gnu.org>
2013-12-15 17:51 ` obarray Emanuel Berg
2013-12-15 6:15 ` obarray Michael Heerdegen
[not found] ` <mailman.9282.1387088166.10748.help-gnu-emacs@gnu.org>
2013-12-15 17:47 ` obarray Emanuel Berg
2013-12-15 5:58 ` obarray Barry Margolin
2013-12-15 17:28 ` obarray Emanuel Berg
2013-12-17 14:38 ` obarray jack-mac
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