From: Barry Margolin <barmar@alum.mit.edu>
To: help-gnu-emacs@gnu.org
Subject: Re: Working with constansts
Date: Sun, 10 May 2009 14:59:56 -0400 [thread overview]
Message-ID: <barmar-9F5329.14595610052009@mara100-84.onlink.net> (raw)
In-Reply-To: mailman.6953.1241976532.31690.help-gnu-emacs@gnu.org
In article <mailman.6953.1241976532.31690.help-gnu-emacs@gnu.org>,
Richard Riley <rileyrgdev@googlemail.com> wrote:
> So really the question would be : why does Lisp not enforce constants
> being, err, constant?
Because this would incur overhead on every assignment, as it would have
to check whether the variable being assigned was declared as a constant.
Since this is so rarely the case, this overhead could be seen as mostly
wasted and unnecessary.
On the other hand, it would be nice if the byte compiler would warn
about this. Declaring a constant could put something in its property
list, and the compiler could then warn if it sees assignments to the
variable.
Some Common Lisp implementations get around the overhead problem by
putting constants in a page of VM marked read-only, so a hardware trap
is raised if an attempt is made to assign it.
--
Barry Margolin, barmar@alum.mit.edu
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***
*** PLEASE don't copy me on replies, I'll read them in the group ***
next prev parent reply other threads:[~2009-05-10 18:59 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-05-10 15:25 Working with constansts Decebal
2009-05-10 16:19 ` Pascal J. Bourguignon
2009-05-10 16:20 ` Richard Riley
2009-05-10 16:33 ` Pascal J. Bourguignon
2009-05-12 10:34 ` Nikolaj Schumacher
2009-05-10 17:02 ` Drew Adams
2009-05-10 17:28 ` Richard Riley
2009-05-11 7:39 ` Tassilo Horn
[not found] ` <mailman.6953.1241976532.31690.help-gnu-emacs@gnu.org>
2009-05-10 18:17 ` Pascal J. Bourguignon
2009-05-11 1:36 ` Richard Riley
2009-05-11 6:29 ` Pascal J. Bourguignon
2009-05-12 10:06 ` Nikolaj Schumacher
[not found] ` <mailman.7056.1242122790.31690.help-gnu-emacs@gnu.org>
2009-05-12 11:54 ` Pascal J. Bourguignon
2009-05-18 10:55 ` Nikolaj Schumacher
[not found] ` <7ceiuuczad.fsf@pbourguignon.informatimago.com>
[not found] ` <mailman.7379.1242644154.31690.help-gnu-emacs@gnu.org>
2009-05-18 12:20 ` Pascal J. Bourguignon
2009-05-18 19:19 ` Nikolaj Schumacher
2009-05-10 18:59 ` Barry Margolin [this message]
2009-05-11 1:38 ` Richard Riley
2009-05-12 9:44 ` Nikolaj Schumacher
[not found] ` <mailman.7052.1242121473.31690.help-gnu-emacs@gnu.org>
2009-05-12 11:43 ` Pascal J. Bourguignon
2009-05-13 4:59 ` Barry Margolin
2009-05-13 13:41 ` Ralf Wachinger
2009-05-13 21:23 ` Barry Margolin
2009-05-11 9:58 ` Thien-Thi Nguyen
[not found] ` <mailman.6988.1242036217.31690.help-gnu-emacs@gnu.org>
2009-05-12 1:31 ` Barry Margolin
2009-05-11 8:27 ` Decebal
2009-05-12 9:46 ` Nikolaj Schumacher
2009-05-10 16:31 ` Drew Adams
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