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Re: Working with constansts
From: |
Barry Margolin |
Subject: |
Re: Working with constansts |
Date: |
Sun, 10 May 2009 14:59:56 -0400 |
User-agent: |
MT-NewsWatcher/3.5.3b3 (Intel Mac OS X) |
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 ***
- Re: Working with constansts, (continued)
- Message not available
- Re: Working with constansts, Pascal J. Bourguignon, 2009/05/10
- Re: Working with constansts, Richard Riley, 2009/05/10
- Re: Working with constansts, Pascal J. Bourguignon, 2009/05/11
- Re: Working with constansts, Nikolaj Schumacher, 2009/05/12
- Message not available
- Re: Working with constansts, Pascal J. Bourguignon, 2009/05/12
- Re: Working with constansts, Nikolaj Schumacher, 2009/05/18
- Message not available
- Message not available
- Message not available
- Re: Working with constansts, Pascal J. Bourguignon, 2009/05/18
- Re: Working with constansts, Nikolaj Schumacher, 2009/05/18
- Message not available
- Re: Working with constansts,
Barry Margolin <=
- Re: Working with constansts, Richard Riley, 2009/05/10
- Re: Working with constansts, Nikolaj Schumacher, 2009/05/12
- Message not available
- Re: Working with constansts, Pascal J. Bourguignon, 2009/05/12
- Message not available
- Re: Working with constansts, Barry Margolin, 2009/05/13
- Re: Working with constansts, Ralf Wachinger, 2009/05/13
- Re: Working with constansts, Barry Margolin, 2009/05/13
- Re: Working with constansts, Thien-Thi Nguyen, 2009/05/11
- Message not available
- Re: Working with constansts, Barry Margolin, 2009/05/11
Re: Working with constansts, Decebal, 2009/05/11