From: "Pascal J. Bourguignon" <pjb@informatimago.com>
To: help-gnu-emacs@gnu.org
Subject: Re: no empty (zero) string predicate in Elisp
Date: Sun, 26 Apr 2015 06:06:48 +0200 [thread overview]
Message-ID: <87wq0zild3.fsf@kuiper.lan.informatimago.com> (raw)
In-Reply-To: mailman.1626.1430016741.904.help-gnu-emacs@gnu.org
Stefan Monnier <monnier@iro.umontreal.ca> writes:
>> Both for fundamental reasons, cardinals are built from a zero and a
>> successor relationship, therefore a predicate for zero is not stupid,
>> and a 1+ function neither;
>
> I know that you can model natural numbers from 0 and successor, but
> Elisp integers have very little to do with it and are not encoded in
> this way, and there isn't much code around that looks at them this way.
> So, as much as I like this way to look at the world, I don't find it
> helpful for Elisp.
This is exactly what I'm pointing to! If you want to consider how elisp
intgers are encoded on the native machine, then you definitely want a
zerop function, because there are BEQ and SEQ instructions.
>> and for optimization reasons on simplistic
>> compilers: the hardware usually HAS specific (and optimized)
>> instructions to test for zero and another to increment.
>
> C-h f zerop RET says:
>
> zerop is a compiled Lisp function in `subr.el'.
> [...]
> This function has a compiler macro `zerop--anon-cmacro'.
>
> and if you look at this mysterious zerop--anon-cmacro, you'll see that
> it optimizes `zerop' by rewriting it to (= 0 ...), which is implemented
> more efficiently.
Not in emacs-version "24.3.1" where I produced the disassembly
provided. But I'm happy to see it being optimized, this is one more
reason to keep it and use it.
--
__Pascal Bourguignon__ http://www.informatimago.com/
“The factory of the future will have only two employees, a man and a
dog. The man will be there to feed the dog. The dog will be there to
keep the man from touching the equipment.” -- Carl Bass CEO Autodesk
next prev parent reply other threads:[~2015-04-26 4:06 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-04-25 3:44 no empty (zero) string predicate in Elisp Emanuel Berg
2015-04-25 9:26 ` Nicolas Petton
2015-05-16 9:23 ` Nicolas Petton
2015-05-16 13:22 ` Bozhidar Batsov
2015-05-16 13:28 ` Bozhidar Batsov
2015-05-16 13:36 ` Bozhidar Batsov
2015-05-16 13:46 ` Eli Zaretskii
2015-05-16 16:17 ` Bozhidar Batsov
2015-05-16 13:43 ` Stefan Monnier
2015-05-16 15:27 ` Drew Adams
[not found] ` <mailman.1583.1429954907.904.help-gnu-emacs@gnu.org>
2015-04-25 11:22 ` Emanuel Berg
2015-04-25 13:30 ` Stefan Monnier
[not found] ` <mailman.1591.1429968677.904.help-gnu-emacs@gnu.org>
2015-04-25 14:48 ` Pascal J. Bourguignon
2015-04-26 2:52 ` Stefan Monnier
2015-04-27 10:28 ` zerop: compiler macro vs defsubst (was: no empty (zero) string predicate in Elisp) Nicolas Richard
2015-04-27 12:19 ` zerop: compiler macro vs defsubst Stefan Monnier
[not found] ` <mailman.1626.1430016741.904.help-gnu-emacs@gnu.org>
2015-04-26 4:06 ` Pascal J. Bourguignon [this message]
2015-04-26 21:25 ` no empty (zero) string predicate in Elisp Stefan Monnier
2015-04-26 4:26 ` Rusi
2015-04-26 12:36 ` Emanuel Berg
2015-04-26 15:03 ` Pascal J. Bourguignon
2015-04-26 18:34 ` Emanuel Berg
2015-04-26 18:59 ` Marcin Borkowski
[not found] ` <mailman.1658.1430074770.904.help-gnu-emacs@gnu.org>
2015-04-26 19:06 ` Emanuel Berg
2015-04-26 20:11 ` Marcin Borkowski
[not found] ` <mailman.1662.1430079142.904.help-gnu-emacs@gnu.org>
2015-04-27 1:00 ` Emanuel Berg
2015-04-26 17:28 ` Rusi
2015-04-26 18:39 ` Emanuel Berg
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