From: Stefan Monnier <monnier@iro.umontreal.ca>
To: help-gnu-emacs@gnu.org
Subject: Re: no empty (zero) string predicate in Elisp
Date: Sat, 25 Apr 2015 22:52:00 -0400 [thread overview]
Message-ID: <jwv8udfd2ry.fsf-monnier+gmane.emacs.help@gnu.org> (raw)
In-Reply-To: 874mo4jmb7.fsf@kuiper.lan.informatimago.com
> 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.
> 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.
Stefan
next prev parent reply other threads:[~2015-04-26 2:52 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 [this message]
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 ` no empty (zero) string predicate in Elisp Pascal J. Bourguignon
2015-04-26 21:25 ` 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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