From: Philipp Stephani <p.stephani2@gmail.com>
To: Stefan Monnier <monnier@iro.umontreal.ca>
Cc: emacs-devel@gnu.org
Subject: Re: pure-fns in byte-opt.el
Date: Fri, 28 Jul 2017 17:45:48 +0000 [thread overview]
Message-ID: <CAArVCkTOX5BSzxQR4XqPvnXCNPohAQAeKEzbFLO6+DjZMuzKrA@mail.gmail.com> (raw)
In-Reply-To: <jwvpocomcol.fsf-monnier+Inbox@gnu.org>
[-- Attachment #1: Type: text/plain, Size: 1266 bytes --]
Stefan Monnier <monnier@iro.umontreal.ca> schrieb am Di., 25. Juli 2017 um
23:27 Uhr:
> > Why? Its return value clearly only depends on its argument, and it
> doesn't
> > change any global state. It's the poster child of a pure function!
>
> (let ((s (make-string 5 ?a)))
> (list (string-to-char s)
> (progn
> (aset s 0 ?b)
> (string-to-char s))))
>
> If string-to-char were a pure function, it would return the same value
> in both calls (since the arguments are `eq').
>
>
Hmm. I get the argument, but wouldn't that mean that only a tiny set of
builtins were pure? If the definition is "A function is pure if applying it
to the same objects (in the sense of `eq') always gives the same result",
then I think only eq, eql, null, and the type predicates (integerp etc.)
are pure. Even the arithmetic functions aren't pure because they can act on
(mutable) markers. The list in byte-opt, however, is noticeably different,
and none of the functions marked pure there are actually pure. The same
applies to third-party libraries such as dash.el.
In any case, the precise definition of "pure" and "side effect free" needs
to be in the manual, and functions that are wrongly declared as pure or
side effect free need to be fixed.
[-- Attachment #2: Type: text/html, Size: 1669 bytes --]
next prev parent reply other threads:[~2017-07-28 17:45 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-07-25 2:06 pure-fns in byte-opt.el Mark Oteiza
2017-07-25 8:14 ` Andreas Schwab
2017-07-25 14:16 ` Stefan Monnier
2017-07-25 20:57 ` Philipp Stephani
2017-07-25 21:27 ` Stefan Monnier
2017-07-25 22:28 ` Clément Pit-Claudel
2017-07-26 0:08 ` Stefan Monnier
2017-07-26 7:39 ` Clément Pit-Claudel
2017-07-26 12:58 ` Stefan Monnier
2017-07-28 17:45 ` Philipp Stephani [this message]
2017-07-28 17:49 ` Stefan Monnier
2017-07-28 17:52 ` Philipp Stephani
2017-07-28 22:20 ` Stefan Monnier
2017-09-24 7:31 ` Philipp Stephani
2017-09-24 16:23 ` Stefan Monnier
2017-09-25 22:06 ` Richard Stallman
2017-09-26 0:25 ` Stefan Monnier
2020-07-25 19:53 ` Philipp Stephani
2020-07-25 19:58 ` Stefan Monnier
2020-07-25 20:08 ` Philipp Stephani
2020-07-25 20:59 ` Stefan Monnier
2020-07-29 14:21 ` Philipp Stephani
2020-07-29 14:25 ` Stefan Monnier
2017-09-24 16:26 ` Drew Adams
2017-07-26 1:00 ` Mark Oteiza
2017-07-26 14:33 ` Eli Zaretskii
2017-07-27 2:36 ` Mark Oteiza
2017-07-27 2:46 ` Stefan Monnier
2017-07-29 16:43 ` Mark Oteiza
2017-07-29 17:22 ` Eli Zaretskii
2017-07-29 19:48 ` Mark Oteiza
2017-07-29 20:03 ` Andreas Schwab
2017-07-29 20:14 ` Mark Oteiza
2017-07-27 17:06 ` Eli Zaretskii
2017-07-28 0:24 ` Mark Oteiza
2017-07-28 7:02 ` Eli Zaretskii
2017-07-29 1:24 ` Mark Oteiza
2017-07-29 7:24 ` Eli Zaretskii
2017-07-29 16:34 ` Mark Oteiza
2017-07-29 17:21 ` Eli Zaretskii
2017-09-24 7:34 ` Philipp Stephani
2017-09-24 16:24 ` Stefan Monnier
2017-09-24 23:22 ` John Wiegley
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CAArVCkTOX5BSzxQR4XqPvnXCNPohAQAeKEzbFLO6+DjZMuzKrA@mail.gmail.com \
--to=p.stephani2@gmail.com \
--cc=emacs-devel@gnu.org \
--cc=monnier@iro.umontreal.ca \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
Code repositories for project(s) associated with this external index
https://git.savannah.gnu.org/cgit/emacs.git
https://git.savannah.gnu.org/cgit/emacs/org-mode.git
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.