From: Stefan Monnier <monnier@iro.umontreal.ca>
To: emacs-devel@gnu.org
Subject: Re: pure-fns in byte-opt.el
Date: Sun, 24 Sep 2017 12:23:29 -0400 [thread overview]
Message-ID: <jwv1smwrsdb.fsf-monnier+gmane.emacs.devel@gnu.org> (raw)
In-Reply-To: CAArVCkQ02yOBuuB=ceDD8WV--XbttqzLXP2stv2ic61v+PuKSg@mail.gmail.com
> A side-effect-free function is one where all of the following is true:
> - After exiting the function (whether normally or nonlocally), the
> `match-data' are `equal' to the `match-data' before entering the function.
> - After exiting the function, all dynamic variables, their default values,
> their symbol cells, etc., are `eq' to the respective values before entering
> the function. Exceptions are variables only used for debugging/tracing,
> such as `cons-cells-consed'.
> - All buffer contents, markers, point values etc. are
> `equal-including-properties' to their previous values.
> - The same buffers and threads still exist.
I don't think we want to enumerate all the manners that side-effects can
occur, since we will inevitably forget some (and the list will get out
of date).
I think we should define it more as something like:
side-effect-free means: if the result of the function is not used,
calling the function or not does not affect the behavior of the program,
except that the function may signal an error.
side-effect-and-error-free means: like side-effect-free but cannot
signal an error. This means that the optimizer can eliminate calls
to those functions if the result is not used.
pure: like side-effect-free but additionally, the function always
returns the same value when called with the same arguments, so the
compiler can precompute the call if it knows the arguments.
-- Stefan
next prev parent reply other threads:[~2017-09-24 16:23 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
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 [this message]
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
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