unofficial mirror of guile-devel@gnu.org 
 help / color / mirror / Atom feed
From: "Linus Björnstam" <linus.bjornstam@veryfast.biz>
To: "Ludovic Courtès" <ludo@gnu.org>
Cc: "Aleix Conchillo Flaqué" <aconchillo@gmail.com>,
	guile-user <guile-user@gnu.org>,
	guile-devel <guile-devel@gnu.org>
Subject: Re: Guile's time execution issues
Date: Mon, 04 May 2020 22:50:25 +0200	[thread overview]
Message-ID: <d7951a62-a1df-44e2-bbc0-2fb9e0bc4079@www.fastmail.com> (raw)
In-Reply-To: <874ksvqx7k.fsf@gnu.org>

You didn't see my other reply. The matching code isn't suboptimal. The equality predicate is  The problem is that match compares using equal? even for literal chars (where eqv? is a lot faster). It would be a rather trivial optimization to do, either to match.scm (meaning: breaking with upstream and use syntax-case) or to the guile compiler in general (changing equal? to eqv, when there are character literals), which seems ok-ish for this use-case but at very little benefit in general.

A long-term goal of mine is to write a pattern matcher with the optimisations that the racket matcher does (among other things: some serious list matching reordering!). That is a daunting task though.

-- 
  Linus Björnstam

On Mon, 4 May 2020, at 22:09, Ludovic Courtès wrote:
> Hi,
> 
> Linus Björnstam <linus.bjornstam@veryfast.biz> skribis:
> 
> > On Mon, 4 May 2020, at 11:36, Ludovic Courtès wrote:
> >  
> >> > One thing I found is that `match` is slow. The code looked nicer but had to change it back to lets and conds as the performance
> >> > increase was ~2 seconds.
> >> 
> >> Oh, in which case exactly?  And are you sure your hand-written code is
> >> equivalent to the ‘match’ code (it’s common for hand-written code to be
> >> more lax than ‘match’)?
> >> 
> >> One thing to pay attention to is the use of ‘list?’, which is O(N), and
> >> is implied by ellipses in ‘match’.  If you want to use ‘match’ in a way
> >> that avoids ‘list?’, write patterns such as (a . b) instead of (a b ...).
> >> It doesn’t have the same meaning, but often the end result is the same,
> >> for instance because you’ll later match on ‘b’ anyway.
> >> 
> >> (I wish we can one day have a proper list type disjoint from pairs…)
> >
> > The change is here: he is only matching against chars and predicates: https://github.com/aconchillo/guile-json/commit/ad4b06d86e4822466983d00f55474c8f664b538d
> 
> It would be nice if you could pinpoint which one of these changes causes
> a difference, because:
> 
> --8<---------------cut here---------------start------------->8---
> scheme@(guile-user)> ,optimize (match (peek-char port) ((? eof-object?) 
> x) ((? whitespace?) w) (_ e))
> $84 = (let ((v (peek-char port)))
>   (cond ((eof-object? v) x)
>         ((whitespace? v) w)
>         (else e)))
> --8<---------------cut here---------------end--------------->8---
> 
> What might make a difference is the code bloat when using ‘or’:
> 
> --8<---------------cut here---------------start------------->8---
> scheme@(guile-user)> ,optimize (match (peek-char port) ((or #\a #\b #\c #\d) x))
> $86 = (let ((v (peek-char port)))
>   (cond ((equal? v #\a) x)
>         ((equal? v #\b) x)
>         ((equal? v #\c) x)
>         ((equal? v #\d) x)
>         (else
>          ((@@ (ice-9 match) error)
>           'match
>           "no matching pattern"
>           v)
>          #f)))
> --8<---------------cut here---------------end--------------->8---
> 
> but even that sounds unlikely.
> 
> You’re compiling with -O2, right?
> 
> Thanks,
> Ludo’.
>



  reply	other threads:[~2020-05-04 20:50 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-21 22:03 Guile's time execution issues Aleix Conchillo Flaqué
2020-04-22 13:47 ` Linus Björnstam
2020-04-26 17:16 ` Ludovic Courtès
2020-04-26 23:14   ` Aleix Conchillo Flaqué
2020-05-02 14:11     ` Ludovic Courtès
2020-05-04  0:32       ` Aleix Conchillo Flaqué
2020-05-04  9:36         ` Ludovic Courtès
2020-05-04 11:19           ` Linus Björnstam
2020-05-04 20:09             ` Ludovic Courtès
2020-05-04 20:50               ` Linus Björnstam [this message]
2020-05-08 11:31                 ` Linus Björnstam
2020-05-04 18:47           ` Linus Björnstam

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

  List information: https://www.gnu.org/software/guile/

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=d7951a62-a1df-44e2-bbc0-2fb9e0bc4079@www.fastmail.com \
    --to=linus.bjornstam@veryfast.biz \
    --cc=aconchillo@gmail.com \
    --cc=guile-devel@gnu.org \
    --cc=guile-user@gnu.org \
    --cc=ludo@gnu.org \
    /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.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).