Re: Guile's time execution issues

[Linus Björnstam]

Sorry, sent a premature reply. The problem is that some of those match blocks 
expand to using equal? which is a lot slower than using eqv? If we are doing it 
on every char in a 24mb file we are getting some serious constant factors. 

match is a syntax-rules macro, so distinguishing literals are not possible. 
Concerning "the macro writer's bill of rights" I could maybe think this it 
would be a rather nice thing to turn equal? to eqv? when one argument is a char 
literal :D

-- 
  Linus Björnstam

On Mon, 4 May 2020, at 11:36, Ludovic Courtès wrote:
> Hey!
> 
> Aleix Conchillo Flaqué <address@hidden> skribis:
> 
> > So weird I'm getting different numbers on 2.2.7. Not sure how I'm getting 
> > those initial ~20s and you are getting consistent ~ 45s. It
> > shouldn't have nothing to do with it, but could it be I'm running it on 
> > macOS?
> 
> Did you add this ‘->bool’ call to ensure the resulting alist is not kept
> in memory?
> 
> >  Now, it would be good to profile ‘json->scm’ to see if there’s anything
> >  that could be improved on the Guile side, or if it’s just a normal
> >  profile for GC-intensive code.
> >
> > Good news is that I have been working on performance improvements and 
> > json->scm is going down from my ~19 seconds to ~3
> > seconds on the same sample file. Linus Björnstam was the one to bring up 
> > performance issues so we've been back and forth trying to
> > make it fast.
> 
> Nice!
> 
> > 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…)
> 
> Thanks,
> Ludo’.
> 
>