From: ludo@gnu.org (Ludovic Courtès)
To: Andy Wingo <wingo@pobox.com>
Cc: guile-devel@gnu.org
Subject: Re: early termination for `map'
Date: Thu, 05 May 2011 22:21:27 +0200 [thread overview]
Message-ID: <87r58clwzc.fsf@gnu.org> (raw)
In-Reply-To: <m3iptpvvmf.fsf@unquote.localdomain> (Andy Wingo's message of "Thu, 05 May 2011 20:40:40 +0200")
Andy Wingo <wingo@pobox.com> writes:
> On Thu 05 May 2011 18:26, ludo@gnu.org (Ludovic Courtès) writes:
>
>> Andy Wingo <wingo@pobox.com> writes:
>>
>>> If you call `map' or `for-each' with more than one list, our versions of
>>> these operators will detect if the lists are of unequal length, and
>>> throw an error in that case.
>>>
>>> However, SRFI-1 has long provided an extension to this, to allow for
>>> early termination when any of the lists runs out. R6RS adopted this,
>>> and it looks like R7RS will ratify that.
>>>
>>> So perhaps it's time for us to change as well.
>>
>> To change the default ‘map’ & ‘for-each’ to do like SRFI-1’s, right?
>
> Yeah, that was the proposal; but the argument is a bit weaker, now that
> I found that the R6RS did not go with this change. So I don't really
> know.
Oh, OK.
> The reason I was thinking of doing this is because it turns out to help
> performance to have map in scheme, at this point; or at least not hurt
> it, and things will get better when we grow an optimizer.
Yes, and I think we can keep rewriting SRFI-1 in Scheme, even in 2.0.
> So I implemented map in Scheme, with circularity detection and all, only
> to find strange errors in the ecmascript compiler (!). Turns out those
> errors happened when loading goops, because it tried to extend a
> primitive generic, but map wasn't a primitive any more, and instead of
> failing nicely it corrupted memory.
Ooh, interesting. :-)
Thanks,
Ludo’.
next prev parent reply other threads:[~2011-05-05 20:21 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-05-05 15:24 early termination for `map' Andy Wingo
2011-05-05 15:56 ` Noah Lavine
2011-05-05 16:26 ` Ludovic Courtès
2011-05-05 18:40 ` Andy Wingo
2011-05-05 20:21 ` Ludovic Courtès [this message]
2011-05-05 21:12 ` Andy Wingo
2011-05-06 15:41 ` Ludovic Courtès
2011-05-08 15:05 ` ‘map’ and ‘for-each’ written in Scheme Ludovic Courtès
2011-05-08 15:31 ` Andy Wingo
2011-05-05 18:27 ` early termination for `map' Andy Wingo
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