On Wed, Apr 1, 2015 at 2:17 PM, Tassilo Horn <t...@gnu.org> wrote:
> Alex Miller <a...@puredanger.com> writes:
>
> Hi Alex,
>
> > - Eduction is no longer Seqable and thus the return from eduction is not
> > seqable (but it is reducible and iterable). You can use iterator-seq to
> get a
> > chunked seq over the top if you need one.
>
> Really?
>
> user> *clojure-version*
> {:major 1, :minor 7, :incremental 0, :qualifier "alpha6"}
> user> (seq (eduction (map inc) (range 10)))
> (1 2 3 4 5 6 7 8 9 10)
>
Yep. :)
user=> (supers (class (eduction (map inc) (range 10))))
#{clojure.lang.Sequential java.lang.Object java.lang.Iterable
clojure.lang.IReduceInit clojure.lang.IType}
However, seq checks for Iterable and will automatically use iterator-seq to
produce a seq from an Iterable, which is what's happening here.
See:
https://github.com/clojure/clojure/blob/master/src/jvm/clojure/lang/RT.java#L517
> - There are lots of performance implications due to those changes and
> > I would recommend re-testing any perf test related to sequence or
> > eduction on alpha6 to get a fresh picture as anything pre-alpha6 is
> > not comparable.
>
> My observations are all based on today's experience with alpha6. :-)
>
> > - eduction now takes multiple transformations, not just one, and
> > composes them. This is designed for mechanical rewriting (hello tool
> > developers!!) of ->> chains like this:
> >
> > (->> s (interpose 5) (partition-all 2))
> >
> > to this:
> >
> > (->> s (eduction (interpose 5) (partition-all 2)))
>
> Ah, that's sensible.
>
> > The general idea is that eduction is best when the result will be
> > completely consumed in a reducible context. Any case of reusing the
> > result will likely be better served by sequence which can cache and
> > reuse the answer.
>
> Yes, that's what I guessed. But at least when I tested replacing
> sequence with eduction at exactly these places () the result has been a
> slight slowdown instead of a speedup. But that might have been
> accidental as it is hard to do measurements with real-world code where a
> 5% slowdown/speedup might be the reason of something completely
> unrelated.
>
Are you including the cost of realizing the elements? Comparing this stuff
well is hard, or at least I had a hard time thinking through all the
nuances. From what I've looked at, I think the alpha6 changes have made
things slightly worse for sequence with transformations and somewhat better
for eductions used in a reducible or sequence context.
>
> Bye,
> Tassilo
>
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