Thank you for another great technique and concept!.
I've been using reducers a lot lately and I've found that it is in some
cases better (performance, fold support) to wrap local state in the
intermediate result, rather than to keep it in an atom. See this *very*
simplified example for
comparison https://gist.github.com/wagjo/30000277f6923ac8d88f
;; state is kept in a ret
(deftype WrapState [ret n])
(deftype WrapTake [coll n]
CollReduce
(coll-reduce [this f init]
(let [init-state (->WrapState init n)
tf (fn [^WrapState state val]
(let [ret (.-ret state)
ni (dec (.-n state))
nret (f ret val)]
(cond (reduced? nret)
(reduced (->WrapState @nret nil))
(zero? ni)
(reduced (->WrapState nret nil))
:else (->WrapState nret ni))))
ret-state (coll-reduce coll tf init-state)]
(.-ret ^WrapState ret-state))))
;; state is kept in atom
(deftype AtomTake [coll n]
CollReduce
(coll-reduce [this f init]
(let [na (atom n)
tf (fn [ret val]
(swap! na dec)
(let [ni @na
nret (f ret val)]
(if (zero? ni)
(reduced nret)
nret)))]
(coll-reduce coll tf init))))
>From what I've understood from the transducers impl, it would no longer be
able to do such ret wrapping, am I right?
Best,
Jozef
On Wednesday, August 6, 2014 8:01:24 PM UTC+2, Rich Hickey wrote:
>
> I pushed today the initial work on transducers. I describe transducers
> briefly in this blog post:
>
> http://blog.cognitect.com/blog/2014/8/6/transducers-are-coming
>
> This work builds on the work done for reducers, bringing
> context-independent mapping, filtering etc to other areas, such as
> core.async.
>
> This is work in progress. We will be cutting alpha releases to help make
> it easier to start using core's transducers together with core.async's new
> support for them.
>
> I am very excited about this powerful technique and how we all might use
> it.
>
> Please have a look.
>
> Feedback welcome,
>
> Rich
>
>
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