Another nice abuse of core.async is for the implementation of
multi-reducible collections. Here is the implementation of interleave
accepting/producing reducibles. Slower than lazy seqs, but hey, you can
feed it with any reducible coll. BTW anybody knows the status of multi
reducibles? Are they being worked on?
(defn interleave* [& colls]
(reify clojure.core.protocols.CollReduce
(coll-reduce [this f1]
(clojure.core.protocols/coll-reduce this f1 (f1)))
(coll-reduce [_ f1 init]
(let [NIL (Object.)
encode-nil #(if (nil? %) NIL %)
decode-nil #(if (identical? NIL %) nil %)
send-fn (fn [coll]
(let [c (chan)]
(thread (reduce (fn [r v] (>!! c (encode-nil v))) nil
coll)
(close! c))
c))
chans (doall (map send-fn colls))]
(loop [val init
s (cycle chans)]
(let [c (first s)
x (<!! c)]
(if-not (nil? x)
(let [x (decode-nil x)
ret (f1 val x)]
(if (reduced? ret)
@ret
(recur ret (rest s))))
val)))))))
(reduce + (clojure.core.reducers/take 100
(interleave* (range)
(clojure.core.reducers/map inc (range)))))
https://gist.github.com/wagjo/6335189
JW
On Sunday, August 25, 2013 7:47:14 PM UTC+2, Jozef Wagner wrote:
>
> Hi,
>
> A distinctive feature of reducers is that "reducing is a one-shot thing".
> The common understanding is that reducers are fast for cases where you want
> to process whole collection at once, but for infinite and lazy seqs, you
> have to use good old seqs.
>
> With core.async, it is now easy to create a transformation which produces
> lazy seq from any reducible collection.
>
> (defn lazy-seq*
> [reducible]
> (let [c (chan)
> NIL (Object.)
> encode-nil #(if (nil? %) NIL %)
> decode-nil #(if (identical? NIL %) nil %)]
> (thread
> (reduce (fn [r v] (>!! c (encode-nil v))) nil reducible)
> (close! c))
> (take-while (complement nil?) (repeatedly #(decode-nil (<!! c))))))
>
> (def s (lazy-seq* (clojure.core.reducers/map inc (range))))
>
> (first s)
>
> (take 100 s)
>
> This approach can be also extended to produce chunked seqs and chan buffer
> can also be used to further tune the performance.
>
> JW
>
>
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