Damn, just noticed a small mistake in the macro: I use the original buffer,
not the duplicated one. Here's the correct version:
(defmacro buffer-reduce [b f val]
`(let [b# (.duplicate ~b)]
(loop [remaining# (.remaining b#)
result# ~val]
(if (zero? remaining#)
result#
(recur (dec remaining#) (~f result# (.get b#)))))))
(extend-protocol clojure.core.protocols/CollReduce
java.nio.ByteBuffer
(coll-reduce [b f] (coll-reduce b f (f)))
(coll-reduce [b f val] (buffer-reduce b f val))
java.nio.LongBuffer
(coll-reduce [b f] (coll-reduce b f (f)))
(coll-reduce [b f val] (buffer-reduce b f val))
; ... other kinds of buffer ...
)
Sorry for that.
On Thursday, October 18, 2012 6:50:07 PM UTC-3, Bruno França dos Reis wrote:
>
> Hello!
>
> I've recently started playing with Clojure, and a couple of days ago I've
> been pointed to Reducers in Clojure 1.5 after a discussion on #clojure at
> Freenode.
>
> I've read Rich's posts announcing the Reducers library, and he says that
> there's a ***lack of reducible IO sources***. I'm working on a project
> that in which I analyze lots of data (from huge files on disk), and I'm
> frequently doing "reduce" operations on it. I began by writing a custom
> sequence, that after I transformed in a custom reducible collection. But
> I've just noticed that I could encapsulate it on a kind of reducible IO
> source.
>
> I'm writing this message to share the code I wrote relating to reducible
> IO sources, if anybody sees any use for it. The idea is to make the ***NIO
> Buffers reducible***, so that you can open huge files as **memory mapped
> files**, which are instances of `ByteBuffer`. You can then obtain
> instances of other buffers, say, `LongBuffer` (which is what I'm using on
> my current project), which are also reducible:
>
> (defmacro buffer-reduce [b f val]
> `(let [b# (.duplicate ~b)]
> (loop [remaining# (.remaining b#)
> result# ~val]
> (if (zero? remaining#)
> result#
> (recur (dec remaining#) (~f result# (.get ~b)))))))
>
> (extend-protocol clojure.core.protocols/CollReduce
> java.nio.ByteBuffer
> (coll-reduce [b f] (coll-reduce b f (f)))
> (coll-reduce [b f val] (buffer-reduce b f val))
>
> java.nio.LongBuffer
> (coll-reduce [b f] (coll-reduce b f (f)))
> (coll-reduce [b f val] (buffer-reduce b f val))
>
> ; ... other kinds of buffer ...
> )
>
>
> Hope this might be useful for someone.
>
> Bruno
>
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