On Tue, Nov 3, 2009 at 11:51 PM, Mark Engelberg
<mark.engelb...@gmail.com> wrote:
>
> Clojure's built-in "range" function (last time I looked) essentially
> produces an uncached sequence. And that makes a lot of sense.
'range' has since changed and now produces a chunked lazy seq
(master branch post-1.0).
> Producing the next value in a range on-demand is way more efficient
> and practical than caching those values. I think that Clojure
> programmers should have an easy way to make similarly uncached
> sequences if that's what they really want/need.
This can be done by implementing the ISeq interface, today with
proxy, in the future with newnew/reify/deftype/etc.
(defn incs [i]
(proxy [clojure.lang.ISeq] []
(seq [] this)
(first [] i)
(next [] (incs (inc i)))))
user=> (let [r (range 1e9)] [(first r) (last r)])
java.lang.OutOfMemoryError: GC overhead limit exceeded (NO_SOURCE_FILE:0)
user=> (let [r (incs 10)] [(first r) (nth r 1e9)])
[10 1000000010]
Both those examples retain the head, but since 'incs' isn't
a lazy-seq, the intermediate values can be garbage-collected.
Note the difference between the seq abstraction and the lazy-seq
implementation.
--Chouser
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