Hi Cam,
Your tests aren't testing the interesting part without a doall.
That said, my quick tests with doall show your approach faring even better. :-)
Also, I think what my-flatten does with Java arrays is intuitive (and the
current flatten not so much).
A patch that preserves the semantics of the existing flatten (except for
working with Java arrays) would be welcome.
Thanks!
Stu
> Another flatten thread! Sorry..
>
> Hello all, before I realized there was a flatten in the master branch
> (and before I looked at contrib) I wrote this pretty standard code:
>
> (defn my-flatten [coll]
> (lazy-seq
> (when-let [coll (seq coll)]
> (let [x (first coll)]
> (if (sequential? x)
> (concat (my-flatten x) (my-flatten (next coll)))
> (cons x (my-flatten (next coll))))))))
>
> (There's very similar versions on the boards. I'm not claiming this is
> anything amazing or unique.)
>
> It's not as elegant as what's in core, but in my micro benchmarks (ran
> on my laptop; 2.26 core 2 and 4gb ram) it seems to perform a bit
> better, _especially_ in the already flattened case. It behaves just
> like core/flatten except that it doesn't return an empty list when
> passed a map or set, it just returns whatever you gave it but with the
> top level converted to a seq. I'm pretty much a clojure noob, so are
> there any hidden detractors of this implementation as opposed to the
> version introduced in 1.2?
>
> Also, quick note, if you swap the call to sequential? with seqable?
> from contrib/core, it flattens maps and sets like you'd expect as
> well.
> Here is how it looks
> user=> (my-flatten #{1 {2 3} 4 [5 6 7 #{8 {9 10}}]})
> (1 2 3 4 5 6 7 9 10 8)
>
> And for the micro-benchmarks (using "sequential?"):
>
> user=> (time (dotimes [_ 1e7] (flatten [1 2 3 4])))
> "Elapsed time: 14,661.592 msecs"
> nil
>
> user=> (time (dotimes [_ 1e7] (my-flatten [1 2 3 4])))
> "Elapsed time: 922.268 msecs"
> nil
>
> user=> (time (dotimes [_ 1e7] (flatten [1 [2 [3 [4 [5 [6 [7 [8]
> [[[9]]] 10 [11] 12 [13 14 [15]]]]]]]]])))
> "Elapsed time: 18,147.959 msecs"
> nil
>
> user=> (time (dotimes [_ 1e7] (my-flatten [1 [2 [3 [4 [5 [6 [7 [8]
> [[[9]]] 10 [11] 12 [13 14 [15]]]]]]]]])))
> "Elapsed time: 6,088.914 msecs"
> nil
>
> user=> (time (dotimes [_ 1e7] (flatten [[1 2 3 4 5 6 7 8 9 10]])))
> "Elapsed time: 11,696.693 msecs"
> nil
>
> user=> (time (dotimes [_ 1e7] (my-flatten [[1 2 3 4 5 6 7 8 9 10]])))
> "Elapsed time: 1,533.983 msecs"
> nil
>
> Thoughts?
>
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