2010/11/3 John Szakmeister <j...@szakmeister.net>:
> I'm sorry... I don't quite understand this explanation. Do you mean
> that reduce is realizing the entire list all at once? I would think
> it would grab an element one at a time. Sorry for the stupid
> question, but there's something subtle here that I'm not
> understanding.
>
>> user=> (reduce #(doall (map + %1 %2)) (partition 5 (range 1e6)))
>> (99999500000 99999700000 99999900000 100000100000 100000300000)
>
> Is it because of the way the lazy sequence is being generated? Would
> different implementations of partition or range do better?
>
> Thanks in advance!
>
> -John
I think the problem is that this reduction will build an expression like this:
(map + ... (map + ... (map + ... (map + ... <one million nesting levels>))))
When clojure tries to realize an element of the resulting lazy seq,
every level will result in a nested method call, which will eventually
blow the stack.
// raek
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