Functional processing of Scala streams without OutOfMemory errors

Question

Is it possible to apply functional programming to Scala streams such that the stream is processed sequentially, but the already processed part of the stream can be garbage c

Answer 1

As it turns out, this is a bug in the current implementation of reduceLeft. The problem is that reduceLeft calls foldLeft, and thus the stackframe of reduceLeft holds a reference to the head of the stream during the whole call. foldLeft uses tail-recursion to avoid this problem. Compare:

(1 to 10000000).toStream.foldLeft(0)(_+_)
(1 to 10000000).toStream.reduceLeft(_+_)

These are semantically equivalent. In Scala version 2.8.0 the call to foldLeft works, but the call to reduceLeft throws an OutOfMemory. If reduceLeft would do its own work, this problem would not occur.