[richhickey]

> and there's no parallel fold.

When working up from the bottom it might seem that this is just manual stream/list fusion. But the parallelism is the key prize. We need to stop defining map/filter etc in terms of lists/sequences, and, once we do, there is nothing to fuse, no streams/thunks to avoid allocating etc, because they were never essential in the first place, just an artifact of the history of FP and its early emphasis on lists and recursion.

[skew]

Yes, foldr/build is almost exactly reducibles, but not foldables.

Iterators do nothing for parallelism either.