[mjw]

Yep I figured this would probably not be very efficient.

About lazy sequences: sometimes you want to avoid the allocation of lots of intermediate cons cells when mapping/filtering/etc. The reducers framework for example manages to avoid this sort of cost when the data structure supports something faster than first/rest recursion. I'm interested in extending reducers to work nicely over large files and other sequences which don't fit in memory, and some kind of iterable or generator-like abstraction could play a useful role in this.

(Actual coroutine-based generators might not be necessary, but would allow for a neat outward-facing API)