Quick post to say that I've put my dabblings into Chris Okasaki's Purely Functional Data Structures book up as a github repo. I am picking and choosing what exercises and examples to code, with the goal being to slowly cover the whole book. Some concessions are made to fit the ideas into Erlang (like recursively calling an anonymous function), but overall I think the ideas fit nicely. There is a streams lib from Richard Carlsson that I found on the Erlang mailing list in the repo as well that I used for reference for a couple things in chapter 4. I stuck with my streams being represented either as an empty list  or [term() | fun()] with term() being the calculated value and fun() being the suspension function, instead of the tuple that Richard chose. After reading further in the thread, I understand why (don't confuse people that might use proper list functions on streams) but for my small examples, it was enough to use lists.