Just another comment on the topic of data structures.

I think it would be nice if Hashtbl and Map provided a compatible sub-API 
written in continuation passing style so that application writers can 
functorize their code over the low-level implementation that is used.

The trade-offs involved in choosing between Hashtbl and Map are non-trivial 
and it would be nice if unsure programmers could adopt a style that made it 
easy to switch between data structures.

-- 
Dr Jon D Harrop, Flying Frog Consultancy Ltd.
The OCaml Journal
http://www.ffconsultancy.com/products/ocaml_journal/?e