First class modules in OCaml 3.12: What kinds of things will they make easier (or possible)?

Question

I've heard that "first class modules" are coming in OCaml 3.12. What advantages will they offer? What kids of things will be easier? What problem are they trying to solve? A simple example would suffice.

Answer 1

Maybe a bit late, but the new paper First-class modules: hidden power and tantalizing promises is exactly on topic. It's a set of recipes/pearls around first-class modules, by Oleg Kiselyov (oleg) and Jeremy Yallop (author, for example, of the Deriving project).