State Machines for Interaction

Haskell invariably offers a challenge when writing interactive code, since (unlike for most pure functional code), there aren't many nice abstractions available in the hierarchical libraries for doing interactiony things. One of the abstractions I'd like to investigate for handling input in Moing are state machines: a state machine consumes Gdk events, produces higher-level events which it feeds to another layer of state machines, and so on.