Aditya: Not quite, because I'm actually looking to extract values from a functor (Maybe) with a default. Stephen: Thanks, I'll take a look at those. I do have a need for it. I'm writing a very similar library to Yampa. (I would be patching Yampa, but the code is a mess, so I decided to try starting from scratch.) Basically, I have a signal processing loop, where values are passed updated with a Maybe, representing whether there is or is not a change to the value. I could use a single Maybe around the whole thing, but that would require then re-updating a potentially large structure entirely. I want to be able to build a combinator that can combine two signal-fetching actions into a larger one: IO (Maybe a) -> IO (...) -> IO (Maybe a, (...)) and then an action that could, given the previous value: (a, (...)) update any places in this chain of pairs where the Maybe is not Nothing. Jake: I'd prefer to not have to define class instances for the types. It would get tedious and awkward quickly. (See above for a description of what I'm looking for.) -- Edward Amsden Undergraduate Computer Science Rochester Institute of Technology www.edwardamsden.com