Re: [Haskell-cafe] Polymorphic function over pairs of maybes.

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.

Sounds like you want a generic diff: http://hackage.haskell.org/package/gdiff-1.0 Cheers, Sterl