I'd like to design a function that splits behaviors based on the time of an event occurrence. Here is the type signature: splitB_ :: Behavior a -> Behavior a -> Event () -> Event (Behavior a) An example in semantics: splitB_ (const 1) (const 2) [(0,()), (1,())] => [ (0, (\t -> if t <= 0 then 1 else 2)) , (1, (\t -> if t <= 1 then 1 else 2)) ] Operationally, the implementation must avoid traversing all of the second behavior's reactive's steps at every occurrence of the event, so the following implementation isn't going to win anyone a beer: splitB_ :: Behavior a -> Behavior a -> Event () -> Event (Behavior a) splitB_ bLeft bRight e = fmap f (withTimeE_ e) where f ot = iffB (fmap (ot >=) time) bLeft bRight iffB :: Behavior Bool -> Behavior a -> Behavior a -> Behavior a iffB = liftA3 iff iff a b c = if a then b else c Thanks! David -- David Sankel Sankel Software