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

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David Sankel
Sankel Software