[reactive] Re: Whoever implements splitB gets a virtual beer from me.

Replying to my own request: http://netsuperbrain.com/blog/posts/why-is-the-reactive-behavior-tutorial-ta... -- David Sankel On Thu, Nov 13, 2008 at 1:53 PM, David Sankel wrote:

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