Ryan Ingram wrote:
More FRP stuff: a new type for Future that came to me in an
inspiration this morning. But it's ugly and I need someone with
better theoretical underpinnings than me to tell me what I've really
built :)
data Future t a = Known t a | Unknown (t -> IO (STM (Maybe (Future t a))))
This is a composition of (applicative) functors. Not sure whether this
helps from the theoretical side, but it can be used to considerably
shorten your code:
type Tower t b = t -> IO (STM (Maybe b))
fmap4 :: (a -> b) -> Tower a -> Tower b
fmap4 f = fmap . fmap . fmap . fmap $ f
delayF :: Ord t => t -> Future t a -> Future t a
delayF t0 (Known t a) = Known (max t0 t) a
delayF t0 (Unknown f) = Unknown $ fmap4 (delayF0 t0) f
instance (Ord t, Bounded t) => Monad (Future t) where
return = Known minBound
Known t a >>= g = delayF t (g a)
Unknown f >>= g = Unknown $ fmap4 (>>= g) f
Regards,
apfelmus
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