Last active
August 29, 2015 14:01
-
-
Save crdueck/6393f5464d2f99008764 to your computer and use it in GitHub Desktop.
Signal
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
import Control.Applicative | |
import Control.Monad | |
import Data.Monoid | |
data SignalT m a | |
= Skip (m (SignalT m a)) | |
| Emit a (m (SignalT m a)) | |
instance Monad m => Functor (SignalT m) where | |
fmap f = go | |
where go (Skip m) = Skip (liftM go m) | |
go (Emit a m) = Emit (f a) (liftM go m) | |
-- TODO | |
instance Monad m => Applicative (SignalT m) where | |
pure a = Emit a (return (pure a)) | |
sf <*> sx = go sf | |
where go (Skip m) = Skip (liftM go m) | |
go (Emit f m) = fmap f sx | |
-- TODO | |
instance Monad m => Monad (SignalT m) where | |
return = pure | |
s0 >>= f = go s0 | |
where go (Skip m) = Skip (liftM go m) | |
go (Emit a m) = f a | |
instance (Monad m, Monoid a) => Monoid (SignalT m a) where | |
mempty = never | |
Skip m `mappend` Skip n = Skip (liftM2 mappend m n) | |
Skip m `mappend` Emit a n = Emit a (liftM2 mappend m n) | |
Emit a m `mappend` Skip n = Emit a (liftM2 mappend m n) | |
Emit a m `mappend` Emit b n = Emit (a `mappend` b) (liftM2 mappend m n) | |
never :: Monad m => SignalT m a | |
never = Skip (return never) | |
once :: Monad m => a -> SignalT m a | |
once a = Emit a (return never) | |
always :: Monad m => a -> SignalT m a | |
always a = Emit a (return (always a)) | |
every :: Monad m => Int -> a -> SignalT m a | |
every n a = go n | |
where go 1 = Emit a (return (go n)) | |
go x = Skip (return (go (x - 1))) | |
delay :: Monad m => SignalT m a -> SignalT m a | |
delay = Skip . return | |
hold :: Monad m => SignalT m a -> SignalT m a | |
hold (Skip m) = Skip (m >>= return . hold) | |
hold (Emit a m) = always a | |
switch :: Monad m => SignalT m a -> SignalT m a -> SignalT m a | |
switch l r = go l | |
where go (Skip _) = r | |
go (Emit a m) = Emit a (m >>= return . go) | |
scan :: Monad m => (a -> b -> b) -> b -> SignalT m a -> SignalT m b | |
scan f = go | |
where go z (Skip m) = Skip (m >>= return . go z) | |
go z (Emit a m) = | |
let b = f a z in Emit b (m >>= return . go b) | |
toList :: Monad m => SignalT m a -> m [a] | |
toList (Skip m) = m >>= toList | |
toList (Emit a m) = m >>= toList >>= \xs -> return (a : xs) | |
--main = toList (always 'a') >>= print . take 10 | |
--main = toList ((+) <$> always 4 <*> always 5) >>= print . take 10 |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment