StreamT.hs

{-# LANGUAGE ApplicativeDo #-}
module StreamT where

-- base
import Control.Arrow

data StreamT m a = StreamT { unStreamT :: m (a, StreamT m a) }

instance Functor m => Functor (StreamT m) where
  fmap f = StreamT . fmap (f *** fmap f) . unStreamT

instance Applicative m => Applicative (StreamT m) where
  pure a = StreamT $ pure (a, pure a)
  fs <*> as = StreamT $ do
    (f, fs') <- unStreamT fs
    (a, as') <- unStreamT as
    pure (f a, fs' <*> as')