Control.Comonad.Trans.Stream

The f-branching stream comonad, aka the cofree comonad for a Functor f.

Provided here as a comonad-transformer version of the 'ListT done right' monad transformer.

The Stream comonad

type Stream f = StreamT f Identity

Isomorphic to the definition:

 data Stream f a = a :< f (Stream f a)

stream :: a -> f (Stream f a) -> Stream f a

cons onto an f-branching stream

runStream :: Stream f a -> (a, f (Stream f a))

uncons from an f-branching stream

unfolds :: Functor f => (a -> (b, f a)) -> a -> Stream f b

unfold a stream from a seed.

The Stream comonad transformer

data StreamT f w a

The f-branching stream comonad transformer is a comonadic version of the "ListT done Right" monad transformer. You can extract the underlying comonadic value by using lower or runStream

Constructors

StreamT

Fields

runStreamT :: w (a, f (StreamT f w a))

Instances

Functor f => ComonadTrans (StreamT f)

Functor f => ComonadHoist (StreamT f)

(Functor w, Functor f) => Functor (StreamT f w)

(Foldable w, Foldable f) => Foldable (StreamT f w)

(Traversable w, Traversable f) => Traversable (StreamT f w)

(Comonad w, Functor f) => Comonad (StreamT f w)

(ComonadApply w, FunctorApply f) => FunctorApply (StreamT f w)

(ComonadApply w, FunctorApply f) => ComonadApply (StreamT f w)

Operations

tails :: Comonad w => StreamT f w a -> f (StreamT f w a)

unfoldsW :: (Comonad w, Functor f) => (w a -> (b, f a)) -> w a -> StreamT f w b