Streaming

Constructing a Stream on a base functor

construct :: (forall b. (f b -> b) -> (m b -> b) -> (r -> b) -> b) -> Stream f m r

Reflect a church-encoded stream; cp. GHC.Exts.build

unfold :: (Monad m, Functor f) => (s -> m (Either r (f s))) -> s -> Stream f m r

Build a Stream by unfolding steps starting from a seed.

unfold inspect = id -- modulo the quotient we work with
unfold Pipes.next :: Monad m => Producer a m r -> Stream ((,) a) m r
unfold (curry (:>) . Pipes.next) :: Monad m => Producer a m r -> Stream (Of a) m r

for :: (Monad m, Functor f) => Stream (Of a) m r -> (a -> Stream f m x) -> Stream f m r

for replaces each element of a stream with an associated stream. Note that the associated stream may layer any functor.

Transforming streams

maps :: (Monad m, Functor f) => (forall x. f x -> g x) -> Stream f m r -> Stream g m r

Map layers of one functor to another with a natural transformation

maps' :: (Monad m, Functor f) => (forall x. f x -> m (a, x)) -> Stream f m r -> Stream (Of a) m r

Map free layers of a functor to a corresponding stream of individual elements. This simplifies the use of folds marked with a ''' in Streaming.Prelude

maps' sum' :: (Monad m, Num a) => Stream (Stream (Of a) m) m r -> Stream (Of a) m r
maps' (Pipes.fold' (+) (0::Int) id) :: Monad m => Stream (Producer Int m) m r -> Stream (Of Int) m r

mapsM :: (Monad m, Functor f) => (forall x. f x -> m (g x)) -> Stream f m r -> Stream g m r

Map layers of one functor to another with a transformation involving the base monad

Inspecting a stream

inspect :: (Functor f, Monad m) => Stream f m r -> m (Either r (f (Stream f m r)))

Inspect the first stage of a freely layered sequence. Compare Pipes.next and the replica Streaming.Prelude.next. This is the uncons for the general unfold.

unfold inspect = id
Streaming.Prelude.unfoldr StreamingPrelude.next = id

Eliminating a Stream

destroy :: (Functor f, Monad m) => Stream f m r -> (f b -> b) -> (m b -> b) -> (r -> b) -> b

Map a stream to its church encoding; compare list foldr

intercalates :: (Monad m, Monad (t m), MonadTrans t) => t m a -> Stream (t m) m b -> t m b

concats :: (MonadTrans t, Monad (t m), Monad m) => Stream (t m) m a -> t m a

iterTM :: (Functor f, Monad m, MonadTrans t, Monad (t m)) => (f (t m a) -> t m a) -> Stream f m a -> t m a

iterT :: (Functor f, Monad m) => (f (m a) -> m a) -> Stream f m a -> m a

Splitting and joining Streams

split :: (Monad m, Functor f) => Int -> Stream f m r -> Stream f m (Stream f m r)

chunksOf :: (Monad m, Functor f) => Int -> Stream f m r -> Stream (Stream f m) m r

concats :: (MonadTrans t, Monad (t m), Monad m) => Stream (t m) m a -> t m a

Types

data Stream f m r

Stream data type is equivalent to FreeT and can represent any effectful succession of steps, where the steps are specified by the first functor parameter.

data Stream f m r = Step !(f (Stream f m r)) | Delay (m (Stream f m r)) | Return r

The producer concept uses the simple functor (a,_) - or the stricter Of a _ . Then the news at each step or layer is just: an individual item of type a. Since Stream (Of a) m r is equivalent to Pipe.Producer a m r, much of the pipes Prelude can easily be mirrored in a streaming Prelude. Similarly, a simple Consumer a m r or Parser a m r concept arises when the base functor is (a -> _) . Stream ((->) input) m result consumes input until it returns a result.

To avoid breaking reasoning principles, the constructors should not be used directly. A pattern-match should go by way of inspect - or, in the producer case, next The constructors are exported by the Internal module.

Instances

Functor f => MFunctor (Stream f)

Functor f => MonadTrans (Stream f)

(Functor f, Monad m) => Monad (Stream f m)

(Functor f, Monad m) => Functor (Stream f m)

(Functor f, Monad m) => Applicative (Stream f m)

(MonadIO m, Functor f) => MonadIO (Stream f m)

(Eq r, Eq (m (Stream f m r)), Eq (f (Stream f m r))) => Eq (Stream f m r)

(Typeable (* -> *) f, Typeable (* -> *) m, Data r, Data (m (Stream f m r)), Data (f (Stream f m r))) => Data (Stream f m r)

(Show r, Show (m (Stream f m r)), Show (f (Stream f m r))) => Show (Stream f m r)

data Of a b

A left-strict pair; the base functor for streams of individual elements.

Constructors

!a :> b infixr 4

Instances

Functor (Of a)

Foldable (Of a)

Traversable (Of a)

(Eq a, Eq b) => Eq (Of a b)

(Data a, Data b) => Data (Of a b)

(Ord a, Ord b) => Ord (Of a b)

(Read a, Read b) => Read (Of a b)

(Show a, Show b) => Show (Of a b)

lazily :: Of a b -> (a, b)

strictly :: (a, b) -> Of a b

re-exports

class MFunctor t where

A functor in the category of monads, using hoist as the analog of fmap:

hoist (f . g) = hoist f . hoist g

hoist id = id

Methods

hoist :: Monad m => (forall a. m a -> n a) -> t m b -> t n b

Lift a monad morphism from m to n into a monad morphism from (t m) to (t n)

Instances

MFunctor ListT

MFunctor Backwards

MFunctor MaybeT

MFunctor IdentityT

MFunctor Lift

MFunctor (ReaderT r)

MFunctor (StateT s)

MFunctor (StateT s)

MFunctor (ExceptT e)

MFunctor (ErrorT e)

MFunctor (WriterT w)

MFunctor (WriterT w)

MFunctor (Product f)

Functor f => MFunctor (Compose f)

Functor f => MFunctor (Stream f)

MFunctor (RWST r w s)

MFunctor (RWST r w s)

class MonadTrans t where

The class of monad transformers. Instances should satisfy the following laws, which state that lift is a monad transformation:

• lift . return = return

• lift (m >>= f) = lift m >>= (lift . f)

Methods

lift :: Monad m => m a -> t m a

Lift a computation from the argument monad to the constructed monad.

Instances

MonadTrans ListT

MonadTrans MaybeT

MonadTrans IdentityT

MonadTrans (ReaderT r)

MonadTrans (StateT s)

MonadTrans (StateT s)

MonadTrans (ExceptT e)

Error e => MonadTrans (ErrorT e)

Monoid w => MonadTrans (WriterT w)

Monoid w => MonadTrans (WriterT w)

Functor f => MonadTrans (Stream f)

Monoid w => MonadTrans (RWST r w s)

Monoid w => MonadTrans (RWST r w s)