arrows-0.3: Arrow classes and transformersSource codeContentsIndex
Control.Arrow.Transformer.Stream
Portabilitynon-portable (multi-parameter type classes)
Stabilityexperimental
Maintainer[email protected]
Description
Arrow transformer lifting an arrow to streams.
Synopsis
data StreamArrow a b c
runStream :: ArrowLoop a => StreamArrow a (e, b) c -> a (e, Stream b) (Stream c)
type StreamMap = StreamArrow (->)
type StreamMapST s = StreamArrow (Kleisli (ST s))
runStreamST :: (forall s. StreamMapST s e c) -> StreamMap e c
class (ArrowCircuit a, Arrow a') => ArrowAddStream a a' | a -> a' where
liftStream :: a' e b -> a e b
elimStream :: a (e, b) c -> a' (e, Stream b) (Stream c)
Documentation
data StreamArrow a b c Source

Arrows between streams.

Note: lift is only a functor if *** in the underlying arrow is.

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runStream :: ArrowLoop a => StreamArrow a (e, b) c -> a (e, Stream b) (Stream c)Source

Run a stream processor on a stream of inputs, obtaining a stream of outputs.

Typical usage in arrow notation: 

	proc p -> do
		...
		ys <- (|runStream (\x -> ...)|) xs

Here xs refers to the input stream and x to individual elements of that stream. ys is bound to the output stream.

type StreamMap = StreamArrow (->)Source
Mappings of streams
type StreamMapST s = StreamArrow (Kleisli (ST s))Source

In-place state updates.

Note: this is an arrow type, and lift can be used to promote arrows from Kleisli (ST s): the resulting arrow updates the state for each stream element in turn, and as long as the final state in not required all is well. However, lift does not preserve composition, because this monad isn't commutative. In particular, a composition of lifts of state transformers will not work, as the second will require the final state of the first.

runStreamST :: (forall s. StreamMapST s e c) -> StreamMap e cSource
Encapsulate a local state.
class (ArrowCircuit a, Arrow a') => ArrowAddStream a a' | a -> a' whereSource

Adding a Control.Arrow.Transformer.Stream.StreamArrow to an arrow type, but not necessarily as the outer arrow transformer.

Typically a composite arrow type is built by applying a series of arrow transformer to a base arrow (usually either a function arrow or a Kleisli arrow. One can add a transformer to the top of this stack using the Control.Arrow.Transformer.lift method of the Control.Arrow.Transformer.ArrowTransformer class, or remove a state transformer from the top of the stack using the Control.Arrow.Transformer.Stream.runStream encapsulation operator. The methods of this class add and remove state transformers anywhere in the stack. In the instance 

	instance Arrow a => ArrowAddStream (ArrowStream a) a

they are equivalent to Control.Arrow.Transformer.lift and Control.Arrow.Transformer.Stream.runStream respectively. Instances are lifted through other transformers with 

	instance ArrowAddStream a a' =>
		ArrowAddStream (FooArrow a) (FooArrow a')
Methods
liftStream :: a' e b -> a e bSource
elimStream :: a (e, b) c -> a' (e, Stream b) (Stream c)Source
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