arrows- Arrow classes and transformers

Portabilitynon-portable (multi-parameter type classes)
Safe HaskellNone



Arrow transformer that adds a read-only state (i.e. an environment).



newtype ReaderArrow r a b c Source

An arrow type that augments an existing arrow with a read-only state (or environment). The ArrowReader class contains the operations on this state.


ReaderArrow (a (b, r) c) 


(Arrow (ReaderArrow r a), ArrowError ex a) => ArrowError ex (ReaderArrow r a) 
(Monoid s, Arrow (ReaderArrow r a), ArrowWriter s a) => ArrowWriter s (ReaderArrow r a) 
(Arrow (ReaderArrow r a), ArrowState s a) => ArrowState s (ReaderArrow r a) 
(Arrow (ReaderArrow r a), Arrow a) => ArrowReader r (ReaderArrow r a) 
(ArrowReader r (ReaderArrow r a), Arrow a) => ArrowAddReader r (ReaderArrow r a) a 
(ArrowError ex (ReaderArrow r a), Arrow (ReaderArrow r a'), ArrowAddError ex a a') => ArrowAddError ex (ReaderArrow r a) (ReaderArrow r a') 
(ArrowWriter s (ReaderArrow r a), Arrow (ReaderArrow r a'), ArrowAddWriter s a a') => ArrowAddWriter s (ReaderArrow r a) (ReaderArrow r a') 
(ArrowState s (ReaderArrow r a), Arrow (ReaderArrow r a'), ArrowAddState s a a') => ArrowAddState s (ReaderArrow r a) (ReaderArrow r a') 
(Arrow (ReaderArrow r a), Arrow a) => ArrowTransformer (ReaderArrow r) a 
(Category (ReaderArrow r a), Arrow a) => Arrow (ReaderArrow r a) 
(Arrow (ReaderArrow r a), ArrowZero a) => ArrowZero (ReaderArrow r a) 
(ArrowZero (ReaderArrow r a), ArrowPlus a) => ArrowPlus (ReaderArrow r a) 
(Arrow (ReaderArrow r a), ArrowChoice a) => ArrowChoice (ReaderArrow r a) 
(Arrow (ReaderArrow r a), ArrowApply a) => ArrowApply (ReaderArrow r a) 
(Arrow (ReaderArrow r a), ArrowLoop a) => ArrowLoop (ReaderArrow r a) 
Arrow a => Category (ReaderArrow r a) 
(ArrowLoop (ReaderArrow r a), ArrowCircuit a) => ArrowCircuit (ReaderArrow r a) 
Arrow a => Functor (ReaderArrow r a b) 
(Functor (ReaderArrow r a b), Arrow a) => Applicative (ReaderArrow r a b) 
(Applicative (ReaderArrow r a b), ArrowPlus a) => Alternative (ReaderArrow r a b) 
ArrowPlus a => Monoid (ReaderArrow r a b c) 

runReader :: Arrow a => ReaderArrow r a e b -> a (e, r) bSource

Encapsulation of a state-reading computation, taking a value for the state.

Typical usage in arrow notation:

	proc p -> ...
		(|runReader cmd|) env

class (ArrowReader r a, Arrow a') => ArrowAddReader r a a' | a -> a' whereSource

Adding a ReaderArrow 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 lift method of the ArrowTransformer class, or remove a state transformer from the top of the stack using the runReader encapsulation operator. The methods of this class add and remove state transformers anywhere in the stack. In the instance

	instance Arrow a => ArrowAddReader r (ArrowReader r a) a

they are equivalent to lift and runReader respectively. Instances are lifted through other transformers with

	instance ArrowAddReader r a a' =>
		ArrowAddReader r (FooArrow a) (FooArrow a')


liftReader :: a' e b -> a e bSource

Lift a computation from an arrow to one with an added environment.

Typical usage in arrow notation:

	proc p -> ...
		(|liftReader cmd|)

elimReader :: a e b -> a' (e, r) bSource

Elimination of a state reader from a computation, taking a value for the state.

Typical usage in arrow notation:

	proc p -> ...
		(|elimReader cmd|) env