Control.Arrow.Transformer.Reader

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

Documentation

data ReaderArrow r a b c

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

Instances

ArrowError ex a => ArrowError ex (ReaderArrow r a)

ArrowWriter s a => ArrowWriter s (ReaderArrow r a)

ArrowState s a => ArrowState s (ReaderArrow r a)

Arrow a => ArrowReader r (ReaderArrow r a)

Arrow a => ArrowAddReader r (ReaderArrow r a) a

ArrowAddError ex a a' => ArrowAddError ex (ReaderArrow r a) (ReaderArrow r a')

ArrowAddWriter s a a' => ArrowAddWriter s (ReaderArrow r a) (ReaderArrow r a')

ArrowAddState s a a' => ArrowAddState s (ReaderArrow r a) (ReaderArrow r a')

Arrow a => ArrowTransformer (ReaderArrow r) a

Arrow a => Arrow (ReaderArrow r a)

ArrowZero a => ArrowZero (ReaderArrow r a)

ArrowPlus a => ArrowPlus (ReaderArrow r a)

ArrowChoice a => ArrowChoice (ReaderArrow r a)

ArrowApply a => ArrowApply (ReaderArrow r a)

ArrowLoop a => ArrowLoop (ReaderArrow r a)

Arrow a => Category (ReaderArrow r a)

ArrowCircuit a => ArrowCircuit (ReaderArrow r a)

Arrow a => Functor (ReaderArrow r a b)

Arrow a => 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) b

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' where

Adding a Control.Arrow.Transformer.Reader.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 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.Reader.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 Control.Arrow.Transformer.lift and Control.Arrow.Transformer.Reader.runReader respectively. Instances are lifted through other transformers with

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

Methods

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

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) b

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

Typical usage in arrow notation:

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

Instances

ArrowAddReader r a a' => ArrowAddReader r (Automaton a) (Automaton a')

Arrow a => ArrowAddReader r (ReaderArrow r a) a

(ArrowAddReader r a a', ArrowChoice a, ArrowChoice a') => ArrowAddReader r (ErrorArrow ex a) (ErrorArrow ex a')

ArrowAddReader r a a' => ArrowAddReader r (StateArrow s a) (StateArrow s a')

(ArrowAddReader r a a', Applicative f) => ArrowAddReader r (StaticArrow f a) (StaticArrow f a')

(ArrowAddReader r a a', Monoid w) => ArrowAddReader r (WriterArrow w a) (WriterArrow w a')