Portability | non-portable (multi-parameter type classes) |
---|---|
Stability | experimental |
Maintainer | ross@soi.city.ac.uk |
Arrow transformer that adds a read-only state (i.e. an environment).
- data ReaderArrow r a b c
- runReader :: Arrow a => ReaderArrow r a e b -> a (e, r) b
- class (ArrowReader r a, Arrow a') => ArrowAddReader r a a' | a -> a' where
- liftReader :: a' e b -> a e b
- elimReader :: a e b -> a' (e, r) b
Documentation
data 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.
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 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')
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
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') |