Control.Arrow.Transformer.State

An arrow transformer that adds a modifiable state, based of section 9 of Generalising Monads to Arrows, by John Hughes, Science of Computer Programming 37:67-111, May 2000.

Documentation

newtype StateArrow s a b c

An arrow type that augments an existing arrow with a modifiable state. The ArrowState class contains the operations on this state.

Constructors

StateArrow (a (b, s) (c, s))

Instances

ArrowError ex a => ArrowError ex (StateArrow s a)

Methods

raise :: StateArrow s a ex b

handle :: StateArrow s a e b -> StateArrow s a (e, ex) b -> StateArrow s a e b

tryInUnless :: StateArrow s a e b -> StateArrow s a (e, b) c -> StateArrow s a (e, ex) c -> StateArrow s a e c

newError :: StateArrow s a e b -> StateArrow s a e (Either ex b)

ArrowWriter w a => ArrowWriter w (StateArrow s a)

Methods

write :: StateArrow s a w ()

newWriter :: StateArrow s a e b -> StateArrow s a e (b, w)

Arrow a => ArrowState s (StateArrow s a)

Methods

fetch :: StateArrow s a e s

store :: StateArrow s a s ()

ArrowReader r a => ArrowReader r (StateArrow s a)

Methods

readState :: StateArrow s a b r

newReader :: StateArrow s a e b -> StateArrow s a (e, r) b

Arrow a => ArrowAddState s (StateArrow s a) a

Methods

liftState :: a e b -> StateArrow s a e b

elimState :: StateArrow s a e b -> a (e, s) (b, s)

ArrowAddError ex a a' => ArrowAddError ex (StateArrow s a) (StateArrow s a')

Methods

liftError :: StateArrow s a' e b -> StateArrow s a e b

elimError :: StateArrow s a e b -> StateArrow s a' (e, ex) b -> StateArrow s a' e b

ArrowAddWriter w a a' => ArrowAddWriter w (StateArrow s a) (StateArrow s a')

Methods

liftWriter :: StateArrow s a' e b -> StateArrow s a e b

elimWriter :: StateArrow s a e b -> StateArrow s a' e (b, w)

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

Methods

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

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

Arrow a => ArrowTransformer (StateArrow s) a

Methods

lift :: a b c -> StateArrow s a b c

Category * a => Category * (StateArrow s a)

Methods

id :: cat a a

(.) :: cat b c -> cat a b -> cat a c

Arrow a => Arrow (StateArrow s a)

Methods

arr :: (b -> c) -> StateArrow s a b c

first :: StateArrow s a b c -> StateArrow s a (b, d) (c, d)

second :: StateArrow s a b c -> StateArrow s a (d, b) (d, c)

(***) :: StateArrow s a b c -> StateArrow s a b' c' -> StateArrow s a (b, b') (c, c')

(&&&) :: StateArrow s a b c -> StateArrow s a b c' -> StateArrow s a b (c, c')

ArrowZero a => ArrowZero (StateArrow s a)

Methods

zeroArrow :: StateArrow s a b c

ArrowPlus a => ArrowPlus (StateArrow s a)

Methods

(<+>) :: StateArrow s a b c -> StateArrow s a b c -> StateArrow s a b c

ArrowChoice a => ArrowChoice (StateArrow s a)

Methods

left :: StateArrow s a b c -> StateArrow s a (Either b d) (Either c d)

right :: StateArrow s a b c -> StateArrow s a (Either d b) (Either d c)

(+++) :: StateArrow s a b c -> StateArrow s a b' c' -> StateArrow s a (Either b b') (Either c c')

(|||) :: StateArrow s a b d -> StateArrow s a c d -> StateArrow s a (Either b c) d

ArrowApply a => ArrowApply (StateArrow s a)

Methods

app :: StateArrow s a (StateArrow s a b c, b) c

ArrowLoop a => ArrowLoop (StateArrow s a)

Methods

loop :: StateArrow s a (b, d) (c, d) -> StateArrow s a b c

ArrowCircuit a => ArrowCircuit (StateArrow s a)

Methods

delay :: b -> StateArrow s a b b

Arrow a => Functor (StateArrow s a b)

Methods

fmap :: (a -> b) -> StateArrow s a b a -> StateArrow s a b b

(<$) :: a -> StateArrow s a b b -> StateArrow s a b a

Arrow a => Applicative (StateArrow s a b)

Methods

pure :: a -> StateArrow s a b a

(<*>) :: StateArrow s a b (a -> b) -> StateArrow s a b a -> StateArrow s a b b

liftA2 :: (a -> b -> c) -> StateArrow s a b a -> StateArrow s a b b -> StateArrow s a b c

(*>) :: StateArrow s a b a -> StateArrow s a b b -> StateArrow s a b b

(<*) :: StateArrow s a b a -> StateArrow s a b b -> StateArrow s a b a

ArrowPlus a => Alternative (StateArrow s a b)

Methods

empty :: StateArrow s a b a

(<|>) :: StateArrow s a b a -> StateArrow s a b a -> StateArrow s a b a

some :: StateArrow s a b a -> StateArrow s a b [a]

many :: StateArrow s a b a -> StateArrow s a b [a]

ArrowPlus a => Semigroup (StateArrow s a b c)

Methods

(<>) :: StateArrow s a b c -> StateArrow s a b c -> StateArrow s a b c

sconcat :: NonEmpty (StateArrow s a b c) -> StateArrow s a b c

stimes :: Integral b => b -> StateArrow s a b c -> StateArrow s a b c

ArrowPlus a => Monoid (StateArrow s a b c)

Methods

mempty :: StateArrow s a b c

mappend :: StateArrow s a b c -> StateArrow s a b c -> StateArrow s a b c

mconcat :: [StateArrow s a b c] -> StateArrow s a b c

runState :: Arrow a => StateArrow s a e b -> a (e, s) (b, s)

Encapsulation of a state-using computation, exposing the initial and final states.

Typical usage in arrow notation:

   proc p -> do
       ...
       (result, final_state) <- (|runState cmd|) init_state

class (ArrowState s a, Arrow a') => ArrowAddState s a a' | a -> a' where

Adding a StateArrow 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 runState encapsulation operator. The methods of this class add and remove state transformers anywhere in the stack. In the instance

   instance Arrow a => ArrowAddState s (ArrowState s a) a

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

   instance ArrowAddState s a a' =>
       ArrowAddState s (FooArrow a) (FooArrow a')

Minimal complete definition

liftState, elimState

Methods

liftState :: a' e b -> a e b

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

Typical usage in arrow notation:

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

elimState :: a e b -> a' (e, s) (b, s)

Elimination of a state transformer from a computation, exposing the initial and final states.

Typical usage in arrow notation:

   proc p -> do
       ...
       (result, final_state) <- (|elimState cmd|) init_state

Instances

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

Methods

liftState :: Automaton a' e b -> Automaton a e b

elimState :: Automaton a e b -> Automaton a' (e, r) (b, r)

Arrow a => ArrowAddState s (StateArrow s a) a

Methods

liftState :: a e b -> StateArrow s a e b

elimState :: StateArrow s a e b -> a (e, s) (b, s)

(ArrowAddState s a a', ArrowChoice a, ArrowChoice a') => ArrowAddState s (ErrorArrow ex a) (ErrorArrow ex a')

Methods

liftState :: ErrorArrow ex a' e b -> ErrorArrow ex a e b

elimState :: ErrorArrow ex a e b -> ErrorArrow ex a' (e, s) (b, s)

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

Methods

liftState :: ReaderArrow r a' e b -> ReaderArrow r a e b

elimState :: ReaderArrow r a e b -> ReaderArrow r a' (e, s) (b, s)

(ArrowAddState s a a', Applicative f) => ArrowAddState s (StaticArrow f a) (StaticArrow f a')

Methods

liftState :: StaticArrow f a' e b -> StaticArrow f a e b

elimState :: StaticArrow f a e b -> StaticArrow f a' (e, s) (b, s)

(ArrowAddState s a a', Monoid w) => ArrowAddState s (WriterArrow w a) (WriterArrow w a')

Methods

liftState :: WriterArrow w a' e b -> WriterArrow w a e b

elimState :: WriterArrow w a e b -> WriterArrow w a' (e, s) (b, s)