Copyright	(c) Ross Paterson 2003
License	BSD-style (see the LICENSE file in the distribution)
Maintainer	R.Paterson@city.ac.uk
Stability	experimental
Portability	non-portable (multi-parameter type classes)
Safe Haskell	Safe
Language	Haskell98

Control.Arrow.Transformer.Writer

Description

Arrow transformer that adds accumulation of output.

Synopsis

Documentation

newtype WriterArrow w a b c Source #

An arrow type that augments an existing arrow with accumulating output. The ArrowWriter class contains the relevant operations.

Constructors

WriterArrow (a b (c, w))

Instances

(ArrowError ex a, Monoid w) => ArrowError ex (WriterArrow w a) Source #
Methods raise :: WriterArrow w a ex b Source # handle :: WriterArrow w a e b -> WriterArrow w a (e, ex) b -> WriterArrow w a e b Source # tryInUnless :: WriterArrow w a e b -> WriterArrow w a (e, b) c -> WriterArrow w a (e, ex) c -> WriterArrow w a e c Source # newError :: WriterArrow w a e b -> WriterArrow w a e (Either ex b) Source #
(Arrow a, Monoid w) => ArrowWriter w (WriterArrow w a) Source #
Methods write :: WriterArrow w a w () Source # newWriter :: WriterArrow w a e b -> WriterArrow w a e (b, w) Source #
(ArrowState s a, Monoid w) => ArrowState s (WriterArrow w a) Source #
Methods fetch :: WriterArrow w a e s Source # store :: WriterArrow w a s () Source #
(ArrowReader r a, Monoid w) => ArrowReader r (WriterArrow w a) Source #
Methods readState :: WriterArrow w a b r Source # newReader :: WriterArrow w a e b -> WriterArrow w a (e, r) b Source #
(Arrow a, Monoid w) => ArrowAddWriter w (WriterArrow w a) a Source #
Methods liftWriter :: a e b -> WriterArrow w a e b Source # elimWriter :: WriterArrow w a e b -> a e (b, w) Source #
(ArrowAddError ex a a', Monoid w) => ArrowAddError ex (WriterArrow w a) (WriterArrow w a') Source #
Methods liftError :: WriterArrow w a' e b -> WriterArrow w a e b Source # elimError :: WriterArrow w a e b -> WriterArrow w a' (e, ex) b -> WriterArrow w a' e b Source #
(ArrowAddReader r a a', Monoid w) => ArrowAddReader r (WriterArrow w a) (WriterArrow w a') Source #
Methods liftReader :: WriterArrow w a' e b -> WriterArrow w a e b Source # elimReader :: WriterArrow w a e b -> WriterArrow w a' (e, r) b Source #
(ArrowAddState s a a', Monoid w) => ArrowAddState s (WriterArrow w a) (WriterArrow w a') Source #
Methods liftState :: WriterArrow w a' e b -> WriterArrow w a e b Source # elimState :: WriterArrow w a e b -> WriterArrow w a' (e, s) (b, s) Source #
(Arrow a, Monoid w) => ArrowTransformer (WriterArrow w) a Source #
Methods lift :: a b c -> WriterArrow w a b c Source #
(Arrow a, Monoid w) => Category * (WriterArrow w a) Source #
Methods id :: cat a a # (.) :: cat b c -> cat a b -> cat a c #
(Arrow a, Monoid w) => Arrow (WriterArrow w a) Source #
Methods arr :: (b -> c) -> WriterArrow w a b c # first :: WriterArrow w a b c -> WriterArrow w a (b, d) (c, d) # second :: WriterArrow w a b c -> WriterArrow w a (d, b) (d, c) # (***) :: WriterArrow w a b c -> WriterArrow w a b' c' -> WriterArrow w a (b, b') (c, c') # (&&&) :: WriterArrow w a b c -> WriterArrow w a b c' -> WriterArrow w a b (c, c') #
(ArrowZero a, Monoid w) => ArrowZero (WriterArrow w a) Source #
Methods zeroArrow :: WriterArrow w a b c #
(ArrowPlus a, Monoid w) => ArrowPlus (WriterArrow w a) Source #
Methods (<+>) :: WriterArrow w a b c -> WriterArrow w a b c -> WriterArrow w a b c #
(ArrowChoice a, Monoid w) => ArrowChoice (WriterArrow w a) Source #
Methods left :: WriterArrow w a b c -> WriterArrow w a (Either b d) (Either c d) # right :: WriterArrow w a b c -> WriterArrow w a (Either d b) (Either d c) # (+++) :: WriterArrow w a b c -> WriterArrow w a b' c' -> WriterArrow w a (Either b b') (Either c c') # (\|\|\|) :: WriterArrow w a b d -> WriterArrow w a c d -> WriterArrow w a (Either b c) d #
(ArrowApply a, Monoid w) => ArrowApply (WriterArrow w a) Source #
Methods app :: WriterArrow w a (WriterArrow w a b c, b) c #
(ArrowLoop a, Monoid w) => ArrowLoop (WriterArrow w a) Source #
Methods loop :: WriterArrow w a (b, d) (c, d) -> WriterArrow w a b c #
(ArrowCircuit a, Monoid w) => ArrowCircuit (WriterArrow w a) Source #
Methods delay :: b -> WriterArrow w a b b Source #
(Arrow a, Monoid w) => Functor (WriterArrow w a b) Source #
Methods fmap :: (a -> b) -> WriterArrow w a b a -> WriterArrow w a b b # (<$) :: a -> WriterArrow w a b b -> WriterArrow w a b a #
(Arrow a, Monoid w) => Applicative (WriterArrow w a b) Source #
Methods pure :: a -> WriterArrow w a b a # (<>) :: WriterArrow w a b (a -> b) -> WriterArrow w a b a -> WriterArrow w a b b # liftA2 :: (a -> b -> c) -> WriterArrow w a b a -> WriterArrow w a b b -> WriterArrow w a b c # (>) :: WriterArrow w a b a -> WriterArrow w a b b -> WriterArrow w a b b # (<*) :: WriterArrow w a b a -> WriterArrow w a b b -> WriterArrow w a b a #
(ArrowPlus a, Monoid w) => Alternative (WriterArrow w a b) Source #
Methods empty :: WriterArrow w a b a # (<\|>) :: WriterArrow w a b a -> WriterArrow w a b a -> WriterArrow w a b a # some :: WriterArrow w a b a -> WriterArrow w a b [a] # many :: WriterArrow w a b a -> WriterArrow w a b [a] #
(ArrowPlus a, Monoid w) => Semigroup (WriterArrow w a b c) Source #
Methods (<>) :: WriterArrow w a b c -> WriterArrow w a b c -> WriterArrow w a b c # sconcat :: NonEmpty (WriterArrow w a b c) -> WriterArrow w a b c # stimes :: Integral b => b -> WriterArrow w a b c -> WriterArrow w a b c #
(ArrowPlus a, Monoid w) => Monoid (WriterArrow w a b c) Source #
Methods mempty :: WriterArrow w a b c # mappend :: WriterArrow w a b c -> WriterArrow w a b c -> WriterArrow w a b c # mconcat :: [WriterArrow w a b c] -> WriterArrow w a b c #

runWriter :: (Arrow a, Monoid w) => WriterArrow w a e b -> a e (b, w) Source #

Encapsulation of a writer computation, providing the accumulated output.

Typical usage in arrow notation:

   proc p -> do
       ...
       (result, output) <- (|runWriter cmd|)

class (ArrowWriter w a, Arrow a') => ArrowAddWriter w a a' | a -> a' where Source #

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

   instance Arrow a => ArrowAddWriter w (ArrowWriter w a) a

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

   instance ArrowAddWriter w a a' =>
       ArrowAddWriter w (FooArrow a) (FooArrow a')

Minimal complete definition

liftWriter, elimWriter

Methods

liftWriter :: a' e b -> a e b Source #

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

Typical usage in arrow notation:

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

elimWriter :: a e b -> a' e (b, w) Source #

Elimination of an output writer from a computation, providing the accumulated output.

Typical usage in arrow notation:

   proc p -> do
       ...
       (result, output) <- (|elimWriter cmd|)

Instances

ArrowAddWriter w a a' => ArrowAddWriter w (Automaton a) (Automaton a') Source #
Methods liftWriter :: Automaton a' e b -> Automaton a e b Source # elimWriter :: Automaton a e b -> Automaton a' e (b, w) Source #
(Arrow a, Monoid w) => ArrowAddWriter w (WriterArrow w a) a Source #
Methods liftWriter :: a e b -> WriterArrow w a e b Source # elimWriter :: WriterArrow w a e b -> a e (b, w) Source #
(ArrowAddWriter w a a', ArrowChoice a, ArrowChoice a') => ArrowAddWriter w (ErrorArrow ex a) (ErrorArrow ex a') Source #
Methods liftWriter :: ErrorArrow ex a' e b -> ErrorArrow ex a e b Source # elimWriter :: ErrorArrow ex a e b -> ErrorArrow ex a' e (b, w) Source #
ArrowAddWriter s a a' => ArrowAddWriter s (ReaderArrow r a) (ReaderArrow r a') Source #
Methods liftWriter :: ReaderArrow r a' e b -> ReaderArrow r a e b Source # elimWriter :: ReaderArrow r a e b -> ReaderArrow r a' e (b, s) Source #
ArrowAddWriter w a a' => ArrowAddWriter w (StateArrow s a) (StateArrow s a') Source #
Methods liftWriter :: StateArrow s a' e b -> StateArrow s a e b Source # elimWriter :: StateArrow s a e b -> StateArrow s a' e (b, w) Source #
(ArrowAddWriter w a a', Applicative f) => ArrowAddWriter w (StaticArrow f a) (StaticArrow f a') Source #
Methods liftWriter :: StaticArrow f a' e b -> StaticArrow f a e b Source # elimWriter :: StaticArrow f a e b -> StaticArrow f a' e (b, w) Source #