Control.Effect.Writer

Writer effect

data Writer w m k

Constructors

Tell w (m k)

Listen (m a) (w -> a -> m k)

Censor (w -> w) (m a) (a -> m k)

Instances

Effect (Writer w)

Defined in Control.Effect.Writer

Methods

handle :: (Functor f, Monad m) => f () -> (forall x. f (m x) -> n (f x)) -> Writer w m a -> Writer w n (f a)

HFunctor (Writer w)

Defined in Control.Effect.Writer

Methods

fmap' :: Functor (Writer w f) => (a -> b) -> Writer w f a -> Writer w f b

hmap :: Functor m => (forall x. m x -> n x) -> Writer w m a -> Writer w n a

Functor m => Functor (Writer w m)

Defined in Control.Effect.Writer

Methods

fmap :: (a -> b) -> Writer w m a -> Writer w m b

(<$) :: a -> Writer w m b -> Writer w m a

(Monoid w, Carrier sig m, Effect sig) => Carrier (Writer w :+: sig) (WriterC w m)

Defined in Control.Effect.Writer

Methods

eff :: (Writer w :+: sig) (WriterC w m) a -> WriterC w m a

tell :: (Member (Writer w) sig, Carrier sig m) => w -> m ()

Write a value to the log.

fst (run (runWriter (mapM_ (tell . Sum) (0 : ws)))) === foldMap Sum ws

listen :: (Member (Writer w) sig, Carrier sig m) => m a -> m (w, a)

Run a computation, returning the pair of its output and its result.

run (runWriter (fst <$ tell (Sum a) <*> listen @(Sum Integer) (tell (Sum b)))) === (Sum a <> Sum b, Sum b)

listens :: (Member (Writer w) sig, Carrier sig m) => (w -> b) -> m a -> m (b, a)

Run a computation, applying a function to its output and returning the pair of the modified output and its result.

run (runWriter (fst <$ tell (Sum a) <*> listens @(Sum Integer) (applyFun f) (tell (Sum b)))) === (Sum a <> Sum b, applyFun f (Sum b))

censor :: (Member (Writer w) sig, Carrier sig m) => (w -> w) -> m a -> m a

Run a computation, modifying its output with the passed function.

run (execWriter (censor (applyFun f) (tell (Sum a)))) === applyFun f (Sum a)

run (execWriter (tell (Sum a) *> censor (applyFun f) (tell (Sum b)) *> tell (Sum c))) === (Sum a <> applyFun f (Sum b) <> Sum c)

Writer carrier

runWriter :: Monoid w => WriterC w m a -> m (w, a)

Run a Writer effect with a Monoidal log, producing the final log alongside the result value.

run (runWriter (tell (Sum a) *> pure b)) === (Sum a, b)

execWriter :: (Monoid w, Functor m) => WriterC w m a -> m w

Run a Writer effect with a Monoidal log, producing the final log and discarding the result value.

run (execWriter (tell (Sum a) *> pure b)) === Sum a

newtype WriterC w m a

A space-efficient carrier for Writer effects.

This is based on a post Gabriel Gonzalez made to the Haskell mailing list: https://mail.haskell.org/pipermail/libraries/2013-March/019528.html

Constructors

WriterC

Fields

• runWriterC :: StateC w m a

Instances

MonadTrans (WriterC w)

Defined in Control.Effect.Writer

Methods

lift :: Monad m => m a -> WriterC w m a

Monad m => Monad (WriterC w m)

Defined in Control.Effect.Writer

Methods

(>>=) :: WriterC w m a -> (a -> WriterC w m b) -> WriterC w m b

(>>) :: WriterC w m a -> WriterC w m b -> WriterC w m b

return :: a -> WriterC w m a

fail :: String -> WriterC w m a

Functor m => Functor (WriterC w m)

Defined in Control.Effect.Writer

Methods

fmap :: (a -> b) -> WriterC w m a -> WriterC w m b

(<$) :: a -> WriterC w m b -> WriterC w m a

MonadFix m => MonadFix (WriterC w m)

Defined in Control.Effect.Writer

Methods

mfix :: (a -> WriterC w m a) -> WriterC w m a

MonadFail m => MonadFail (WriterC w m)

Defined in Control.Effect.Writer

Methods

fail :: String -> WriterC w m a

Monad m => Applicative (WriterC w m)

Defined in Control.Effect.Writer

Methods

pure :: a -> WriterC w m a

(<*>) :: WriterC w m (a -> b) -> WriterC w m a -> WriterC w m b

liftA2 :: (a -> b -> c) -> WriterC w m a -> WriterC w m b -> WriterC w m c

(*>) :: WriterC w m a -> WriterC w m b -> WriterC w m b

(<*) :: WriterC w m a -> WriterC w m b -> WriterC w m a

MonadIO m => MonadIO (WriterC w m)

Defined in Control.Effect.Writer

Methods

liftIO :: IO a -> WriterC w m a

(Alternative m, Monad m) => Alternative (WriterC w m)

Defined in Control.Effect.Writer

Methods

empty :: WriterC w m a

(<|>) :: WriterC w m a -> WriterC w m a -> WriterC w m a

some :: WriterC w m a -> WriterC w m [a]

many :: WriterC w m a -> WriterC w m [a]

(Alternative m, Monad m) => MonadPlus (WriterC w m)

Defined in Control.Effect.Writer

Methods

mzero :: WriterC w m a

mplus :: WriterC w m a -> WriterC w m a -> WriterC w m a

(Monoid w, Carrier sig m, Effect sig) => Carrier (Writer w :+: sig) (WriterC w m)

Defined in Control.Effect.Writer

Methods

eff :: (Writer w :+: sig) (WriterC w m) a -> WriterC w m a

Re-exports

class (HFunctor sig, Monad m) => Carrier sig m | m -> sig

The class of carriers (results) for algebras (effect handlers) over signatures (effects), whose actions are given by the eff method.

Minimal complete definition

eff

Instances

Carrier Pure PureC

Defined in Control.Effect.Carrier

Methods

eff :: Pure PureC a -> PureC a

(HFunctor eff, Carrier sig m, Member eff sig) => Carrier sig (InterposeC eff m)

Defined in Control.Effect.Interpose

Methods

eff :: sig (InterposeC eff m) a -> InterposeC eff m a

Monad m => Carrier (Lift m) (LiftC m)

Defined in Control.Effect.Lift

Methods

eff :: Lift m (LiftC m) a -> LiftC m a

(Carrier sig m, MonadIO m) => Carrier (Resource :+: sig) (ResourceC m)

Defined in Control.Effect.Resource

Methods

eff :: (Resource :+: sig) (ResourceC m) a -> ResourceC m a

(Carrier sig m, Effect sig) => Carrier (NonDet :+: sig) (NonDetC m)

Defined in Control.Effect.NonDet

Methods

eff :: (NonDet :+: sig) (NonDetC m) a -> NonDetC m a

(Carrier sig m, Effect sig) => Carrier (NonDet :+: sig) (OnceC m)

Defined in Control.Effect.Cull

Methods

eff :: (NonDet :+: sig) (OnceC m) a -> OnceC m a

(Carrier sig m, Effect sig) => Carrier (Fresh :+: sig) (FreshC m)

Defined in Control.Effect.Fresh

Methods

eff :: (Fresh :+: sig) (FreshC m) a -> FreshC m a

(Carrier sig m, Effect sig) => Carrier (Fail :+: sig) (FailC m)

Defined in Control.Effect.Fail

Methods

eff :: (Fail :+: sig) (FailC m) a -> FailC m a

(Carrier sig m, Effect sig) => Carrier (Cut :+: (NonDet :+: sig)) (CutC m)

Defined in Control.Effect.Cut

Methods

eff :: (Cut :+: (NonDet :+: sig)) (CutC m) a -> CutC m a

(Carrier sig m, Effect sig) => Carrier (Cull :+: (NonDet :+: sig)) (CullC m)

Defined in Control.Effect.Cull

Methods

eff :: (Cull :+: (NonDet :+: sig)) (CullC m) a -> CullC m a

(Carrier sig m, Effect sig) => Carrier (Trace :+: sig) (TraceByReturningC m)

Defined in Control.Effect.Trace

Methods

eff :: (Trace :+: sig) (TraceByReturningC m) a -> TraceByReturningC m a

Carrier sig m => Carrier (Trace :+: sig) (TraceByIgnoringC m)

Defined in Control.Effect.Trace

Methods

eff :: (Trace :+: sig) (TraceByIgnoringC m) a -> TraceByIgnoringC m a

(MonadIO m, Carrier sig m) => Carrier (Trace :+: sig) (TraceByPrintingC m)

Defined in Control.Effect.Trace

Methods

eff :: (Trace :+: sig) (TraceByPrintingC m) a -> TraceByPrintingC m a

(HFunctor eff, Carrier sig m) => Carrier (eff :+: sig) (InterpretC eff m)

Defined in Control.Effect.Interpret

Methods

eff :: (eff :+: sig) (InterpretC eff m) a -> InterpretC eff m a

(Carrier sig m, Effect sig) => Carrier (State s :+: sig) (StateC s m)

Defined in Control.Effect.State.Strict

Methods

eff :: (State s :+: sig) (StateC s m) a -> StateC s m a

(Carrier sig m, Effect sig) => Carrier (State s :+: sig) (StateC s m)

Defined in Control.Effect.State.Lazy

Methods

eff :: (State s :+: sig) (StateC s m) a -> StateC s m a

Carrier sig m => Carrier (Reader r :+: sig) (ReaderC r m)

Defined in Control.Effect.Reader

Methods

eff :: (Reader r :+: sig) (ReaderC r m) a -> ReaderC r m a

(Carrier sig m, Effect sig, RandomGen g) => Carrier (Random :+: sig) (RandomC g m)

Defined in Control.Effect.Random

Methods

eff :: (Random :+: sig) (RandomC g m) a -> RandomC g m a

(Carrier sig m, Effect sig) => Carrier (Error e :+: sig) (ErrorC e m)

Defined in Control.Effect.Error

Methods

eff :: (Error e :+: sig) (ErrorC e m) a -> ErrorC e m a

Carrier sig m => Carrier (Resumable err :+: sig) (ResumableWithC err m)

Defined in Control.Effect.Resumable

Methods

eff :: (Resumable err :+: sig) (ResumableWithC err m) a -> ResumableWithC err m a

(Carrier sig m, Effect sig) => Carrier (Resumable err :+: sig) (ResumableC err m)

Defined in Control.Effect.Resumable

Methods

eff :: (Resumable err :+: sig) (ResumableC err m) a -> ResumableC err m a

(Monoid w, Carrier sig m, Effect sig) => Carrier (Writer w :+: sig) (WriterC w m)

Defined in Control.Effect.Writer

Methods

eff :: (Writer w :+: sig) (WriterC w m) a -> WriterC w m a

(HFunctor eff, Carrier sig m, Effect sig) => Carrier (eff :+: sig) (InterpretStateC eff s m)

Defined in Control.Effect.Interpret

Methods

eff :: (eff :+: sig) (InterpretStateC eff s m) a -> InterpretStateC eff s m a

class Member (sub :: (* -> *) -> * -> *) sup

Minimal complete definition

inj, prj

Instances

Member sub sub

Defined in Control.Effect.Sum

Methods

inj :: sub m a -> sub m a

prj :: sub m a -> Maybe (sub m a)

Member sub sup => Member sub (sub' :+: sup)

Defined in Control.Effect.Sum

Methods

inj :: sub m a -> (sub' :+: sup) m a

prj :: (sub' :+: sup) m a -> Maybe (sub m a)

Member sub (sub :+: sup)

Defined in Control.Effect.Sum

Methods

inj :: sub m a -> (sub :+: sup) m a

prj :: (sub :+: sup) m a -> Maybe (sub m a)

run :: PureC a -> a

Run an action exhausted of effects to produce its final result value.