Safe Haskell	None
Language	Haskell2010

Control.Effect.Writer

Synopsis

data Writer w (m :: * -> *) k = Tell w k
tell :: (Member (Writer w) sig, Carrier sig m) => w -> m ()
runWriter :: (Carrier sig m, Effect sig, Functor m, Monoid w) => Eff (WriterC w m) a -> m (w, a)
execWriter :: (Carrier sig m, Effect sig, Functor m, Monoid w) => Eff (WriterC w m) a -> m w
newtype WriterC w m a = WriterC {
- runWriterC :: m (w, a)
}

Documentation

data Writer w (m :: * -> *) k Source #

Constructors

Instances

Effect (Writer w) Source #
Instance details Defined in Control.Effect.Writer Methods handle :: Functor f => f () -> (forall x. f (m x) -> n (f x)) -> Writer w m (m a) -> Writer w n (n (f a)) Source #
HFunctor (Writer w) Source #
Instance details Defined in Control.Effect.Writer Methods fmap' :: (a -> b) -> Writer w m a -> Writer w m b Source # hmap :: (forall x. m x -> n x) -> Writer w m a -> Writer w n a Source #
Functor (Writer w m) Source #
Instance details 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, Functor m) => Carrier (Writer w :+: sig) (WriterC w m) Source #
Instance details Defined in Control.Effect.Writer Methods ret :: a -> WriterC w m a Source # eff :: (Writer w :+: sig) (WriterC w m) (WriterC w m a) -> WriterC w m a Source #

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

Write a value to the log.

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

runWriter :: (Carrier sig m, Effect sig, Functor m, Monoid w) => Eff (WriterC w m) a -> m (w, a) Source #

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)

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 Source #

Constructors

WriterC
Fields runWriterC :: m (w, a)

Instances

(Monoid w, Carrier sig m, Effect sig, Functor m) => Carrier (Writer w :+: sig) (WriterC w m) Source #
Instance details Defined in Control.Effect.Writer Methods ret :: a -> WriterC w m a Source # eff :: (Writer w :+: sig) (WriterC w m) (WriterC w m a) -> WriterC w m a Source #