Control.Effect.Writer

Documentation

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

Constructors

Tell w k

Instances

Effect (Writer w)

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))

HFunctor (Writer w)

Defined in Control.Effect.Writer

Methods

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

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

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

Defined in Control.Effect.Writer

Methods

ret :: a -> WriterC w m a

eff :: (Writer w :+: sig) (WriterC w m) (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

runWriter :: (Carrier sig m, Effect sig, Functor m, Monoid w) => Eff (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 :: (Carrier sig m, Effect sig, Functor m, Monoid w) => Eff (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

Constructors

WriterC

Fields

• runWriterC :: m (w, a)

Instances

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

Defined in Control.Effect.Writer

Methods

ret :: a -> WriterC w m a

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