Polysemy.Writer

Effect

data Writer o m a where

An effect capable of emitting and intercepting messages.

Constructors

Tell :: o -> Writer o m ()

Listen :: forall o m a. m a -> Writer o m (o, a)

Pass :: m (o -> o, a) -> Writer o m a

Instances

type DefiningModule Writer

Defined in Polysemy.Writer

type DefiningModule Writer = "Polysemy.Writer"

Actions

tell :: forall o r. MemberWithError (Writer o) r => o -> Sem r ()

listen :: forall o r a. MemberWithError (Writer o) r => Sem r a -> Sem r (o, a)

pass :: forall o r a. MemberWithError (Writer o) r => Sem r (o -> o, a) -> Sem r a

censor :: Member (Writer o) r => (o -> o) -> Sem r a -> Sem r a

Since: 0.7.0.0

Interpretations

runWriter :: Monoid o => Sem (Writer o ': r) a -> Sem r (o, a)

Run a Writer effect in the style of WriterT (but without the nasty space leak!)

Interpretations for Other Effects

outputToWriter :: Member (Writer o) r => Sem (Output o ': r) a -> Sem r a

Transform an Output effect into a Writer effect.

Since: 1.0.0.0