Safe Haskell	None
Language	Haskell2010

Polysemy.Writer

Contents

Synopsis

data Writer o m a where
- Tell :: o -> Writer o m ()
- Listen :: forall o m a. m a -> Writer o m (o, a)
- Censor :: (o -> o) -> m a -> Writer o m a
tell :: forall o. forall r. Member (Writer o) r => o -> Semantic r ()
listen :: forall o a. forall r. Member (Writer o) r => Semantic r a -> Semantic r (o, a)
censor :: forall o a. forall r. Member (Writer o) r => (o -> o) -> Semantic r a -> Semantic r a
runOutputAsWriter :: Semantic (Output o ': r) a -> Semantic (Writer o ': r) a
runWriter :: (Monoid o, Typeable o) => Semantic (Writer o ': r) a -> Semantic r (o, a)

Effect

data Writer o m a where Source #

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)
Censor :: (o -> o) -> m a -> Writer o m a

Instances

type DefiningModule Writer Source #
Instance details Defined in Polysemy.Writer type DefiningModule Writer = "Polysemy.Writer"

Actions

tell :: forall o. forall r. Member (Writer o) r => o -> Semantic r () Source #

listen :: forall o a. forall r. Member (Writer o) r => Semantic r a -> Semantic r (o, a) Source #

censor :: forall o a. forall r. Member (Writer o) r => (o -> o) -> Semantic r a -> Semantic r a Source #

Transform an Output effect into a Writer effect.

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