Moduleeffectful-core-2.7.1.2GHC2021

Effectful.Labeled.Reader

Convenience functions for the Labeled Reader effect.

Effect

1 declaration

datadata Reader r (a :: Type -> Type) b where

Instances1DispatchOf

type DispatchOf (Reader r) = 'DynamicDefined in effectful-core-2.7.1.2 · Effectful.Internal.Effect.Dynamic

valuerunReader

Run the Reader effect with the given initial environment (via Effectful.Reader.Static).

valueask :: (HasCallStack, Labeled label (Reader r) :> es) => Eff es r

Fetch the value of the environment.

valueasks

Retrieve a function of the current environment.

asks f ≡ f <$> ask

valuelocal

Execute a computation in a modified environment.

runReader r (local f m) ≡ runReader (f r) m

1 declaration

newtypenewtype Labeled (label :: k) (e :: Effect) (a :: Type -> Type) b where

Assign a label to an effect.

Note: labeled effects are best used together with the effectful-plugin package, as it significantly improves their usability.

The constructor is for sending labeled operations of a dynamically dispatched effect to the handler:

Example1 expression

>>> import Effectful.Dispatch.Dynamic

Example1 expression

>>> :{  data X :: Effect where    X :: X m Int  type instance DispatchOf X = Dynamic:}

Example1 expression

>>> :{  runPureEff . runLabeled @"x" (interpret_ $ \X -> pure 333) $ do    send $ Labeled @"x" X:}333

Instances2DispatchOf, StaticRep

type DispatchOf (Labeled label e) = DispatchOf eDefined in effectful-core-2.7.1.2 · Effectful.Labeled
data StaticRep (Labeled label e)Defined in effectful-core-2.7.1.2 · Effectful.Labeled