Effectful.Labeled.Reader

Convenience functions for the Labeled Reader effect.

Since: 2.4.0.0

Effect

data Reader r :: Effect where

Constructors

Ask :: Reader r m r

Local :: (r -> r) -> m a -> Reader r m a

Instances

type DispatchOf (Reader r)

Defined in Effectful.Reader.Dynamic

type DispatchOf (Reader r) = 'Dynamic

Handlers

runReader

Arguments

:: forall label r es a. HasCallStack

=> r

The initial environment.

-> Eff (Labeled label (Reader r) : es) a

-> Eff es a

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

Operations

ask :: forall label r es. (HasCallStack, Labeled label (Reader r) :> es) => Eff es r

Fetch the value of the environment.

asks

Arguments

:: forall label r es a. (HasCallStack, Labeled label (Reader r) :> es)

=> (r -> a)

The function to apply to the environment.

-> Eff es a

Retrieve a function of the current environment.

asks f ≡ f <$> ask

local

Arguments

:: forall label r es a. (HasCallStack, Labeled label (Reader r) :> es)

=> (r -> r)

The function to modify the environment.

-> Eff es a

-> Eff es a

Execute a computation in a modified environment.

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