Safe Haskell	None
Language	Haskell2010

Effectful.Reader.Dynamic

Contents

Effect
- Handlers
- Operations

Description

The dynamically dispatched variant of the Reader effect.

Note: unless you plan to change interpretations at runtime or you need the MonadReader instance for compatibility with existing code, it's recommended to use the statically dispatched variant, i.e. Effectful.Reader.Static.

Synopsis

data Reader r (a :: Type -> Type) b where
- Ask :: forall r (a :: Type -> Type). Reader r a r
- Local :: forall r (a :: Type -> Type) b. (r -> r) -> a b -> Reader r a b
runReader :: forall r (es :: [(Type -> Type) -> Type -> Type]) a. HasCallStack => r -> Eff (Reader r ': es) a -> Eff es a
withReader :: forall r1 r2 (es :: [(Type -> Type) -> Type -> Type]) a. HasCallStack => (r1 -> r2) -> Eff (Reader r2 ': es) a -> Eff (Reader r1 ': es) a
ask :: forall r (es :: [Effect]). (HasCallStack, Reader r :> es) => Eff es r
asks :: forall r (es :: [Effect]) a. (HasCallStack, Reader r :> es) => (r -> a) -> Eff es a
local :: forall r (es :: [Effect]) a. (HasCallStack, Reader r :> es) => (r -> r) -> Eff es a -> Eff es a

Effect

data Reader r (a :: Type -> Type) b where Source #

Constructors

Ask :: forall r (a :: Type -> Type). Reader r a r
Local :: forall r (a :: Type -> Type) b. (r -> r) -> a b -> Reader r a b

Instances

Instances details

type DispatchOf (Reader r) Source #
Instance details Defined in Effectful.Internal.MTL type DispatchOf (Reader r) = 'Dynamic

Handlers

runReader Source #

Arguments

:: forall r (es :: [(Type -> Type) -> Type -> Type]) a. HasCallStack
=> r	The initial environment.
-> Eff (Reader r ': es) a
-> Eff es a

Run the Reader effect with the given initial environment.

withReader Source #

Arguments

:: forall r1 r2 (es :: [(Type -> Type) -> Type -> Type]) a. HasCallStack
=> (r1 -> r2)	The function to modify the environment.
-> Eff (Reader r2 ': es) a	Computation to run in the modified environment.
-> Eff (Reader r1 ': es) a

Deprecated: withReader doesn't work correctly for all potential interpreters

Execute a computation in a modified environment.

Since: 1.1.0.0

Operations

ask :: forall r (es :: [Effect]). (HasCallStack, Reader r :> es) => Eff es r Source #

Fetch the value of the environment.

asks Source #

Arguments

:: forall r (es :: [Effect]) a. (HasCallStack, 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 Source #

Arguments

:: forall r (es :: [Effect]) a. (HasCallStack, 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