Data.Effect.Reader

Effects that can be used to hold environmental values in the context. Environmental values are immutable and do not change across procedures, but you can modify the value within a local scope using the local operation.

Documentation

data Ask r a where

An effect that holds a value of type r in the context (environment).

Constructors

Ask :: forall r. Ask r r

Obtain a value from the environment.

data Local r (f :: Type -> Type) a where

An effect that locally modifies the value held in the environment.

Constructors

Local

Locally modifies the value held in the environment.

Fields

• :: forall r (f :: Type -> Type) a. (r -> r)

  A function that transforms the original value to the modified value.

• -> f a

  The local scope where the modification is applied.

• -> Local r f a

Instances

() => HFunctor (Local r)

Defined in Data.Effect.Reader

Methods

hfmap :: forall (f :: Type -> Type) (g :: Type -> Type). (f :-> g) -> Local r f :-> Local r g

type LAsk r = LiftFOE (Ask r)

pattern LAsk :: forall a r f. () => (a ~ r, ()) => LiftFOE (Ask r) f a

ask :: SendFOE (Ask r) f => f r

Obtain a value from the environment.

ask' :: forall {k} (tag :: k) r f. SendFOE (Tag (Ask r) tag) f => f r

Obtain a value from the environment.

ask'' :: forall {k} (key :: k) r f. SendFOEBy key (Ask r) f => f r

Obtain a value from the environment.

local

Arguments

:: forall r a f. SendHOE (Local r) f

=> (r -> r)

-> f a

The local scope where the modification is applied.

-> f a

Locally modifies the value held in the environment.

local'

Arguments

:: forall {k} (tag :: k) r a f. SendHOE (TagH (Local r) tag) f

=> (r -> r)

-> f a

The local scope where the modification is applied.

-> f a

Locally modifies the value held in the environment.

local''

Arguments

:: forall {k} (key :: k) r a f. SendHOEBy key (Local r) f

=> (r -> r)

-> f a

The local scope where the modification is applied.

-> f a

Locally modifies the value held in the environment.

asks :: (Ask r <: f, Functor f) => (r -> a) -> f a

Obtains a value from the environment and returns it transformed by the given function.