Effectful.Internal.Effect

Type-safe indexing for Env.

This module is intended for internal use only, and may change without warning in subsequent releases.

Documentation

type Effect = (Type -> Type) -> Type -> Type

The kind of effects.

class (e :: Effect) :> (es :: [Effect]) where

A constraint that requires that a particular effect e is a member of the type-level list es. This is used to parameterize an Eff computation over an arbitrary list of effects, so long as e is somewhere in the list.

For example, a computation that only needs access to a mutable value of type Integer would have the following type:

State Integer :> es => Eff es ()

Minimal complete definition

Nothing

Methods

reifyIndex :: Int

Get the position of e in es.

Note: GHC is kind enough to cache these values as they're top level CAFs, so the lookup is amortized O(1) without any language level tricks.

Instances

(TypeError (('Text "There is no handler for '" :<>: 'ShowType e) :<>: 'Text "' in the context") :: Constraint) => e :> ('[] :: [Effect])

Defined in Effectful.Internal.Effect

Methods

reifyIndex :: Int

e :> es => e :> (x ': es)

Defined in Effectful.Internal.Effect

Methods

reifyIndex :: Int

e :> (e ': es)

Defined in Effectful.Internal.Effect

Methods

reifyIndex :: Int

type family xs :>> es :: Constraint where ...

Convenience operator for expressing that a function uses multiple effects in a more concise way than enumerating them all with (:>).

[E1, E2, ..., En] :>> es ≡ (E1 :> es, E2 :> es, ..., En :> es)

Equations

'[] :>> es = ()

(x ': xs) :>> es = (x :> es, xs :>> es)

class Subset (xs :: [Effect]) (es :: [Effect]) where

Provide evidence that xs is a subset of es.

Minimal complete definition

Nothing

Methods

reifyIndices :: [Int]

Instances

Subset ('[] :: [Effect]) es

Defined in Effectful.Internal.Effect

Methods

reifyIndices :: [Int]

(e :> es, Subset xs es) => Subset (e ': xs) es

Defined in Effectful.Internal.Effect

Methods

reifyIndices :: [Int]

Re-exports

type Type = Type

The kind of types with lifted values. For example Int :: Type.