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 :> (e ': es)

Defined in Effectful.Internal.Effect

Methods

reifyIndex :: Int

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

Defined in Effectful.Internal.Effect

Methods

reifyIndex :: Int

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

Deprecated: Usage of (:>>) slows down GHC too much. See https://github.com/haskell-effectful/effectful/issues/52#issuecomment-1269155485 for more information.

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 KnownPrefix es => Subset (subEs :: [Effect]) (es :: [Effect]) where

Provide evidence that subEs is a subset of es.

Minimal complete definition

Nothing

Methods

subsetFullyKnown :: Bool

reifyIndices :: [Int]

Instances

(KnownPrefix es, IsUnknownSuffixOf subEs es) => Subset subEs es

Defined in Effectful.Internal.Effect

Methods

subsetFullyKnown :: Bool

reifyIndices :: [Int]

KnownPrefix es => Subset ('[] :: [Effect]) es

Defined in Effectful.Internal.Effect

Methods

subsetFullyKnown :: Bool

reifyIndices :: [Int]

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

Defined in Effectful.Internal.Effect

Methods

subsetFullyKnown :: Bool

reifyIndices :: [Int]

class Subset subEs es => KnownSubset (subEs :: [Effect]) (es :: [Effect])

Provide evidence that subEs is a known subset of es.

Instances

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

Defined in Effectful.Internal.Effect

(e :> es, KnownSubset subEs es) => KnownSubset (e ': subEs) es

Defined in Effectful.Internal.Effect

class KnownPrefix (es :: [Effect]) where

Calculate length of a statically known prefix of es.

Methods

prefixLength :: Int

Instances

KnownPrefix es

Defined in Effectful.Internal.Effect

Methods

prefixLength :: Int

KnownPrefix es => KnownPrefix (e ': es)

Defined in Effectful.Internal.Effect

Methods

prefixLength :: Int

class IsUnknownSuffixOf (subEs :: [Effect]) (es :: [Effect])

Require that subEs is the unknown suffix of es.

Instances

subEs ~ es => IsUnknownSuffixOf subEs es

Defined in Effectful.Internal.Effect

IsUnknownSuffixOf subEs es => IsUnknownSuffixOf subEs (e ': es)

Defined in Effectful.Internal.Effect

type family (xs :: [Effect]) ++ (ys :: [Effect]) :: [Effect] where ... infixr 5

Append two type-level lists together.

Equations

'[] ++ ys = ys

(x : xs) ++ ys = x : (xs ++ ys)

class KnownEffects (es :: [Effect]) where

Calculate length of a list of known effects.

Minimal complete definition

Nothing

Methods

knownEffectsLength :: Int

Instances

KnownEffects ('[] :: [Effect])

Defined in Effectful.Internal.Effect

Methods

knownEffectsLength :: Int

KnownEffects es => KnownEffects (e ': es)

Defined in Effectful.Internal.Effect

Methods

knownEffectsLength :: Int

Re-exports

type Type = TYPE LiftedRep

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