Polysemy.Internal.Union

Documentation

data Union (r :: EffectRow) (m :: Type -> Type) a where

An extensible, type-safe union. The r type parameter is a type-level list of effects, any one of which may be held within the Union.

Constructors

Union :: SNat n -> Weaving (IndexOf r n) m a -> Union r m a

Instances

Functor (Union r m)

Defined in Polysemy.Internal.Union

Methods

fmap :: (a -> b) -> Union r m a -> Union r m b

(<$) :: a -> Union r m b -> Union r m a

data Weaving e m a where

Constructors

Weaving

Fields

• :: Functor f
• => { weaveEffect :: e m a

  The original effect GADT originally lifted via send. There is an invariant that m ~ Sem r0, where r0 is the effect row that was in scope when this Weaving was originally created.

•    , weaveState :: f ()

  A piece of state that other effects' interpreters have already woven through this Weaving. f is a Functor, so you can always fmap into this thing.

•    , weaveDistrib :: forall x. f (m x) -> n (f x)

  Distribute f by transforming m into n. We have invariants on m and n, which means in actuality this function looks like f (Sem (Some ': Effects ': r) x) -> Sem r (f x).

•    , weaveResult :: f a -> b

  Even though f a is the moral resulting type of Weaving, we can't expose that fact; such a thing would prevent Sem from being a Monad.

•    , weaveInspect :: forall x. f x -> Maybe x

  A function for attempting to see inside an f. This is no guarantees that such a thing will succeed (for example, Error might have thrown.)

•    } -> Weaving e n b

Instances

Functor (Weaving e m)

Defined in Polysemy.Internal.Union

Methods

fmap :: (a -> b) -> Weaving e m a -> Weaving e m b

(<$) :: a -> Weaving e m b -> Weaving e m a

type Member e r = MemberNoError e r

A proof that the effect e is available somewhere inside of the effect stack r.

type MemberWithError e r = (MemberNoError e r, WhenStuck (IndexOf r (Found r e)) (AmbiguousSend r e))

weave :: (Functor s, Functor m, Functor n) => s () -> (forall x. s (m x) -> n (s x)) -> (forall x. s x -> Maybe x) -> Union r m a -> Union r n (s a)

hoist :: (Functor m, Functor n) => (forall x. m x -> n x) -> Union r m a -> Union r n a

Building Unions

inj :: forall r e a m. (Functor m, Member e r) => e m a -> Union r m a

Lift an effect e into a Union capable of holding it.

weaken :: forall e r m a. Union r m a -> Union (e ': r) m a

Weaken a Union so it is capable of storing a new sort of effect.

Using Unions

decomp :: Union (e ': r) m a -> Either (Union r m a) (Weaving e m a)

Decompose a Union. Either this union contains an effect e---the head of the r list---or it doesn't.

prj :: forall e r a m. Member e r => Union r m a -> Maybe (Weaving e m a)

Attempt to take an e effect out of a Union.

extract :: Union '[e] m a -> Weaving e m a

Retrieve the last effect in a Union.

absurdU :: Union '[] m a -> b

An empty union contains nothing, so this function is uncallable.

decompCoerce :: Union (e ': r) m a -> Either (Union (f ': r) m a) (Weaving e m a)

Like decomp, but allows for a more efficient reinterpret function.

Witnesses

data SNat :: Nat -> Type where

A singleton for Nat.

Constructors

SZ :: SNat Z

SS :: SNat n -> SNat (S n)

Instances

TestEquality SNat

Defined in Polysemy.Internal.Union

Methods

testEquality :: SNat a -> SNat b -> Maybe (a :~: b)

data Nat

The kind of type-level natural numbers.

Constructors

Z

S Nat

Instances

TestEquality SNat

Defined in Polysemy.Internal.Union

Methods

testEquality :: SNat a -> SNat b -> Maybe (a :~: b)