Polysemy.Internal.Union

Documentation

data Union (r :: [(* -> *) -> * -> *]) (m :: * -> *) 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

Fields

• :: SNat n

  A proof that the effect is actually in r.

• -> Yo (IndexOf r n) m a

  The effect to wrap. The functions prj and decomp can help retrieve this value later.

• -> Union r m a

Instances

Effect (Union r)

Defined in Polysemy.Internal.Union

Methods

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

weave :: (Functor s, Functor m, Functor n) => s () -> (forall x. s (m x) -> n (s 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

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 Yo e m a where

Constructors

Yo :: Functor f => e m a -> f () -> (forall x. f (m x) -> n (f x)) -> (f a -> b) -> Yo e n b

Instances

Effect (Yo e)

Defined in Polysemy.Internal.Union

Methods

fmap' :: (a -> b) -> Yo e m a -> Yo e m b

weave :: (Functor s, Functor m, Functor n) => s () -> (forall x. s (m x) -> n (s x)) -> Yo e m a -> Yo e n (s a)

hoist :: (Functor m, Functor n) => (forall x. m x -> n x) -> Yo e m a -> Yo e n a

Functor (Yo e m)

Defined in Polysemy.Internal.Union

Methods

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

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

liftYo :: Functor m => e m a -> Yo e m a

type Member e r = Member' e r

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

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 :: 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) (Yo 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 (Yo e m a)

Attempt to take an e effect out of a Union.

extract :: Union '[e] m a -> Yo 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) (Yo e m a)

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

Witnesses

data SNat :: Nat -> * 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)