polysemy-0.5.0.0: Higher-order, low-boilerplate, zero-cost free monads.

Polysemy.Internal.Union

Synopsis

# Documentation

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

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 -> Yo (IndexOf r n) m a -> Union r m a
Instances
 Functor (Union r m) Source # Instance detailsDefined in Polysemy.Internal.Union Methodsfmap :: (a -> b) -> Union r m a -> Union r m b #(<$) :: a -> Union r m b -> Union r m a # data Yo e m a where Source # Constructors  Yo :: Functor f => e m a -> f () -> (forall x. f (m x) -> n (f x)) -> (f a -> b) -> (forall x. f x -> Maybe x) -> Yo e n b Instances  Functor (Yo e m) Source # Instance detailsDefined in Polysemy.Internal.Union Methodsfmap :: (a -> b) -> Yo e m a -> Yo e m b #(<$) :: a -> Yo e m b -> Yo e m a #

type Member e r = Member' e r Source #

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

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) Source #

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

# Building Unions

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

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 Source #

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) Source #

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) Source #

Attempt to take an e effect out of a Union.

extract :: Union '[e] m a -> Yo e m a Source #

Retrieve the last effect in a Union.

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

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) Source #

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

# Witnesses

data SNat :: Nat -> Type where Source #

A singleton for Nat.

Constructors

 SZ :: SNat Z SS :: SNat n -> SNat (S n)
Instances
 Source # Instance detailsDefined in Polysemy.Internal.Union MethodstestEquality :: SNat a -> SNat b -> Maybe (a :~: b) #

data Nat Source #

The kind of type-level natural numbers.

Constructors

 Z S Nat
Instances
 Source # Instance detailsDefined in Polysemy.Internal.Union MethodstestEquality :: SNat a -> SNat b -> Maybe (a :~: b) #

class MemberNoError end r => LastMember end r | r -> end where Source #

A proof that end is the last effect in the row.

Since: 0.5.0.0

Methods

decompLast :: Union r m a -> Either (Union r m a) (Union '[end] m a) Source #

Instances
 LastMember end (end ': ([] :: [Effect])) Source # Instance detailsDefined in Polysemy.Internal.Union MethodsdecompLast :: Union (end ': []) m a -> Either (Union (end ': []) m a) (Union (end ': []) m a) Source # (LastMember end r, MemberNoError end (eff ': r)) => LastMember end (eff ': r) Source # Instance detailsDefined in Polysemy.Internal.Union MethodsdecompLast :: Union (eff ': r) m a -> Either (Union (eff ': r) m a) (Union (end ': []) m a) Source #