Data.Union

Extensible type-safe unions.

>>> let a = openUnion # (5 :: Int) :: OpenUnion '[Bool, Int]

>>> a ^? openUnion @Int
Just 5

>>> a ^? openUnion @Bool
Nothing

>>> a ^? openUnion @Char
<interactive>:7:6: error:
    • No instance for (UElem Char '[] (RIndex Char '[]))
        arising from a use of ‘openUnion’
    • In the second argument of ‘(^?)’, namely ‘openUnion @Char’
      In the expression: a ^? openUnion @Char
      In an equation for ‘it’: it = a ^? openUnion @Char

Documentation

data Union (f :: u -> *) (as :: [u]) where

A union is parameterized by a universe u, an interpretation f and a list of labels as. The labels of the union are given by inhabitants of the kind u; the type of values at any label a :: u is given by its interpretation f a :: *.

Constructors

This :: !(f a) -> Union f (a ': as)

That :: !(Union f as) -> Union f (a ': as)

Instances

(Eq (f a2), Eq (Union f as)) => Eq (Union f (a2 ': as))

Defined in Data.Union

Methods

(==) :: Union f (a2 ': as) -> Union f (a2 ': as) -> Bool

(/=) :: Union f (a2 ': as) -> Union f (a2 ': as) -> Bool

Eq (Union f ([] :: [u]))

Defined in Data.Union

Methods

(==) :: Union f [] -> Union f [] -> Bool

(/=) :: Union f [] -> Union f [] -> Bool

(Ord (f a2), Ord (Union f as)) => Ord (Union f (a2 ': as))

Defined in Data.Union

Methods

compare :: Union f (a2 ': as) -> Union f (a2 ': as) -> Ordering

(<) :: Union f (a2 ': as) -> Union f (a2 ': as) -> Bool

(<=) :: Union f (a2 ': as) -> Union f (a2 ': as) -> Bool

(>) :: Union f (a2 ': as) -> Union f (a2 ': as) -> Bool

(>=) :: Union f (a2 ': as) -> Union f (a2 ': as) -> Bool

max :: Union f (a2 ': as) -> Union f (a2 ': as) -> Union f (a2 ': as)

min :: Union f (a2 ': as) -> Union f (a2 ': as) -> Union f (a2 ': as)

Ord (Union f ([] :: [u]))

Defined in Data.Union

Methods

compare :: Union f [] -> Union f [] -> Ordering

(<) :: Union f [] -> Union f [] -> Bool

(<=) :: Union f [] -> Union f [] -> Bool

(>) :: Union f [] -> Union f [] -> Bool

(>=) :: Union f [] -> Union f [] -> Bool

max :: Union f [] -> Union f [] -> Union f []

min :: Union f [] -> Union f [] -> Union f []

(Show (f a2), Show (Union f as)) => Show (Union f (a2 ': as))

Defined in Data.Union

Methods

showsPrec :: Int -> Union f (a2 ': as) -> ShowS

show :: Union f (a2 ': as) -> String

showList :: [Union f (a2 ': as)] -> ShowS

Show (Union f ([] :: [u]))

Defined in Data.Union

Methods

showsPrec :: Int -> Union f [] -> ShowS

show :: Union f [] -> String

showList :: [Union f []] -> ShowS

Generic (Union f (a ': as))

Defined in Data.Union

Associated Types

type Rep (Union f (a ': as)) :: * -> *

Methods

from :: Union f (a ': as) -> Rep (Union f (a ': as)) x

to :: Rep (Union f (a ': as)) x -> Union f (a ': as)

Generic (Union f ([] :: [u]))

Defined in Data.Union

Associated Types

type Rep (Union f []) :: * -> *

Methods

from :: Union f [] -> Rep (Union f []) x

to :: Rep (Union f []) x -> Union f []

(f ~ Identity, Exception a, Typeable as, Exception (Union f as)) => Exception (Union f (a ': as))

Defined in Data.Union

Methods

toException :: Union f (a ': as) -> SomeException

fromException :: SomeException -> Maybe (Union f (a ': as))

displayException :: Union f (a ': as) -> String

f ~ Identity => Exception (Union f ([] :: [*]))

Defined in Data.Union

Methods

toException :: Union f [] -> SomeException

fromException :: SomeException -> Maybe (Union f [])

displayException :: Union f [] -> String

(NFData (f a2), NFData (Union f as)) => NFData (Union f (a2 ': as))

Defined in Data.Union

Methods

rnf :: Union f (a2 ': as) -> ()

NFData (Union f ([] :: [u]))

Defined in Data.Union

Methods

rnf :: Union f [] -> ()

(Hashable (f a2), Hashable (Union f as)) => Hashable (Union f (a2 ': as))

Defined in Data.Union

Methods

hashWithSalt :: Int -> Union f (a2 ': as) -> Int

hash :: Union f (a2 ': as) -> Int

Hashable (Union f ([] :: [u]))

Defined in Data.Union

Methods

hashWithSalt :: Int -> Union f [] -> Int

hash :: Union f [] -> Int

type Rep (Union f (a ': as))

Defined in Data.Union

type Rep (Union f (a ': as)) = C1 (MetaCons "This" PrefixI False) (Rec0 (f a)) :+: C1 (MetaCons "That" PrefixI False) (Rec0 (Union f as))

type Rep (Union f ([] :: [u]))

Defined in Data.Union

type Rep (Union f ([] :: [u])) = (V1 :: * -> *)

union :: (Union f as -> c) -> (f a -> c) -> Union f (a ': as) -> c

Case analysis for unions.

absurdUnion :: Union f '[] -> a

Since a union with an empty list of labels is uninhabited, we can recover any type from it.

umap :: (forall a. f a -> g a) -> Union f as -> Union g as

_This :: Prism (Union f (a ': as)) (Union f (b ': as)) (f a) (f b)

_That :: Prism (Union f (a ': as)) (Union f (a ': bs)) (Union f as) (Union f bs)

class i ~ RIndex a as => UElem (a :: u) (as :: [u]) (i :: Nat) where

Minimal complete definition

uprism | ulift, umatch

Methods

uprism :: Prism' (Union f as) (f a)

ulift :: f a -> Union f as

umatch :: Union f as -> Maybe (f a)

Instances

UElem (a2 :: a1) (a2 ': as :: [a1]) Z

Defined in Data.Union

Methods

uprism :: (Choice p, Applicative f) => p (f a2) (f (f a2)) -> p (Union f (a2 ': as)) (f (Union f (a2 ': as)))

ulift :: f a2 -> Union f (a2 ': as)

umatch :: Union f (a2 ': as) -> Maybe (f a2)

(RIndex a2 (b ': as) ~ S i, UElem a2 as i) => UElem (a2 :: a1) (b ': as :: [a1]) (S i)

Defined in Data.Union

Methods

uprism :: (Choice p, Applicative f) => p (f a2) (f (f a2)) -> p (Union f (b ': as)) (f (Union f (b ': as)))

ulift :: f a2 -> Union f (b ': as)

umatch :: Union f (b ': as) -> Maybe (f a2)

class is ~ RImage as bs => USubset (as :: [u]) (bs :: [u]) is where

Minimal complete definition

usubset | urelax, urestrict

Methods

usubset :: Prism' (Union f bs) (Union f as)

urelax :: Union f as -> Union f bs

urestrict :: Union f bs -> Maybe (Union f as)

Instances

USubset ([] :: [u]) (bs :: [u]) ([] :: [Nat])

Defined in Data.Union

Methods

usubset :: (Choice p, Applicative f) => p (Union f []) (f (Union f [])) -> p (Union f bs) (f (Union f bs))

urelax :: Union f [] -> Union f bs

urestrict :: Union f bs -> Maybe (Union f [])

(UElem a bs i, USubset as bs is) => USubset (a ': as :: [u]) (bs :: [u]) (i ': is)

Defined in Data.Union

Methods

usubset :: (Choice p, Applicative f) => p (Union f (a ': as)) (f (Union f (a ': as))) -> p (Union f bs) (f (Union f bs))

urelax :: Union f (a ': as) -> Union f bs

urestrict :: Union f bs -> Maybe (Union f (a ': as))

type OpenUnion = Union Identity

openUnion :: forall a as. UElem a as (RIndex a as) => Prism' (OpenUnion as) a