servant-0.19.1: A family of combinators for defining webservices APIs

Safe Haskell | Safe-Inferred
Language | Haskell2010

Servant.API.UVerb.Union

Description

Type-level code for implementing and using `UVerb`. Heavily inspired by world-peace.

Synopsis

- type IsMember (a :: u) (as :: [u]) = (Unique as, CheckElemIsMember a as, UElem a as)
- type family Unique xs :: Constraint where ...
- type Union = NS I
- inject :: UElem x xs => f x -> NS f xs
- eject :: UElem x xs => NS f xs -> Maybe (f x)
- foldMapUnion :: forall (c :: * -> Constraint) (a :: *) (as :: [*]). All c as => Proxy c -> (forall x. c x => x -> a) -> Union as -> a
- matchUnion :: forall (a :: *) (as :: [*]). IsMember a as => Union as -> Maybe a

# Documentation

type IsMember (a :: u) (as :: [u]) = (Unique as, CheckElemIsMember a as, UElem a as) Source #

type family Unique xs :: Constraint where ... Source #

Equations

Unique xs = If (Nubbed xs == 'True) (() :: Constraint) (TypeError (DuplicateElementError xs)) |

type Union = NS I Source #

inject :: UElem x xs => f x -> NS f xs Source #

eject :: UElem x xs => NS f xs -> Maybe (f x) Source #

foldMapUnion :: forall (c :: * -> Constraint) (a :: *) (as :: [*]). All c as => Proxy c -> (forall x. c x => x -> a) -> Union as -> a Source #

Convenience function to apply a function to an unknown union element using a type class. All elements of the union must have instances in the type class, and the function is applied unconditionally.

See also: `matchUnion`.

matchUnion :: forall (a :: *) (as :: [*]). IsMember a as => Union as -> Maybe a Source #

Convenience function to extract a union element using `cast`, ie. return the value if the selected type happens to be the actual type of the union in this value, or `Nothing` otherwise.

See also: `foldMapUnion`.