src/Rel8/Column/Either.hs · rel8

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rel8/src/Rel8/Column/Either.hs

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1{-# language DataKinds #-}

2{-# language StandaloneKindSignatures #-}

3{-# language TypeFamilyDependencies #-}

5module Rel8.Column.Either

6 ( HEither

7 )

8where

10-- base

11import Data.Kind ( Type )

12import Prelude

14-- rel8

15import Rel8.Aggregate ( Aggregate )

16import Rel8.Expr ( Expr )

17import qualified Rel8.Schema.Kind as K

18import Rel8.Schema.Name ( Name )

19import Rel8.Schema.Result ( Result )

20import Rel8.Table.Either ( EitherTable )

23-- | Nest an 'Either' value within a 'Rel8able'. @HEither f a b@ will produce a

24-- 'EitherTable' @a b@ in the 'Expr' context, and a 'Either' @a b@ in the

25-- 'Result' context.

26type HEither :: K.Context -> Type -> Type -> Type

27type family HEither context = either | either -> context where

28 HEither Aggregate = EitherTable Aggregate

29 HEither Expr = EitherTable Expr

30 HEither Name = EitherTable Name

31 HEither Result = Either