src/Rel8/Column.hs · rel8

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rel8/src/Rel8/Column.hs

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1{-# language DataKinds #-}

2{-# language StandaloneKindSignatures #-}

3{-# language TypeFamilies #-}

5module Rel8.Column

6 ( Column

7 , TColumn

8 )

9where

11-- base

12import Data.Kind ( Type )

13import Prelude ()

15-- rel8

16import Rel8.FCF ( Eval, Exp )

17import qualified Rel8.Schema.Kind as K

18import Rel8.Schema.Context.Lower ( Lower )

19import Rel8.Schema.Result ( Result )

22-- | This type family is used to specify columns in 'Rel8able's. In @Column f

23-- a@, @f@ is the context of the column (which should be left polymorphic in

24-- 'Rel8able' definitions), and @a@ is the type of the column.

25type Column :: K.Context -> Type -> Type

26type family Column context a where

27 Column Result a = a

28 Column context a = Lower context a

31data TColumn :: K.Context -> Type -> Exp Type

32type instance Eval (TColumn f a) = Column f a