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.Aggregate ( Aggregate )

17import Rel8.Expr ( Expr )

18import Rel8.FCF ( Eval, Exp )

19import qualified Rel8.Schema.Kind as K

20import Rel8.Schema.Name ( Name(..) )

21import Rel8.Schema.Result ( Result )

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

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

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

27type Column :: K.Context -> Type -> Type

28type family Column context a where

29 Column Aggregate a = Aggregate a

30 Column Expr a = Expr a

31 Column Name a = Name a

32 Column Result a = a

35data TColumn :: K.Context -> Type -> Exp Type

36type instance Eval (TColumn f a) = Column f a