src/Rel8/Column/Maybe.hs · rel8

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1{-# language DataKinds #-}

2{-# language StandaloneKindSignatures #-}

3{-# language TypeFamilyDependencies #-}

5module Rel8.Column.Maybe

6 ( HMaybe

7 )

8where

10-- base

11import Data.Kind ( Type )

12import Prelude

14-- rel8

15import qualified Rel8.Schema.Kind as K

16import Rel8.Schema.Result ( Result )

17import Rel8.Table.Maybe ( MaybeTable )

20-- | Nest a 'Maybe' value within a 'Rel8able'. @HMaybe f a@ will produce a

21-- 'MaybeTable' @a@ in the 'Expr' context, and a 'Maybe' @a@ in the 'Result'

22-- context.

23type HMaybe :: K.Context -> Type -> Type

24type family HMaybe context = maybe | maybe -> context where

25 HMaybe Result = Maybe

26 HMaybe context = MaybeTable context