src/Rel8/Query.hs · rel8

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rel8/src/Rel8/Query.hs

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1{-# language DerivingVia #-}

2{-# language GeneralizedNewtypeDeriving #-}

3{-# language StandaloneKindSignatures #-}

5module Rel8.Query

6 ( Query( Query )

7 )

8where

10-- base

11import Data.Kind ( Type )

12import Prelude

14-- opaleye

15import qualified Opaleye.Select as Opaleye

17-- rel8

18import Rel8.Query.Set ( unionAll )

19import Rel8.Query.Values ( values )

20import Rel8.Table.Alternative

21 ( AltTable, (<|>:)

22 , AlternativeTable, emptyTable

23 )

25-- semigroupoids

26import Data.Functor.Apply ( Apply, WrappedApplicative(..) )

27import Data.Functor.Bind ( Bind, (>>-) )

30-- | The @Query@ monad allows you to compose a @SELECT@ query. This monad has

31-- semantics similar to the list (@[]@) monad.

32type Query :: Type -> Type

33newtype Query a = Query (Opaleye.Select a)

34 deriving newtype (Functor, Applicative, Monad)

35 deriving Apply via (WrappedApplicative Opaleye.Select)

38instance Bind Query where

39 (>>-) = (>>=)

42-- | '<|>:' = 'unionAll'.

43instance AltTable Query where

44 (<|>:) = unionAll

47-- | 'emptyTable' = 'values' @[]@.

48instance AlternativeTable Query where

49 emptyTable = values []