src/Rel8/Query.hs · rel8

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rel8/src/Rel8/Query.hs

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1{-# language DerivingStrategies #-}

2{-# language DerivingVia #-}

3{-# language GeneralizedNewtypeDeriving #-}

4{-# language StandaloneKindSignatures #-}

6module Rel8.Query

7 ( Query( Query )

8 )

9where

11-- base

12import Data.Kind ( Type )

13import Prelude

15-- opaleye

16import qualified Opaleye.Select as Opaleye

18-- rel8

19import Rel8.Query.Set ( unionAll )

20import Rel8.Query.Values ( values )

21import Rel8.Table.Alternative

22 ( AltTable, (<|>:)

23 , AlternativeTable, emptyTable

24 )

26-- semigroupoids

27import Data.Functor.Apply ( Apply, WrappedApplicative(..) )

28import Data.Functor.Bind ( Bind, (>>-) )

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

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

33type Query :: Type -> Type

34newtype Query a = Query (Opaleye.Select a)

35 deriving newtype (Functor, Applicative, Monad)

36 deriving Apply via (WrappedApplicative Opaleye.Select)

39instance Bind Query where

40 (>>-) = (>>=)

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

44instance AltTable Query where

45 (<|>:) = unionAll

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

49instance AlternativeTable Query where

50 emptyTable = values []