src/Rel8/Order.hs · rel8

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rel8/src/Rel8/Order.hs

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1{-# language DerivingStrategies #-}

2{-# language GeneralizedNewtypeDeriving #-}

3{-# language StandaloneKindSignatures #-}

5module Rel8.Order

6 ( Order(..)

7 , toOrderExprs

8 )

9where

11-- base

12import Data.Functor.Contravariant ( Contravariant )

13import Data.Kind ( Type )

14import Prelude

16-- contravariant

17import Data.Functor.Contravariant.Divisible ( Decidable, Divisible )

19-- opaleye

20import qualified Opaleye.Internal.HaskellDB.PrimQuery as Opaleye

21import qualified Opaleye.Internal.Order as Opaleye

24-- | An ordering expression for @a@. Primitive orderings are defined with

25-- 'Rel8.asc' and 'Rel8.desc', and you can combine @Order@ via its various

26-- instances.

28-- A common pattern is to use '<>' to combine multiple orderings in sequence,

29-- and '>$<' (from 'Contravariant') to select individual columns.

30type Order :: Type -> Type

31newtype Order a = Order (Opaleye.Order a)

32 deriving newtype (Contravariant, Divisible, Decidable, Semigroup, Monoid)

35toOrderExprs :: Order a -> a -> [Opaleye.OrderExpr]

36toOrderExprs (Order (Opaleye.Order order)) a =

37 uncurry Opaleye.OrderExpr <$> order a