src/Rel8/Expr/Function.hs · rel8

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rel8/src/Rel8/Expr/Function.hs

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1{-# language FlexibleContexts #-}

2{-# language FlexibleInstances #-}

3{-# language MultiParamTypeClasses #-}

4{-# language StandaloneKindSignatures #-}

5{-# language TypeFamilies #-}

6{-# language UndecidableInstances #-}

8module Rel8.Expr.Function

9 ( Function, function

10 , nullaryFunction

11 , binaryOperator

12 )

13where

15-- base

16import Data.Kind ( Constraint, Type )

17import Prelude

19-- opaleye

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

22-- rel8

23import Rel8.Expr ( Expr( Expr ) )

24import Rel8.Expr.Opaleye

25 ( castExpr

26 , fromPrimExpr, toPrimExpr, zipPrimExprsWith

27 )

28import Rel8.Schema.Nullability ( Nullabilizes )

29import Rel8.Type ( DBType )

32type Function :: Type -> Type -> Constraint

33class Function arg res where

34 applyArgument :: ([Opaleye.PrimExpr] -> Opaleye.PrimExpr) -> arg -> res

37instance (arg ~ Expr a, DBType db, Nullabilizes db b) => Function arg (Expr b)

38 where

39 applyArgument f a = castExpr $ fromPrimExpr $ f [toPrimExpr a]

42instance (arg ~ Expr a, Function args res) => Function arg (args -> res) where

43 applyArgument f a = applyArgument (f . (toPrimExpr a :))

46function :: Function args result => String -> args -> result

47function = applyArgument . Opaleye.FunExpr

50nullaryFunction :: (DBType db, Nullabilizes db a) => String -> Expr a

51nullaryFunction name = castExpr $ Expr (Opaleye.FunExpr name [])

54-- | Construct an expression by applying an infix binary operator to two

55-- operands.

56binaryOperator :: (DBType db, Nullabilizes db c)

57 => String -> Expr a -> Expr b -> Expr c

58binaryOperator operator a b =

59 castExpr $ zipPrimExprsWith (Opaleye.BinExpr (Opaleye.OpOther operator)) a b