{-# LANGUAGE TypeFamilies, DataKinds, GADTs, RankNTypes, UndecidableInstances #-}

module DatascriptExample () where

import Data.Proxy (Proxy(..))

type Id = Int

data Attribute = StringAttribute | IntAttribute
data Cardinality = One | Many

type family AttributeType (attr :: Attribute)
type instance AttributeType StringAttribute = String
type instance AttributeType IntAttribute = Int

type family CardinalityType (card :: Cardinality) r
type instance CardinalityType One r = r
type instance CardinalityType Many r = [r]

type family ValueType (attr :: Attribute) (card :: Cardinality)
type instance ValueType attr card = CardinalityType card (AttributeType attr)

data DAtom where
  Entry :: forall (attr :: Attribute) (card :: Cardinality) . Id -> Proxy attr -> Proxy card -> ValueType attr card -> DAtom

example1 :: DAtom
example1 = Entry 0 (Proxy :: Proxy StringAttribute) (Proxy :: Proxy Many) ["adf", "asdf"]

example2 :: DAtom
example2 = Entry 0 (Proxy :: Proxy IntAttribute) (Proxy :: Proxy One) 10