{-# LANGUAGE DataKinds #-}
{-# LANGUAGE GADTs #-}
{-# LANGUAGE LambdaCase #-}
{-# LANGUAGE StandaloneDeriving #-}
{-# LANGUAGE TypeApplications #-}
{-# LANGUAGE TypeFamilies #-}
module Main where

import qualified Data.Dependent.EnumMap.Strict as DE
import Data.Dependent.Sum
import Data.Some


data Tag = A | B | C
  deriving (Show)

data STag tag where
  SA :: STag A
  SB :: STag B
  SC :: STag C
deriving instance Show (STag tag)

instance DE.Enum1 STag where
  type Enum1Info STag = ()
  fromEnum1 = \case { SA -> (0, ()); SB -> (1, ()); SC -> (2, ()) }
  toEnum1 n () = case n of { 0 -> Some SA; 1 -> Some SB; 2 -> Some SC; _ -> error "invalid tag" }

data Value tag where
  VA :: Int -> Value A
  VB :: Bool -> Value B
  VC :: String -> Value c
deriving instance Show (Value tag)


main :: IO ()
main = do
  print $ DE.fromList @STag @Value []
  print $ DE.fromList [SB :=> VB False, SA :=> VA 3]