{-# LANGUAGE DataKinds #-}
{-# LANGUAGE GADTs #-}
{-# LANGUAGE GHC2021 #-}
module Main where

data Mode = A | B
data Settings (m :: Mode) where
    SettingsA :: Int -> Settings A
    SettingsB :: String -> Settings B

data State (m :: Mode) where
    AState :: Double -> State A
    BState :: Float -> State B

makeItHappen :: Settings m -> State m -> State m
makeItHappen settings state =
  let newState = case state of
        AState x ->
          case settings of
            SettingsA i -> AState (x + fromIntegral i)
        BState x ->
          case settings of
            SettingsB i -> BState (x + read i)
   in newState

main :: IO ()
main = do
  putStrLn "done."