ReaderT config (StateT state Identity)

{-# LANGUAGE GeneralizedNewtypeDeriving #-}

import Control.Monad.Trans
import Control.Monad.Trans.State
import Control.Monad.Trans.Reader
import Control.Monad.Identity
import qualified Control.Monad.State as S
import qualified Control.Monad.Reader as R


data AppState = AppState Int deriving Show
data AppConfig = AppConfig String deriving Show

type App = ReaderT AppConfig (StateT AppState Identity)


app :: App String
app = do
  (AppConfig config) <- ask
  (AppState st) <- lift S.get
  S.put (AppState $ st + 1)
  return $ config ++ " " ++ show st

runApp :: App a -> String -> Identity (a, AppState)
runApp app conf =
    let config = AppConfig conf
        state = AppState 0
    in runStateT (runReaderT app config) state

-- runIdentity $ runApp app "a"


---


newtype MyApp a = MyA {
  runA :: ReaderT AppConfig (StateT AppState Identity) a
} deriving (Functor, Applicative, Monad, R.MonadReader AppConfig, S.MonadState AppState)

myApp :: MyApp String
myApp = do
  (AppConfig config) <- R.ask
  (AppState st) <- S.get
  S.put (AppState $ st + 1)
  return $ config ++ " " ++ show st

runMyApp :: MyApp a -> String -> Identity (a, AppState)
runMyApp k maxDepth =
    let config = AppConfig maxDepth
        state = AppState 0
    in runStateT (runReaderT (runA k) config) state
    
-- runIdentity $ runMyApp myApp "hello"

---

main = do
  print $ runIdentity $ runApp app "hello"
  print $ runIdentity $ runMyApp myApp "hello"