https://stackoverflow.com/questions/55110643/haskell-readert-design-pattern-vs-mtl-statet-pattern

uses-rio.hs

#!/usr/bin/env stack
-- stack --resolver lts-12.21 script
{-# LANGUAGE NoImplicitPrelude #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE TemplateHaskell #-}

import           Control.Lens
import           Control.Monad (replicateM)
import           System.Random
import           RIO

data PlayerState = PlayerState {
  _psName  :: String,
  _psScore :: Int
                               } deriving (Show)

makeClassy ''PlayerState

data Game = Game {
  _turns   :: Int,
  _players :: [PlayerState]
                 } deriving (Show)

makeClassy ''Game

randomGameInit :: IO Game
randomGameInit = do
  players <- replicateM 5 $  PlayerState <$> (replicateM 4 $ randomRIO ('a', 'z')) <*> randomRIO (1,10)
  return $ Game 0 players

update :: (HasStateRef s env, HasGame s) => RIO env ()
update = do
  players . ix 0 . psName %= (\_ -> "mordor")
  turns %= (+1)
  exitCondition <- fmap (>10) (turns <%= id)
  unless exitCondition update

main :: IO ()
main = do
  init <- randomGameInit >>= newSomeRef
  runRIO init update >> runSimpleApp (logInfo "Game Over")