同じ型を持つオブジェクトの実装を変えられるようにしたい

自律機能を備えたAutonomie
Characterを生成するときにどうやって動くか(runAuto の実装)を選ぶことができる

キャラクタによってmoveの実装をわけたいときなどに便利(おそらくもう少し一般化可能)

{-# LANGUAGE TemplateHaskell, TypeSynonymInstances, FlexibleInstances #-}
import Control.Monad.State
import Control.Lens
import Data.Functor.Identity

data Autonomie m a = Autonomie { auto :: a, runAuto :: m () }

class Game c where
  update :: State c ()
  draw :: StateT c IO ()

data Object = Object { _pos :: (Int, Int) }
makeClassy ''Object

type Character = Autonomie (State Object) Object
instance HasObject Character where
  object = lens auto (\f a -> Autonomie a (runAuto f))

instance Game Character where
  update = do
    f <- get
    object %= execState (runAuto f)
  draw = do
    f <- get
    lift $ print $ f^.pos

walk :: State Object ()
walk = pos %= (\(x,y) -> (x+2, y))

dash :: State Object ()
dash = pos %= (\(x,y) -> (x+10, y))

main = do
  let chara1 = Autonomie (Object (100, 100)) walk
  draw `execStateT` (update `execState` chara1)
  
  let chara2 = Autonomie (Object (100, 100)) dash
  draw `execStateT` (update `execState` chara2)