Something something - to add type signatures or not to add type signatures...

Rurder.hs

newtype AppM a = AppM (Env -> IO a)

instance Functor AppM where
  fmap = error "fmap for AppM not implemented"

instance Applicative AppM where
  pure  = error "pure for AppM not implemented"
  (<*>) = error "ap for AppM not implemented"

instance Monad AppM where
  return = error "return for AppM not implemented"
  (>>=)  = error "bind for AppM not implemented"

instance MonadIO AppM where
  liftIO = error "liftIO for AppM not implemented"

instance MonadReader Env AppM where
  ask    = error "ask for AppM not implemented"
  local  = error "local for AppM not implemented"
  reader = error "reader for AppM not implemented"