无法在ReaderT包装中推导MonadReader

newtype ReaderT r m a = ReaderT { runReaderT :: r -> m a }

import Control.Monad.Reader

type MyReader a = ReaderT Env IO a

runMyReader :: MyReader a -> Env -> IO a
runMyReader = runReaderT

data Env = Env { config :: String }

example :: MyReader String
example = do
  cfg <- asks config
  return ("Config: " ++ cfg)

import cats._
import cats.data._
import cats.implicits._

case class Env(config: String)

type MyReader[A] = ReaderT[IO, Env, A]

implicit val monadReaderInstance: MonadReader[Env, MyReader] = new MonadReader[Env, MyReader] {
  def ask: MyReader[Env] = ReaderT.ask[IO, Env]
  def local[A](f: Env => Env)(fa: MyReader[A]): MyReader[A] = ReaderT.local[IO](f)(fa)
}

import Control.Monad.Reader

type MyReader a = ReaderT Env IO a

runMyReader :: MyReader a -> Env -> IO a
runMyReader = runReaderT

data Env = Env { config :: String }

example :: MyReader String
example = do
  cfg <- asks config
  return ("Config: " ++ cfg)

main :: IO ()
main = do
  let env = Env "exampleConfig"
  result <- runMyReader example env
  putStrLn result