什么是GHCi的MonadError默认实现？

class Monad m => MonadError e m | m -> e where
  throwError :: e -> m a
  catchError :: m a -> (e -> m a) -> m a

import Control.Monad.Error.Class (throwError, catchError)
import System.IO.Error (IOError, ioError)

readFile' :: FilePath -> IO (Either IOError String)
readFile' path = readFile path `catchError` \e -> return (Left e)

writeFile' :: FilePath -> String -> IO (Either IOError ())
writeFile' path content = writeFile path content `catchError` \e -> return (Left e)

main :: IO ()
main = do
  result <- readFile' "nonexistent.txt"
  case result of
    Left e -> putStrLn $ "Error: " ++ show e
    Right content -> putStrLn content

  result' <- writeFile' "output.txt" "Hello, world!"
  case result' of
    Left e -> putStrLn $ "Error: " ++ show e
    Right () -> putStrLn "File written successfully."