[Haskell-cafe] MonadFail with type parameter for error message

Dear Cafe, MonadFail.fail takes String. I wasn't able to find MonadFail for custom error type. Is there any proposals to base? Let's say Data.Text, which gains popularity with OverloadedStrings extensions. class MonadFail m where fail :: String -> m a Why not ? class MonadFail m where fail :: (forall s. IsString s => s) -> m a class MonadFailWith m s where fail :: s -> m a -- Best regards, Daniil Iaitskov