This is probably a FAQ of sorts, but I found composing the proper search terms complicated. When I write simple parsers and the like I tend to prefer returning useful error strings instead of simply Nothing from Maybe. For example this is a common utility function of mine. Yes, I know with the addition of a Read n qualification I can make this more generic but it does not help with the current discussion. getNum :: String -> Either String Int getNum n = case reads n of [(x, "")] -> Right x [(x, cs)] -> Left $ "incomplete parse: " ++ cs cs -> Left $ "invalid number: " ++ cs But I would rather write the following so I am not bound to Either. This would even work with Maybe since Nothing just drops the string from fail. getNum :: Monad m => String -> m Int getNum n = case reads n of [(x, "")] -> return x [(x, cs)] -> fail $ "incomplete parse: " ++ cs cs -> fail $ "invalid number: " ++ cs Yeah, I know, no one likes the fact that fail raises an exception. What I would like to do in my code is define something like class (Monad a) => MonadGentle a where myreturn = return myfail s = fails s But I can not get an instance of this to compile because it insists myreturn and myfail are not visible. Since this comes up a lot in the tutorials and books, I am curious why there is not something like MonadGentle in Hackage or the libs. I use mzero occasionally, but as I said I usually prefer some information with my errors since it makes for more human usable results. Thanks.