> I'd expect some kind of expection in that case. Sorry, what exactly do you mean by ‘expectation’ here? > This sounds like a dangerous example of monads (sin

> I'd expect some kind of expection in that case. Sorry, what exactly do you mean by ‘expectation’ here? > This sounds like a dangerous example of monads (since you don't know if you had a Nothing value up in the chain or a valid value that can't be representated)! Well, this particular case is of course oversimplified. There’s plenty of ways of dealing with different kinds of errors. The easiest is to define a sum type of errors: data DivisionError = ValueMissing | NonIntegralValue Then redefine the function to return an ‘Either DivisionError Int’: half x | even x = Right (x `div` 2) | otherwise = Left NonIntegralValue Now chaining several calls to ‘half’ will abort at the first error.