Re: [Haskell-beginners] Further constraining types

Once you've validated your user input though, nothing prevents you to have it return a Positive Int that you will guarantee can hold only positive integers, for example by using a smart constructor, and hiding the contructor in a separate module. You don't need dependant types for this.

Yes, but once you want to operate on that data you'll note the difference: subtract :: Positive Int -> Positive Int -> ??? IIUC with dependent types you'll have a compile time guarantee, without you'll have to test for errors at runtime. Regards, Thomas