This isn't two functions: it's actually one function defined by cases. You can think of it as equivalent to fn x y = case (x, y) of (Just q, Just z)

This isn't two functions: it's actually one function defined by cases. You can think of it as equivalent to fn x y = case (x, y) of (Just q, Just z) -> q + z (_, _) -> 0 but the case becomes implicit in the repetition of the function name at the top level of indentation.