Question

I need this function:

blubb :: ??? -> Int
blubb (n :: Int) = n
blubb (n :: Char) = 42

This is how it should work: the function gets an Int and returns it. If the function gets an Char it returns a constant value and the other cases are indifferent.

Because of the type system in Haskell it might be not possible but I need to get this working …

Answer 1

This is what type classes are for:

class Blubb t where
    blubb :: t -> Int


instance Blubb Int where
    blubb n = n

instance Blubb Char where
    blubb _ = 42

This overloads blubb to work on both Ints and Chars. The compiler will select the correct one to use based off of the type of the argument.

However, be careful that you are not using type classes where you actually wanted an Either. You may have actually wanted this:

blubb :: Either Int Char -> int
blubb (Left  n) = n
blubb (Right _) = 42