Return specific type within Haskell

Question

I have a pretty general question about Haskell\'s type system. I\'m trying to become familiar with it, and I have the following function:

getN :: Num a =>         


        

Answer 1

To add to sth's answer: Haskell is not object-oriented. It's not true that Double is a subclass of Num, so you cannot return a Double if you promise to return a polymorphic Num value, like you can in, say, Java.

When you write getN :: Num a => a you promise to return a value that is fully polymorphic within the Num constraint. Effectively this means that you can only use functions from the Num type class, such as +, *, - and fromInteger.