Why sum x y is of type (Num a) => a -> a -> a in Haskell?

Question

I\'ve been reading about Haskell and I\'m having a hard time understanding how function definitions are handled in this language.

Let\'s say I\'m defining a su

Answer 1

The Haskell documentation isn't too clear about it, but (Num a) => means that the function works for all cases where a is a Num or derives from it (therefore is a number).

Also see: http://www.cse.unsw.edu.au/~en1000/haskell/inbuilt.html