I'm trying to define a polymorphic "add" function which takes a variable number of arguments (instance of Num) and returns their sum. I don't want to specify the types of the arguments while calling the function, I just want to , at most, specify the return type (it should infer that the return type is the type of the arguments).

class Add a b where
    add :: a -> b

instance Num a => Add a a where
    add = id

instance (Num a, Add a b) => Add (a -> b) where
    add x y = add (x + y)

Can someone tell me why this is not working and propose a fix for this, if possible?

Thanks in advance