[Haskell-beginners] Why isn't :t (1+1) Integer

Hi, i read that the default type for Num is Integer. If we specify a type for one of the arguments: :t (1 + 1::Double) is Double If we don't, i expect the default type for Num to come into play: However :t (1 + 1) is Num a => a Why is that so? -- Best Regards, Boon Hui