[Haskell-beginners] (Integral a) => a vs Integer

Hi all- I'm going through Learn You a Haskell for Great Good and I don't understand the advantage of using (Integral a)=> a vs just Integer as I show below. Could someone explain this to me? Thanks, Dan lucky :: (Integral a) => a -> String lucky 7 = "LUCKY NUMBER SEVEN!" lucky x = "Sorry, you're out of luck, pal!" lucky :: Integer -> String lucky 7 = "LUCKY NUMBER SEVEN!" lucky x = "Sorry, you're out of luck, pal!"