[Haskell-cafe] Pattern matching on numbers?

How does this work?

fac n = case n of 0 -> 1 _ -> n * fac (n-1)

ghci> :t fac fac :: (Num t) => t -> t The first line of "fac" pattern matches on 0. So how does this work over any value of the Num typeclass? I know that the "1" on the rhs of fac are replaced with (fromInteger 1), but what about numeric literals in patterns? Does it turn into a call to (==)? Should whatever technique is used be extended to other typeclasses too? -- ryan