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

[Michael Snoyman]

On Tue, Jul 12, 2011 at 7:20 PM, Dan Ross <dan at rosspixelworks.com> wrote:
> 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!"

Hi Dan,

The first version is polymorphic, and will work on *any* instance of
Integral. This would allow people to use Int, Int32, Int64, etc. The
second version requires the user to pass in specifically an Integer.

Michael