instance (Ord a, Ord b) => Ord (a,b) where compare (x,y) (z,w) = case compare x z of EQ -> compare y w c -> c Not certain that's the exact code that's used, but it's close enough. Bob On 11 Jul 2009, at 15:06, Patrick LeBoutillier wrote:

Hi,

I see the type of the List.sort function is:

Ord a => [a] -> [a]

I don't understand how this type can allow it to sort pairs:

Prelude> :m +List Prelude List> sort [(1, "1"), (3, "3"), (2, "2")] [(1,"1"),(2,"2"),(3,"3")]

How can a pair by of type "Ord a"? Is it a rule that the first element is automatically used?

Patrick

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