John Meacham wrote:
1. one really does logically derive from the other, Eq and Ord are like this, the rules of Eq says it must be an equivalance relation and that Ord defines a total order over that equivalance relation. this is a good thing, as it lets you write code that depends on these properties.
given an Ord instance (for a type T) a corresponding Eq instance can be given by: instance Eq T where a == b = compare a b == EQ This does not make the definition of an Ord instance (that is supposed to match an equivalence) easier but ensures at least the required consistency. I never dared to define this generically and switch on various ghc extensions: instance Ord a => Eq a where ... It just strikes me that wrt. "NaN" the Ord instances for Float and Double are no total orders (and thus these types are not suited for sets, i.e. "Data.Set.Set Float") Cheers Christian