I wonder whether the Ord instance is a good choice as constraint for
Data.Map, Data.Set and so on. I want to manage complex numbers and residue
classes in a set, or polynomials as keys of maps, but I hesitate to make
them instances of Ord, because "a Indexable a where
compareIndex :: a -> a -> Ordering
then make several mathematical object types instances of this class. Then
make a wrapper type
newtype IndexableToOrd a = Cons a
which maps the Indexable instance to an Ord instance:
instance Indexable a => Ord (IndexableToOrd a) where
compareIndex (Cons x) (Cons y) = compare x y
Then I do not insert complex numbers immediately in a set, but wrap them
in IndexableToOrd and insert the wrapped values in a set.
Cumbersome, isn't it? So my question is: Was the Ord constraint for
Data.Map a good idea? If yes, are there simpler work-arounds than mine?
I think, that '<' and '>' imply something like comparisons of magnitudes
and the Data.Map doesn't require that notion and it is happy with any
total ordering.
Btw. is there a Data.Map.unzip?
