Not completely! This is a possible implementation:
case insertLookupWithKey (\_ -> Set.union) k (Set.singleton v) chart of
(Nothing, chart) -> Just chart
(Just set, chart) | Set.member v set -> Nothing
| otherwise -> Just chart
but notice that the set is still traversed twice.
On Tue, Jun 3, 2008 at 12:07 AM, Neil Mitchell
Hi Krasimir,
insert :: k -> v -> Chart k v -> Maybe (Chart k v)
where the result is (Just _) if the (k,v) is actually added to the chart or Nothing if it was already there and nothing have to be done.
insertLookupWithKey :: Ord k => (k -> a -> a -> a) -> k -> a -> Map k a -> (Maybe a, Map k a)
This should provide the information you need, without the double traversal of the data structure.
Thanks
Neil