Data.Map, Data.Set working together

[Ketil Malde]

I need to search intervals -- i.e. I'd like to store integer keys, and
looking up any integer should return the largest key less than my
query.  (Ideally with it's associated datum, but that could of course
be stored in a separate map).

Do any of the set/map implementations support this?

-kzm
-- 
If I haven't seen further, it is by standing in the footprints of giants