I'm currently improving Data.Map documentation. Behavior of updateAt in this module differs from what I would expect. The documentation says: updateAt :: (k -> a -> Maybe a) -> Int -> Map k a -> Map k a O(log n). Update the element at index. Calls error when an invalid index is used. So I expected this code: let m = fromList [(3,"b"),(5,"a")] let f k a = Just "x" updateAt f 1 m to return fromList [(3,"b"),(5,"x")] but it returns fromList [(5,"x")] deleting the key 3. I tested this using ghci 6.6. Is this a bug or I missed something here? Thanks, Andriy ____________________________________________________________________________________ Fussy? Opinionated? Impossible to please? Perfect. Join Yahoo!'s user panel and lay it on us. http://surveylink.yahoo.com/gmrs/yahoo_panel_invite.asp?a=7