The interfaces from Data.IntMap and Data.Map are subtly different. Here are two issues: 1. deleteMin/Max raise an exception on empty maps/set > Data.Map.deleteMax Data.Map.empty fromList [] > Data.IntMap.deleteMax Data.IntMap.empty fromList *** Exception: deleteMax: empty map has no maximal element > Data.Set.deleteMin Data.Set.empty fromList [] > Data.IntSet.deleteMin Data.IntSet.empty fromList *** Exception: deleteMin: empty set has no minimal element Proposal: Data.IntMap/IntSet.deleteMin/Max should return empty when the input is empty. 2. findMin/Max have a different signature Data.Map.findMin :: Map k a -> (k, a) Data.IntMap.findMin :: IntMap a -> a The documentation of IntMap.findMin is also incorrect, it reads: /O(log n)/ The minimal key of the map. While it returns the value associated with the minimal key. Proposal: Data.IntMap.findMin/findMax should have the type IntMap a -> (Key,a) Twan