Hello I recently noticed that Data.HashTable silently accepts duplicate keys and keeps all the values. This is very counterintuitive from the interface and makes updating a hashtable quite tedious (lookup + delete + insert). Mentioning the feature in the documentation and providing an update function would be very nice. e.g. update :: HashTable k v -> k -> (v -> v) -> IO Bool or update :: HashTable k v -> k -> (v -> (v, w)) -> IO (Maybe w) with the result marking whether the key was present in the hashtable. On the other hand, if it is a bug I hope it will be solved quickly. The behaviour can be demonstrated with main = do ht <- new (==) hashInt insert ht 1 1 insert ht 1 2 toList ht >>= print - Einar Karttunen