Hello, I am writing a program which scans a bunch of directories to detect changes (added, modified, deleted files). To detect modification, I would like to use getModification, doing something like the following: -- |Stores last modified timestamp of the file -- Yes, I come from Java... type HashMap = M.Map FilePath ClockTime data (Show a, Eq a) => Edit a = Mod a | Add a | Del a deriving (Eq,Show) checkChanges :: [String] -> HashMap -> IO ([Edit FilePath], HashMap) checkChanges [fs] m = do addedFilesList <- lsRecursive fs timestamps <- mapM getModificationTime addedFilesList let allts = zip addedFilesList timestamps let ret = (findDeletedFiles allts.updateScannedFiles allts) ([],m) return ret -- | Returns an updated map and a list of modified/added/deleted files updateScannedFiles :: [(FilePath,ClockTime)] -> ([Edit FilePath], HashMap) -> ([Edit FilePath], HashMap) updateScannedFiles [] r = r updateScannedFiles ((path,ts):files) (updates,m) = case M.lookup path m of Nothing -> updateScannedFiles files ((Add path:updates), M.insert path ts m) Just ts' -> if ts' < ts then updateScannedFiles files ((Mod path:updates), M.adjust (const ts) path m) else updateScannedFiles files (updates, m) -- omitting findDeletedFiles which is obvious and works I got the following test case that fails: "recursively marks changed files as modified" `for` do complexFileSetup -- create a small FS tree with 3 files root <- tempDir state <- checkChanges [root] M.empty writeFile (root "subdir" "cFile.txt") "this is another toast" checkChanges [root] (snd state) >>= (\r -> assertEqual "there should be 1 changed file in 3 files" 1 ((length.modified.fst) r)), In words: the getModificationTime of the overwritten file appears identical before and after the write. What am I doing wrong ? BTW, I checked the content of the file which has been correctly updated. Thanks for your help Arnaud