Q: When trying to compose the following IO actions: readFile fileName >>= \ contents -> writeFile fileName (f contents) I get an exception: openFile: permission denied. However the following works: readFile fileName >>= \ contents -> (mapM_ putStrLn . lines) contents >> writeFile fileName (f contents) I'm assuming it has something to do with lazy IO, and the second action in the second version forces fileName to be read completely and to be closed. Why do I need to do that? I thought lazy IO was implemented in such a way that you were safe to INTERPRET the IO action as having been fully performed. (And so I would have been safe to interpret that, in the first version, in the first action, the file was released.) If that's not the case, then: (1) What is the proper way to reason about lazy IO? (2) Is there some action less arbitrary that what I cooked up in the second version that explicitly instructs to release a file or some other resource? Regards, Jacek.