"Simon Marlow" <[EMAIL PROTECTED]> writes: > > > -- | add data from a file to the histogram > > > addFile :: FiniteMap String Int -> String -> IO (FiniteMap > > String Int) > > > addFile fm name = do > > > x <- readFile name > > > return (addHist fm x) > > > > > > -- | add data from all files in a directory to the histogram > > > addDir :: FiniteMap String Int -> String -> IO (FiniteMap > > String Int) > > > addDir fm dir = do > > > dc <- getDirectoryContents dir > > > fs <- filterM doesFileExist (map ((dir++"/")++) dc) > > > foldM addFile fm fs
> It's not possible to tell from this code whether the readFiles will be > fully evaluated or not: it depends on how much evaluation addHist does, > and to what extend the result FiniteMap is demanded, amongst other > things. Of course. Never cut code, I suppose; I thought the parts my understanding would be weakest would be the monadic stuff, not this: > addHist :: FiniteMap String Int -> String -> FiniteMap String Int > addHist fm = foldl add1 fm . words > where add1 f w = > case lookupFM f w of > Just n -> addToFM f w (n+1) > Nothing -> addToFM f w 1 I felt pretty sure that this would evaluate the string to the end. Am I wrong? > These things are always tricky to understand, which is why I recommend > not using lazy I/O. File reading is not a pure operation: running out > of file descriptors is a good counter-example. Okay. Perhaps renaming "readFile" to "unsafeReadFile"? :-) -kzm -- If I haven't seen further, it is by standing in the footprints of giants _______________________________________________ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
