"Ketil Z. Malde" wrote: > "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?
The string won't be evaluated until the finite map is demanded. None of the code you've shown so far makes that demand. -- Dean _______________________________________________ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
