I have a series of NxM numeric tables I'm doing a quick mean/variance/t-test etcetera on. The cell t1 [i,j] corresponds exactly to the cells t2..N [i,j], and so it's perfectly possible to read one item at a time from each of the 100 files and compute the mean/variance etcetera on all cells that way. So what I propose to do is something along the lines of: openAndProcess filename = f <- readFile filename return (map (L.split ',') . lines $ f) main = do fs <- getArgs let items = map (map read) . map openAndProcess fs in do print . map (map $ mean) items print . map (map $ variance) items How close am I to doing the right thing here? As I understand it, this will result in one hundred IO [String] instances being returned by the call to (map openAndProcess $ filenames). Do I need to do something special to lift (read), (mean), and (variance), or even (map) into the IO monad so they can process the input as needed? Thanks in advance, -- Jeff