This is the start of a solution in Haskell: import System.Environment import qualified Data.Vector.Unboxed as V import Data.Vector.Unboxed (Vector)

This is the start of a solution in Haskell: import System.Environment import qualified Data.Vector.Unboxed as V import Data.Vector.Unboxed (Vector) display :: Vector Double -> String display ds | V.null ds = "" | otherwise = tail . concatMap format . V.toList $ ds where format d = ',' : show d csv_sums :: String -> Vector Double csv_sums input = go (V.length $ h) 1 h t where h : t = map (V.fromList . read . bracket) $ lines input bracket s = '[' : s ++ "]" go s n summary [] = summary go s n summary (x:xs) | V.length x == s = go s (n + 1) (V.zipWith (+) summary x) xs | otherwise = if blankLastLine then summary else error "Inconsistent lengths." where blankLastLine = case xs of [] -> V.length x == 0 _ -> False main = do paths <- getArgs if length paths /= 1 then error "Exactly one filename must be given." else readFile (head paths) >>= putStrLn . display . csv_sums It takes about 22x longer than Python on my platform though, which I'm not sure how to solve. (The vector keeps it nice and un-thunked so it doesn't seem like it's laziness that's killing it, maybe it's the use of strings over Data.ByteString.Lazy or so?)