Hi, For the code below, where it says "HERE" in comments, if I remove the part after `using` the code works fine. However, with this version it causes a Stack space overflow (if allowed uses GBs of memory). You just need to input a file with around 1M lines each having something like "Int Value: 3 @x". What is wrong with adding the parList to this code? (Same thing happens for parMap, and parListChunk, etc) Yavuz import System.IO import System.Environment import System.IO.Error import Control.Parallel import Control.Parallel.Strategies import Control.Monad import Data.Binary as DB import Data.Binary.Put import Data.Word import Data.Maybe import qualified Data.ByteString.Lazy as B import Text.Regex.TDFA import Text.Regex.Base.Context main = do { args <- getArgs; x <- getLines (head args); mapM_ writeMaybeIntBinary ((map perLineOperator x) `using` parList rdeepseq); -- HERE return (); } writeMaybeIntBinary :: Maybe Word32 -> IO () writeMaybeIntBinary Nothing = return (); writeMaybeIntBinary (Just intB) = do { B.hPut stdout (runPut (putWord32host intB));}; getLines :: FilePath -> IO [String] getLines = liftM lines . readFile perLineOperator :: String -> Maybe Word32 perLineOperator line = let { getIntStr :: String -> String; getIntStr "" = ""; getIntStr line = let { matches = (line =~ "Int Value: (-?[0-9]*) .*" :: [[String]]); } in if matches == [] then "" else (last (head matches)); } in let { intStr = (getIntStr line); } in if intStr == "" then Nothing else Just (read intStr :: Word32)