Hi Dear Haskellers, I have this small program to grep recursively in parallel. It works fine, but generates the last line empty. Is this empty line coming from mapConcurrently()? Thanks, Hong -- mygrepr.hs -- lrf.pl is an old Perl script to get all non-duplicate files recursively under the current directory, since some of directories have tons of links -- the program runs concurrently on either specified number of threads or 3/4 of the number of available cores module Main (main) where import Control.Concurrent.Async import Control.Monad import Data.List import Data.List.Split import GHC.Conc import System.Environment ( getArgs ) import System.Exit import System.Process import Text.Regex.Posix main :: IO () main = do hs_argv <- getArgs if null hs_argv || any (=~ "-h") hs_argv || any (=~ "--h") hs_argv then putStrLn "mygrepr [+RTS -N[x] -RTS] [OPTION]... PATTERN" else do numCores <- getNumProcessors numCapas <- getNumCapabilities let numT | numCapas > 1 = numCapas | otherwise = max numCapas (numCores `div` 4 * 3) _ <- setNumCapabilities numT let numThreads = fromIntegral numT :: Double findResult <- readProcess "lrf.pl" [] [] let files = lines findResult let num_of_files = fromIntegral $ length files :: Double let chunks = chunksOf (ceiling (num_of_files/numThreads)) files results <- mapConcurrently (grep hs_argv) chunks let (_, grepResult, _) = unzip3 results putStr $ unlines $ nub $ filter (\line -> not (line =~ "Binary file .* matches")) $ lines (concat grepResult) grep :: [String] -> [String] -> IO (ExitCode, String, String) grep hs_argv files = readProcessWithExitCode "/tool/pandora64/.package/grep-2.5.4/bin/grep" (hs_argv ++ files) []