gistfile1.hs

-- 元はこれ https://github.com/haruyama/Haskell.Sample/blob/master/CommandLine/mygrep/Main.hs
-- ライセンス：https://github.com/haruyama/Haskell.Sample/blob/master/CommandLine/mygrep/LICENSE
import System.Environment
import System.IO
import System.Exit
import Control.Monad (filterM)
import qualified Data.Text as T
import qualified Data.Text.ICU.Regex as TIR
import qualified Data.Text.IO as TIO

-- getContents は一度に全部読み込んだりしないと聞いたので、私ならこう書くかな的な。
mainloop' :: TIR.Regex -> Handle -> IO ()
mainloop' reg inh = do
    c <- TIO.hGetContents inh
    matched <- filterM (matchesLine reg) $ T.lines c
    mapM_ TIO.putStrLn matched

main :: IO ()
main = do
    args <- getArgs
    if length args < 2
        then do
            hPutStrLn stderr "Usage: mygrep pattern file1 file2 ..."
            exitWith (ExitFailure 1)
        else do
            reg  <- TIR.regex [] (T.pack . head $ args)
            mapM_ (\fn -> withFile fn ReadMode (mainloop' reg)) $ drop 1 args
            exitSuccess

matchesLine:: TIR.Regex -> T.Text -> IO Bool
matchesLine reg line = do
    TIR.setText reg line
    TIR.find reg 0