-- Be Careful when running this file
-- spawned processes could hang up your system

import System.Process
import System.IO

tr input = do 
    let (cmd, args) = ("tr", ["a-z", "A-Z"])
    let process = (proc cmd args){ std_in = CreatePipe
                                 , std_out = CreatePipe
                                 , close_fds = True }
    (Just hin, Just hout, _, _) <- createProcess process
    -- inject data
    hPutStr hin input
    hClose hin
    -- return (IO String)
    hGetContents hout

tr' input = do
    let process = (proc "tr" ["a-z", "A-Z"]){ std_in = CreatePipe
                                            , std_out = CreatePipe 
                                            , close_fds = True }
    (Just hin, Just hout, _, _) <- createProcess process
    -- inject data
    hPutStr hin input
    hClose hin
    -- return (IO String)
    putStr =<< hGetContents hout
    hClose hout

test00 = mapM_ (\_ -> tr "Homebrew fork-bomb\n" >>= putStr) [0..50]
test01 = mapM_ (\_ -> tr' "Homebrew fork-bomb\n") [0..50]

main = test00 >> test01 >> wait
  where wait = do putStrLn "Press any key to quit"
                  input <- getLine
                  putStrLn (">>" ++ input)