callProgram :: FilePath -> [String] -> Maybe FilePath -> IO Bool
callProgram prog args cwd = do
  h <- runProcess prog args cwd Nothing Nothing Nothing Nothing 
  e <- waitForProcess h
  return $ e == ExitSuccess 
callProgram :: FilePath -> [String] -> Maybe FilePath -> IO Bool
callProgram prog args cwd = do
  h <- runProcess prog args cwd Nothing Nothing Nothing Nothing 
  e <- waitForProcess h
  return $ e == ExitSuccess 
callProgram prog args cwd = do
  h <- runProcess prog args cwd Nothing Nothing Nothing Nothing 
  e <- waitForProcess h
  return $ e == ExitSuccess 