Hello, I was reading this block of code from http://jasani.org/2008/02/18/command-line-haskell-and-error-handling-example... main = do m <- hGetContents stdin nums <- mapM readM . lines $ m print (sum nums) `catch` (\e -> hPutStrLn stderr ("couldn't sum lines: " ++ show e)) readM :: (Monad m, Read a) => String -> m a readM s | [x] <- parse = return x | otherwise = fail $ "Failed to parse \"" ++ s ++ "\" as a number." where parse = [x | (x,_) <- reads s] I don't understand how line 5 works. I thought that the do notation there would be the same as: main = hGetContents stdin >>= \m -> mapM readM . lines $ m >>= \nums -> print (sum nums) >> `catch` (\e -> hPutStrLn stderr ("couldn't sum lines: " ++ show e)) But I don't understand how that makes any sense with that infix `catch`. It looks like catch doesn't even have a first argument. Please enlighten me. Thanks.