Hello, I am completely new to functional programming, am just reading through SOE (great book so far!) and try to understand streams in client-server-interactions. Therefore I wrote the following program (which has nothing to do with the book exercises), which is intended to read integers from stdin and to write the sum of the inputs so far to stdout. When I start it (in Hugs), I can enter numbers, but don't get back the sum, but every second time a zero, every forth time the value I just entered and every forth time the sum of the two values I entered the latest. Could s.o. explain me, what is going wrong? I can't figure out, what is happening here. (I know that there are easier solutions to the problem than using streams, but the latter was my intention for learning.) Thanks, Christian module Main where main = sequence reqs type Request = IO Int type Response = IO Int reqs :: [Request] reqs = client resps resps :: [Response] resps = server reqs client :: [Response] -> [Request] client (y:ys) = (do toPrint <- y putStr ("So far: " ++ show toPrint ++ "\nEnter number: ") line <- getLine return (parseToInt line)) : client ys server :: [Request] -> [Response] server = scanl helper (return 0) where helper :: IO Int -> IO Int -> IO Int helper sofar x = do a <- x sf <- sofar return (a + sf) parseToInt :: String -> Int parseToInt str = foldl nextDigit 0 (intList str) where intList :: String -> [Int] -- only for positive numbers so far intList = map (\x -> fromEnum x - 48) nextDigit :: Int -> Int -> Int nextDigit a b = a * 10 + b