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 Intreqs :: [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_______________________________________________ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
