main :: IO ()
main = do
    putStrLn "Enter numbers: "
    putStrLn "These will be summed until zero is entered."
    sum <- sumInts
    print sum

get_Int :: IO int
get_Int = do
          a <- getLine
          return (read a :: Int)

sumInts :: IO int
sumInts = do
          num <- get_Int
          if num == 0
             then return 0
             else (do sum <- sumInts
                      return (num+sum))