-- this is an interactive program to read in two numbers and print their sum.
 
 module Main where
 
 main = readChan stdin abort $ \userInput -> 
        let inputLines = lines userInput in
         readInt "Enter first number: " inputLines $ \num1 inputLines1 ->
         readInt "Enter second number: " inputLines1 $ \ num2 _ ->
         appendChan stdout ("Their sum is: " ++ show (num1 + num2)) abort done
 
 readInt :: String -> [String] -> (Integer -> [String] -> Dialogue) -> Dialogue
 
 readInt prompt inputLines succ =
   appendChan stdout prompt abort $
   case inputLines of
      (l1 : rest) -> case (reads l1) of
                        [(x,"")] -> succ x rest
                        _        -> appendChan stdout
 	                              "Error - retype the number\n" abort $
 	                           readInt prompt rest succ
      _          -> appendChan stdout "Early EOF" abort done