module Main where

import Trace(trace)

fac :: Int-> Int
fac n     = fac0 n 1 where
  fac0 n acc = trace "Bah!" $
               if n == 0 then acc 
               else seq acc $ fac0 (n-1) (trace "Foo!" (n*acc))


getLines :: IO String
getLines = getit "" where
   getit res = do str<- getLine 
                  if null str then return res
                     else seq res $ getit (trace "Foo!" (res++ str))

main = 
  do putStrLn (show (fac 10))
     getLines >>= putStrLn