Haskell Exception Handling

import IO
                
foo :: Int -> IO()    
foo n = do
 x <- try readLn
 case x of
     Left  ioerr -> if (n > 1) 
                     then putStrLn "Not a number!" >> foo(n-1) 
                     else putStrLn "Try too many times!"
     Right num   -> print (num + 12)
                            
main = foo 3