[1 of 1] Compiling Main             ( /in/foo.hs, /tmp/Main.o )

/in/foo.hs:3:16: error:
    * No instance for (Num String) arising from a use of `sum'
    * In the second argument of `($)', namely `sum li'
      In a stmt of a 'do' block: putStrLn $ sum li
      In the expression:
        do { li <- (map read . words) `fmap` getLine;
             putStrLn $ sum li }