src/Pure/System/tty_loop.scala

           else done = true
         }
         if (result.nonEmpty) {
           System.out.print(result.toString)
           System.out.flush()
-          result.clear
+          result.clear()
         }
         else {
           reader.close()
           finished = true
         }

     catch { case e: IOException => case Exn.Interrupt() => }
   }
 
   def join: Unit = { console_output.join; console_input.join }
 
-  def cancel: Unit = console_input.cancel
+  def cancel(): Unit = console_input.cancel()
 }