src/Pure/Tools/build.ML

 
     val res1 =
       theories |>
         (List.app (build_theories symbols last_timing Path.current)
           |> session_timing name verbose
-          |> Unsynchronized.setmp Output.protocol_message_fn protocol_message
+          |> Unsynchronized.setmp Private_Output.protocol_message_fn protocol_message
           |> Exn.capture);
     val res2 = Exn.capture Session.finish ();
     val _ = Par_Exn.release_all [res1, res2];
 
     val _ = Options.reset_default ();

             (Runtime.exn_message exn handle _ (*sic!*) =>
               "Exception raised, but failed to print details!");
     in Output.protocol_message (Markup.build_theories_result id) [result] end);
 
 end;
-
-structure Output: OUTPUT = Output;  (*seal system channels!*)