src/Pure/System/isabelle_process.ML

             else (Runtime.exn_system_message exn handle crash => recover crash);
       in protocol_loop () end;
 
     fun protocol () =
      (Session.init_protocol_handlers ();
-      Output.protocol_message (Markup.ml_pid (ML_PID.get ())) [];
+      Output.protocol_message (Markup.ml_pid (ML_Pid.get ())) [];
       message Markup.initN [] [XML.Text (Session.welcome ())];
       protocol_loop ());
 
     val result = Exn.capture (message_context protocol) ();