src/Pure/Tools/print_operation.scala

 
   class Handler extends Session.Protocol_Handler
   {
     private val print_operations = Synchronized[List[(String, String)]](Nil)
 
+    override def init(session: Session): Unit =
+      session.protocol_command(Markup.PRINT_OPERATIONS)
+
     def get: List[(String, String)] = print_operations.value
 
     private def put(msg: Prover.Protocol_Output): Boolean =
     {
       val ops =

       }
       print_operations.change(_ => ops)
       true
     }
 
-    override def init(session: Session): Unit =
-      session.protocol_command(Markup.PRINT_OPERATIONS)
-
     val functions = List(Markup.PRINT_OPERATIONS -> put _)
   }
 }