src/Pure/Tools/print_operation.scala

clarified signature;

/*  Title:      Pure/Tools/print_operation.scala
    Author:     Makarius

Print operations as asynchronous query.
*/

package isabelle


object Print_Operation {
  def get(session: Session): List[(String, String)] =
    session.get_protocol_handler(classOf[Handler]) match {
      case Some(h) => h.get
      case _ => Nil
    }


  /* protocol handler */

  class Handler extends Session.Protocol_Handler {
    private val print_operations = Synchronized[List[(String, String)]](Nil)

    def get: List[(String, String)] = print_operations.value

    override def init(session: Session): Unit =
      session.protocol_command(Markup.PRINT_OPERATIONS)

    private def put(msg: Prover.Protocol_Output): Boolean = {
      val ops = {
        import XML.Decode._
        list(pair(string, string))(Symbol.decode_yxml(msg.text))
      }
      print_operations.change(_ => ops)
      true
    }

    override val functions: Session.Protocol_Functions =
      List(Markup.PRINT_OPERATIONS -> put)
  }
}