src/Tools/Graphview/src/mutator_event.scala

 */
 
 package isabelle.graphview
 
 
+import isabelle._
+
+import scala.collection.mutable
+
 import java.awt.Color
 
 
 object Mutator_Event
 {
   type Mutator_Markup = (Boolean, Color, Mutator)
-  
+
   sealed abstract class Message
   case class Add(m: Mutator_Markup) extends Message
   case class NewList(m: List[Mutator_Markup]) extends Message
+
+  type Receiver = PartialFunction[Message, Unit]
+
+  class Bus
+  {
+    private val receivers = new mutable.ListBuffer[Receiver]
+
+    def += (r: Receiver) { Swing_Thread.require(); receivers += r }
+    def -= (r: Receiver) { Swing_Thread.require(); receivers -= r }
+    def event(x: Message) { Swing_Thread.require(); receivers.foreach(r => r(x)) }
+  }
 }