introduce some helper methods

lib/risc/position/code_listener.rb

@@ -48,7 +48,7 @@ module Risc
         Position.set_to(position , at)
         if code.next
           listener = PositionListener.new(code.next)
-          position.register_event(:position_changed , listener)
+          position.position_listener( listener)
         end
         at += code.padded_length unless at < 0
         code = code.next

lib/risc/position/instruction_listener.rb

@@ -62,7 +62,7 @@ module Risc
         nekst = instruction.next
         if nekst
           listener = InstructionListener.new( nekst , code )
-          position.register_event(:position_changed , listener)
+          position.position_listener(listener)
         end
         instruction = nekst
       end

lib/risc/position/position.rb

@@ -34,6 +34,20 @@ module Risc
       Position.set_to(self , pos)
     end
 
+    # utility to register events of type :position_changed
+    # can give an object and a PositionListener will be created for it
+    def position_listener(listener)
+      unless listener.class.name.include?("Listener")
+        listener = PositionListener.new(listener)
+      end
+      register_event(:position_changed , listener)
+    end
+
+    # utility to get all registered listeners to the :position_changed event
+    # returns an array
+    def position_listeners
+      event_table[:position_changed]
+    end
     #look for InstructionListener and return its code if found
     def get_code
       listener = event_table.find{|one| one.class == InstructionListener}