gistfile1.rbx

      def create_listener(superclass, methodname, &block)
        focus_listener_class = Class.new() do
          include superclass
          implement superclass
          def initialize(methodname, &block)
            self.class.instance_eval do # <-- instance_eval makes this possible. :)
              define_method(methodname, &block)
            end
          end
        end
        
        focus_listener_class.new(methodname, &block)
      end