GUISwarm is a subclass of Swarm that is used as a toplevel Swarm for simulations running with a graphical user interface. The GUISwarm creates a ControlPanel automatically for you and defines a -go method that interprets the state of the ControlPanel to keep things running in response to user input. Users subclass GUISwarm much like they subclass a normal Swarm, implementing the same kind of buildObjects, buildActions, and activateIn methods. When you are done building your Observer Swarm, start it as a toplevel via [myGUISwarm go].
The control panel places a few responsibilities on the GUISwarm subclass author. In particular, a message to [controlPanel doTkEvents] should be scheduled fairly frequently - only when that method is executed will the user interface update (and the stop button be checked). Also, it is often useful to use [controlPanel setStateStopped] to wait for the user to indicate they're ready for execution to proceed.