Array Index Out of Bounds Exception

I have a simple world (which is attached to this message) . Each time I click on the handle of the toggle, the world crashes. I think the problem lies in the 'Do Together' in the code that animates the carousel's horses. This is code that is similar to the carousel methods provided as delivered by Alice.

I'm wondering if anyone can download the world, confirm the crash and help me understand what I'm doing that is causing this. Thanks!

The full error message is:

Error during simulation.


Alice version: 2.0.7
os.name: Mac OS X
os.version: 10.4.10
os.arch: i386
java.vm.name: Java HotSpot(TM) Client VM
java.vm.version: 1.4.2-76
user.dir: /Applications/Alice.app/Contents/Required

Throwable that caused the error:
java.lang.ArrayIndexOutOfBoundsException: -1 not in range [0,2)
	at edu.cmu.cs.stage3.alice.core.Behavior$Fork.getNext(Behavior.java:113)
	at edu.cmu.cs.stage3.alice.core.Behavior$RuntimeStack.top(Behavior.java:55)
	at edu.cmu.cs.stage3.alice.core.Behavior.stackLookup(Behavior.java:269)
	at edu.cmu.cs.stage3.alice.core.Property.evaluateIfNecessary(Property.java:367)
	at edu.cmu.cs.stage3.alice.core.Property.getValue(Property.java:407)
	at edu.cmu.cs.stage3.alice.core.property.BooleanProperty.getValue(BooleanProperty.java:33)
	at edu.cmu.cs.stage3.alice.core.property.BooleanProperty.getBooleanValue(BooleanProperty.java:45)
	at edu.cmu.cs.stage3.alice.core.property.BooleanProperty.booleanValue(BooleanProperty.java:48)
	at edu.cmu.cs.stage3.alice.core.behavior.ConditionalBehavior.preSchedule(ConditionalBehavior.java:36)
	at edu.cmu.cs.stage3.alice.core.Sandbox.scheduleBehaviors(Sandbox.java:69)
	at edu.cmu.cs.stage3.alice.core.World.scheduleBehaviors(World.java:444)
	at edu.cmu.cs.stage3.alice.core.World.schedule(World.java:486)
	at edu.cmu.cs.stage3.alice.core.clock.DefaultClock.schedule(DefaultClock.java:94)
	at edu.cmu.cs.stage3.alice.authoringtool.AuthoringTool$11.run(AuthoringTool.java:689)
	at edu.cmu.cs.stage3.alice.authoringtool.util.DefaultScheduler.simulateOnce(DefaultScheduler.java:115)
	at edu.cmu.cs.stage3.alice.authoringtool.util.DefaultScheduler.run(DefaultScheduler.java:76)
	at edu.cmu.cs.stage3.scheduler.AbstractScheduler.run(AbstractScheduler.java:45)
	at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:189)
	at java.awt.EventQueue.dispatchEvent(EventQueue.java:478)
	at java.awt.EventDispatchThread.pumpOneEventForHierarchy(EventDispatchThread.java:234)
	at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:184)
	at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
	at java.awt.Dialog$1.run(Dialog.java:542)
	at java.awt.Dialog$3.run(Dialog.java:569)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.awt.Dialog.show(Dialog.java:567)
	at java.awt.Component.show(Component.java:1133)
	at java.awt.Component.setVisible(Component.java:1088)
	at edu.cmu.cs.stage3.swing.DialogManager.showModalDialog(DialogManager.java:58)
	at edu.cmu.cs.stage3.swing.DialogManager.showDialog(DialogManager.java:123)
	at edu.cmu.cs.stage3.alice.authoringtool.AuthoringTool.play(AuthoringTool.java:5087)
	at edu.cmu.cs.stage3.alice.authoringtool.Actions$15.actionPerformed(Actions.java:167)
	at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1819)
	at javax.swing.AbstractButton$ForwardActionEvents.actionPerformed(AbstractButton.java:1872)
	at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:420)
	at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:258)
	at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:247)
	at java.awt.AWTEventMulticaster.mouseReleased(AWTEventMulticaster.java:231)
	at java.awt.Component.processMouseEvent(Component.java:5166)
	at java.awt.Component.processEvent(Component.java:4963)
	at java.awt.Container.processEvent(Container.java:1613)
	at java.awt.Component.dispatchEventImpl(Component.java:3681)
	at java.awt.Container.dispatchEventImpl(Container.java:1671)
	at java.awt.Component.dispatchEvent(Component.java:3543)
	at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:3527)
	at java.awt.LightweightDispatcher.processMouseEvent(Container.java:3242)
	at java.awt.LightweightDispatcher.dispatchEvent(Container.java:3172)
	at java.awt.Container.dispatchEventImpl(Container.java:1657)
	at java.awt.Window.dispatchEventImpl(Window.java:1606)
	at java.awt.Component.dispatchEvent(Component.java:3543)
	at java.awt.EventQueue.dispatchEvent(EventQueue.java:480)
	at java.awt.EventDispatchThread.pumpOneEventForHierarchy(EventDispatchThread.java:234)
	at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:184)
	at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:178)
	at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:170)
	at java.awt.EventDispatchThread.run(EventDispatchThread.java:100)

The problem is flipping the lever, not the horse animation. That runs fine when you run that method by itself.

Attached is a version that works - I just elimated the "event while" and did the same thing with a world level method. This is a fairly unsatisfactory answer since I can see no real reason the original didn't work - and especially don't see why it would generate the error message it did. I only tried this because I'm suspicious of "event whiles" in general. (One problem with the original may have been the scope of the "flipped" variable as local to a method, however moving it to a world level variable didn't fix the problem.)