Need Help! Play/Pause Button

I need help in writing a code for a switch object similar to the play/pause function. I know the event handler for it would be if the mouse is clicked on the certain object do "this". I know how to make it turn forward 1/2 revolutions when the handle is clicked. But my problem is I want it to turn 1/2 revolutions backwards if I click it again. I'm having a hard time on this matter. Can someone please help! I'm new to alice and I really need help on this matter. Thank you.