The DEFEVENT command allows you to tie the operation of a Logo procedure to the occurrence of a particular event, including the activation of the Control-G key combination, or to operate on a scheduled regular basis. This allows you to handle the program user's attempt to break a program in the way you like or to cause your Logo procedures to operate or output on a regular basis without having to repeatedly call them.
There are two events defined which you can define. The BREAK event occurs every time the Control-G key is being pressed. Normally, a built-in event procedure will turn off the timer ticks (if a timer has been activated with the TIMER command) and return you to toplevel. You can modify this behavior by defining an event procedure for the BREAK event. Your definition should always provide the option of returning to toplevel. The TIMER event is activated with the TIMER command. This command starts a timer which, when elapsed, generates a TIMER event which can be used to activate a Logo procedure. Both the BREAK and the TIMER events do not generate any inputs for the event handling procedures.