There is no use for breaking a function. It always returns to its call.
A loop you can break with System > (General) Stop Loop. Keep in mind that all actions and events after the 'stop loop' will continue to run, the 'stop loop' just prevents the loop from running again from its top-event.
I know that a fucntion always returns to its call position, but I want to return earlier if a certain point has been reached in the function.
It's hard to explain, but I have a function creating a path randomly. Sometime it reaches the edge before the function has been completed, so I want to return then to the caller, so that the rest of the function will not be executed.