A visitor mechanism for navigating and operating on a plan of
Operators. This class contains the logic to traverse the plan. It does not
visit individual nodes. That is left to implementing classes (such as
Guaranteed to always point to the walker currently being used.
Entry point for visiting the plan.
plan OperatorPlan this visitor will visit.
walker PlanWalker this visitor will use to traverse the plan.
Push the current walker onto the stack of saved walkers and begin using
the newly passed walker as the current walker.
walker new walker to set as the current walker.
Pop the next to previous walker off of the stack and set it as the current
walker. This will drop the reference to the current walker.
VisitorException if there are no more walkers on the stack. In
this case the current walker is not reset.