This method is called after all of the children of
have been visited. In this case, these children were visited by the
. This is the last chance for the visitor to
modify the tree rooted at
. This method will be called
exactly the same number of times as
That is, for each node that is not overridden,
are each called exactly once.
Note that if
old == n then the visitor should make a copy
n before modifying it. It should then return the
This method is typically called by the method
leave(parent, old, n v).
If a subclass overrides the method
leave(parent, old, n v)
then this method may not be called.