This will parse the productions for a given file node
if a rule editor is open for the file it just forwards the call to the
open rule editor, else it opens the file and attempts to parse the
productions
This class follows the visitor pattern
it is based on Object-Oriented Design patterns in C++, later converted to Java
We might want to visit a traversal in Pre, Post, or In Order a PrePostVistor
allows this operation by letting a derived class support that operation