Hello all, I'm trying to traverse and process the algebra expression tree for a SPARQL query. For this purpose, I have created a class that implements OpVisitor and visits the entire tree in a top-down fashion. Ideally, I would like to be able to pass information from a visited operator to its children and vice versa, but I'm not sure how I can do this in an elegant way (using just some global class variables does not seem sufficient).
I guess a naive way to deal with it would be to start from the top of the tree, visit every Op, transform it to a custom extension of the respective Op that will maybe hold a link to the parent (already transformed) Op and store the information that will get passed to its children. At the same time, every such transformed Op will be inserted into a Stack and, after the top-down traversal is done, popped out in reverse order in order to go back up the tree and pass information from children Ops to parent Ops. Is there another more straightforward procedure to accomplish this? Sorry for sounding completely abstract, I hope I'm making (some) sense, any ideas/hints/pointers to examples would be very much appreciated! Dimitris
