public class XEvaluatorVisitor
extends EvaluatorVisitor
implements Serializable

This class is used for the evaluation of an expression. It uses the Visitor design pattern to traverse the function tree and evaluate the expression using a stack.

Function nodes are evaluated by first evaluating all the children nodes, then applying the function class associated with the node. Variable and constant nodes are evaluated by pushing their value onto the stack.

Some changes implemented by rjm. Nov 03. Added hook to SpecialEvaluationI. Clears stack before evaluation. Simplifies error handling by making visit methods throw ParseException. Changed visit(ASTVarNode node) so messages not calculated every time.