Performs some special evaluation on the node.
This method has the responsibility for evaluating the children of the node
and it should generally call pv.eval(node.jjtGetChild(i)) for each child.
The SymbolTable is not passed as an argument. This is because
it is better practice to get and set variable values by using
node.GetVar().SetValue() rather that through the SymbolTable with
requires a hashtable lookup.
(in Jep.dll) Version: 188.8.131.52 (1.0.0)
the value after evaluation