Let's assume I have the production:
Expression // These are my semantic actions
: Expression PLUS_TOKEN Expression ( create_node(Expression, Expression) )
| SimpleExpression ( SimpleExpression ) (* Returns a node of type expression *)
Notice how I can't tell which Expression is which in my top most production's semantic action. How do I refer to the left and right Expression? What if I have three or more 'Expression's appear in the same production?