Help with SemanticParser

I have been trying to create my own JavaScript implementation based on the Simple Language AddOn. The reason I am not using the Dynamic JS implementation that comes with the product is that I want to have the "red wavy lines" show up for bad syntax.

That said, I am having some trouble wrapping my head around the complexity of creating a Semantic language using the Grammar.xml.

My problem right now is that I am trying to allow simple function calls. For example: I am trying to modify the NonTerminal "Statement" to support these function calls. What I thought I would do add a "FunctionAccessExpression" to "Statement". But since the Assignment statement already contains a reference to "Expression" the XML won't compile.

Can you guide me down the proper path for doing something like this?

Thanks!
Gil