Update Parser.cup

This is the best first draft I can do.
I really hope it helps... :( It took me a while to make xD and I would probably cry if this is completely useless.
I can't test any of this so I will ask you to test it and debug it. I know it's horrible to work on someone else's code, so just tell me when you want to get together (if you want to) and I will tell you what I was trying to do with this and I can help you debug.