[Grammatica-users] Grammar for expression...?

[Morten Aune Lyrstad]

I have downloaded Grammatica for use with my scripting language 
Storyteller. I have serious problems understanding the more advanced 
grammar. I need to extend the expression grammar you have given in your 
example:

Expression = Term [ExpressionTail] ;

ExpressionTail = "+" Expression
             | "-" Expression ;

Term = Factor [TermTail] ;
   TermTail = "*" Term
       | "/" Term ;

Factor = Atom
     | "(" Expression ")" ;

Atom = NUMBER
   | IDENTIFIER ;


into one that is capable of handling all of a programming language's 
common operators, like 'and', 'or', > etc. However, I don't really 
understand what is going on here, and because of that I cannot extend 
it. Why are the operators divided into two "tails"? And does this 
support unary operators? Where should I add my other operators?

I was hoping you could give me a hand?

Thank you,
Morten