I couldn't find anything (after a very superficial look) in the documentation for Regexp::Grammars about associativity. If the parser-generator doesn't support it directly, then you'll have to get associativity and precedence by rewriting the grammar. In Re: Left-associative binary operators in Parse::RecDescent, I give an overview of how to rewrite a grammar for operator precedence & associativity. It might suit your needs.