To avoid converting the grammar, maybe (untested) Parse::YAPP would work better. I've struggled with converting a grammer to Parse::RecDescent format before and I didn't like the process. I have not tried YAPP yet, but it appears to accept yacc-grammars more or less raw, which would be a good thing. Unfortunately, the documentation is not as good, and it appears less widely used. So, YMMV...