Come on, hand it to this author.
You must know that yacc is one of the glowing accomplishments of the computer age, and here is an excellent perl implementation. It even parses its own syntax (as such an application should).
Granted, the "documentation" is a bit scant, but between Calc.yp and YappParse.yp, and a couple of hours of quality hacking, you can get all the info you need.
Roll your sleeves up, tweak the _Lexer, write a couple of languages, and see your object code generated!
My hat's off to you, Francois.