You are essentially building a compiler from 4D to perl. In addition to the modules mentioned above, it is also possible to build your own top-down recursive descent parser. Each sub would represent a nonterminal and terminals generally correspond to regexes. Translation can either be done as you parse or by walking the parse tree afterwards.

I have hand-built parsers a number of times with good success. It allows one to really understand the nature of the language and customize as needed. Hand-built parsers can also be faster than P::RD, but this may not be a big consideration except in development of the compiler itself.

Whether you use the hand-built or module approach, I would recommend reading up on compilers to avoid pitfalls (such as ambiguous grammars) that would show up in either case. The best book I know of is "Compilers: Principles, Tools and Techniques' by Aho Sethi and Ullman.