[shriramkmurthi]

Look at how we've structured the semantics of JavaScript, Python, etc. (E.g.: http://cs.brown.edu/~sk/Publications/Papers/Published/pclpk-..., http://cs.brown.edu/~sk/Publications/Papers/Published/pmmwpl..., http://cs.brown.edu/~sk/Publications/Papers/Published/gsk-es...). This is how you should go about creating a core of R, followed by an elaboration from the full language into the core. Steal an existing parser to get ASTs, then most of your time goes into desguaring.