Do such parsing tools exist for R? It does not have to be a lex / yacc compatible tool for my case.
(I'm an R newbie)
EDIT: I'm interested in implementing another language using R.
AFAIK, there is no parser generator for R.
However, user created packages in R (a.k.a. "extensions") can be written in Java, C or Fortran (and R, of course). So, you could use Lex/Yacc and Bison (in case of C) or JavaCC or ANTLR (for Java) to create a lexer and parser for your language and use those in your R code.