It’s worth noting that, thanks to grammarian Martin Traverso, the
latest version of ANTLR v3 can generate parsers in Ruby.
It’s still pre-alpha, but things only get better from here!
I believe there’s also a native Ruby port of ANTLR v2 bopping about
out there, though google isn’t helping me out much right now.
A decent LL parser generator really is worth it, though. LALR
Incidentally, it looks like Martin will be writing much of the ANTLR
v3 grammar for Ruby. He’s got quite a bit done in SVN already.