A few nice variations on Ruby’s yacc grammar have been emerging from the Grammarians. A few days ago, Xue Yong Zhi checked in his ruby.g, a parser in antlr syntax. Earlier this month, Sara di Gregorio and Pasquale De Medio contributed their simplified grammar to the antlr site, under Ruby’s own license. But these parsers just aren’t complete with some soul, in the form of the Ruby spec, which describes how Ruby internals act.
I’m not sure how we can get this stuff out to the CRuby team, but this is essential. The elephant shed in the room, as it were.