There was a really cool parsing paper at POPL this year [1] that goes 'beyond CFGs'... but as far as I know their system YAKKER is still in development / unrele

There was a really cool parsing paper at POPL this year [1] that goes 'beyond CFGs'... but as far as I know their system YAKKER is still in development / unreleased. I think from a user's perspective, e.g. someone wanting to design a DSL, it would be nice to be able to write down arbitrary CFGs and not necessarily have to know lots of technical parsing details ("what are all these shift-reduce conflicts!?"). Maybe PEGs aren't the best choice for this (no left recursion)-- MetaBorg's SGLR is probably state-of-the-art then like Zef said. Though one of the nice things about PEGs is no ambiguity; MetaBorg will do type-based disambiguation but only after parsing finishes. I'm working on an undergraduate thesis on 'extensible syntax' right now, trying to jump off from some of their stuff (but using a variation on Earley parsing) in particular to see if we could use types to help disambiguate incrementally during parsing. [1] http://portal.acm.org/citation.cfm?id=1706347 http://portal.acm.org/citation.cfm?id=1706347