[rust-dev] Rust ANTLR grammar may be correct

The rust ANTLR grammar that lives at https://github.com/jbclements/rust-antlr/ appears to be largely correct, in the sense that it parses Rust source. There's a problem, in that the parser is currently SO DARN SLOW that I haven't been able to test it on the entirety of the rust repository yet. Parsing of TTs runs at about 2K lines per second, but the full program grammar starts at 200 lines/sec, then drops to 50, and finally may simply stall out completely. Fortunately, running fast is not the point. I've made a passing attempt to format the grammar to be readable and to conform to certain formatting conventions. I'd be grateful to anyone who has the time to make suggestions. NB, for those interested: our "restriction" mechanism, as expected, makes the rules for expression parsing much less pleasant; in particular, most of the expr hierarchy is duplicated at least once, and some of it is duplicated three times. Thanks for your time! John