I gave up on Menhir after I understood how allocation-heavy it is during the hot path, at least in the incremental API which is needed for proper errors; and how much of a giant hack you need to force extra lookahead, which shouldn't be such a big deal for parser generators.

These days I just handroll recursive descent parsers with a mutable stream record, `raise_notrace` and maybe some combinators inspired by FParsec for choices, repetition and error messages. I know it's not as rigorous, but at least it's regular code without unexpected limitations.

Could be, I'm not that far along yet. I've only just peeked into the incremental API. I'm still using the error token to try to improve my messages. It's just for syntax errors anyway, right?