I am still waiting for an LLM trained to focus on effin' regexes and their variants like sed, somebody please do a page with ads for this and you will have a nice little side income and warm fuzzy feeling on top of it.

Natural language -> fully working one, I don't mean some email validators but way more complex stuff. Although, I've recently had a case which was too much even for regexes in any form or spec, then sort of grammar-based parser needed to be done from scratch.