Lua + ellipses

[langston-barrett]

As a general principle, the Lua API should subsume all other features:

• bind and meta subsume normal metavariables
• ${{true}} subsumes $_
• match and rec subsume sub-patterns
• rx and negation replace explicit/special support for these features

However, Lua can't replace $... What would such an API look like? Perhaps ${{lua}}.., where lua would have access to a sequence of nodes' text ts and a sequence of kinds ks? An even more general API would be something like ${{cond||lua}}.. that functions like a take-while, where cond is repeatedly evaluated (in the same context, so it can use state) and siblings are repeatedly consumed until it returns false, and then the lua code gets executed with all the consumed siblings.

[langston-barrett]

Yet another alternative would be to expose a notion of "focus" or "current node" to the Lua code, which it could manipulate (get and set) freely. This, combined with an optionality construct (perhaps ${{lua}}?) would be enough to implement take-while or ellipses. Indeed, it would be more general. This would require #4.