My thinking in this space has always started from a type inferred MetaLanguage but starting from a dynamic language does enable some interesting options. I tend not to touch dynamic languages, even going so far as to use transpilers, but I definitely would be more open to the idea of working with them if they had TypeScript level of gradual type checking and tool support. As you mention such a bidirectional transpiler would work I guess for things that don’t translate it could just give up and that’ll be part of the gradual typing aspect.

I would love to have TypeScripts type system on a Lua runtime, so I’ve been keeping an eye on Luau.

IMO a better approach is the one used by rescript and gleam. With a few careful restrictions of the target language you can fit it into a hindley-milner type system. These are extremely well understood, robust & usable, and give you a much smaller interface than the expansive turing complete one of TS.

I'm kind of surprised there's not an active project for a small ML language outputting lua code. I really wish gleam could pick it up as a third backend, it would be an amazing fit.

Roblox has a market cap near $100B and has multiple developers working full-time on Luau.

Luau is a backwards compatible superset of Lua that comes with it's own performance-tuned runtime. It offers more than just gradual typing.

So they are very different things. You can use Teal in cases when you don't control the runtime. Like write a Love2d game or your neovim config in it. Anywhere where Lua runs, you can use teal.

On the other hand Luau can offer superior developer experience because you don't have a separate compile step. They can do a lot more things that are impossible with teal as they have their own runtime and types do not get erased by compiling.