How confident are you in the soundness of the type system?
Also, are there any Lua constructs that are difficult/impossible to type?
Is type checking decidable? (Is the type system Turing complete?)
replies(3):
Also, are there any Lua constructs that are difficult/impossible to type?
Is type checking decidable? (Is the type system Turing complete?)
* Your type system cannot be sound. It's going to have escape hatches and exceptions because that's how dynamic languages roll.
* There will always be constructs that you can't type. See above.
* If your type system is going to usefully type enough of the ecosystem, it will be Turing complete.
All of these things are the trade-offs you make when you set out to layer types on a dynamic language, and they're well worth it to get 99% of the way to type safety in a language that otherwise couldn't scale. Theoretical purity is meaningless if the language isn't useful.
This one I disagree with. Type assertions with runtime checks could keep the typed fragments sound, unlike TypeScript and Python. Also see Elixir's strong arrow proposal for how to encode which assertions can be elided on function calls (because the function will assert them already).
You might be interested in checking out Pallene. Like Teal it's also Lua with types but it does check types at run-time, in an efficient way. However, Pallene's type system is currently not as featureful and production ready as Teal.