Teal is like typescript for Lua:
>>> Every type in Teal accepts nil as a valid value, even if, like in Lua, attempting to use it with some operations would cause a runtime error, so be aware!
I know you can use (or implement your own in about 8 lines) strict.lua[2], but that just seems like such a shame to omit nil checks from a gradual type system. I still follow the project, but I put a little more hope in Pallene's[3] development, although the aims are slightly different.
[1]: https://github.com/teal-language/tl/blob/master/docs/tutoria...