While I do think Teal is pretty cool, I think adding gradual typing by the having a static language that compiles down to a dynamic language Typescript-style is the worst way to add gradual typing support.
The extra compile step and the added complexity kind of kills the advantages of using a simple dynamic language like Lua in the first place. You can only compile a file if the types are correct. You might think this is good but no, not at at all. This is horrible for prototyping because sometimes you might want to test a specific path even when you haven't yet refactored the rest of the program.
It is much less hassle to just add type annotations as comments and have the linter figure it out. So you can have your cake and eat it too, having both type safety when you need and want it and the power and flexibility of dynamic typing in one.
Now, an even better way is probably what Luau is doing because you also have type information available at runtime which then can be used for reflection and performance. Especially as they have an option to disable the type checking if needed.
It’s kind of common to use the TypeScript compiler purely as a linter these days even in a TypeScript-only codebase. You actually want to use a faster transpiler anyway, and when you do, there’s no technical reason not to run the code or the test suite while you still figure out the types. In fact, I’m becoming convinced that this kind of setup (and way of working) is actually the best of both worlds.
Eh, I think I disagree with this. The point is that I can make very complicated libraries in Teal, and those compile down and are usable in lua scripts. This is where I actually used it - very simple scripts, very large and complicated library imported into those scripts. If you really need to prototype, just use lua, not teal. I've never found prototyping in teal to be a problem though.
On the other hand, I absolutely despise type annotations as comments. There is something so unclean about that - if I want a readable library, I want there to be type proofing all the way down. No switching between static and dynamic.
I don't think Teal can be total. Lua is super expressive and you would need to get deep into dependent types and whatnot to caption a fraction of the power of its types.
> Some Lua libraries use complex dynamic types that can't be easily represented in Teal. In those cases, using any and making explicit casts is our last resort.
Personally if I paid the cost of having an extra compile step then I would rather wish for some serious type safety like what Elm or Reason provide. But then you end up with a different language.
I agree though that for your use case of making complicated libraries Teal might be actually good fit.
I was going to argue that Luau is superior anyway if you really can't cope with annotations but obviously if you want to make libraries for lua users that doesn't work. (Though I guess you could technically compile down from Luau to Lua, just not sure if anyone has ever bothered.)
The extra compile step and the added complexity kind of kills the advantages of using a simple dynamic language like Lua in the first place. You can only compile a file if the types are correct. You might think this is good but no, not at at all. This is horrible for prototyping because sometimes you might want to test a specific path even when you haven't yet refactored the rest of the program.
It is much less hassle to just add type annotations as comments and have the linter figure it out. So you can have your cake and eat it too, having both type safety when you need and want it and the power and flexibility of dynamic typing in one.
Now, an even better way is probably what Luau is doing because you also have type information available at runtime which then can be used for reflection and performance. Especially as they have an option to disable the type checking if needed.