So Teal is to Lua as TypeScript is to JavaScript. Which means it automatically plays well with any Lua environment. Unlike luau and nelua which are also statically typed but have their own runtimes.
What version of Lua does it use? Lua gets new versions every few years so I don't know why so many impls don't continuously upgrade to the latest version.
Genius design.
It's got an awesome C API. It's fast, lightweight, and embeddable. It's more performant than Python. It's a staple in video game scripting.
Semantically, Lua is almost identical to the core of JavaScript. Metatables are a genius alternative to prototype chains.
Lua's syntax is beautifully simple and unambiguous, but at the cost of being moderately inconvenient in 2025 unfortunately. It could benefit from an ESNext-style renewal.
I get why they made the C API that way, but in practice it's very easy to get wrong.
I'm not sure how fast vanilla Lua is today compared to similar languages. I think LuaJIT (and Luau?) are most often used when performance is needed.
Like another commenter said, using . instead of : is maybe the most common mistake, too easy to make. And Lua offers no help preventing or checking it.
TypeScript is a great language. So is Lua. So is C.
When used carefully to avoid their warts. Learning how to do that for any language takes time and practice though.
Yea, and then there's javascript (or typescript if you prefer), the C++ of scripting languages. It's sometimes difficult to see any value through the warts. (Unless you're paid to, of course.)
yuescript, from the dora-ssr game engine dev, is essentially moonscript-2.0
And of course, if you want to treat lua as the scheme-like it really is (deep down), then ... fennel.
Lots of choices. They all compile to straightforward lua, are very easy to incorporate (you can even compile at runtime, if you wish), and all employ full lua semantics, meaning zero runtime overhead
EDIT: and the curse of not reading fully ahead strikes again (doh!). Someone else has made the same points below ...
LuaJIT is famously on 5.1 with no signs of moving.
And the extension is .tl
Generally colors are named after things in nature and not the other way around, given that the latter would’be had names for a long time, and most color names are comparatively recent inventions, driven by modern dyes and pigments and status, fashion, etc concerns. A West European peasant in the 11th century would’ve known the bird well, possibly trapped them for food, but would’ve had very little need for a separate word for ”blue-green”.
The history of color words is quite interesting. There’s a specific progression that almost all languages have gone through. It’s fairly well known that many East Asian languages don’t have separate names for ”blue” and ”green” at all (except as modern loans). Accordingly, they don’t usually make the distinction mentally, one could think that they simply consider them hues of ”cyan”.
Arrays: {number}
How does it disambiguate it? Are single-element tuples just never used in practice? To be fair, maybe the only time I've had to use them in TypeScript is via Parameters<T>
LuaJITted Lua code runs at 80% (on average, sometimes faster!) of the compiled C version of the same algorithm, typically. Lua is embedded in a surprisingly massive number of products: https://en.wikipedia.org/wiki/List_of_applications_using_Lua The startup time of a script is in nanoseconds. An "echo" written in Lua runs faster than the native echo implementation.
The only warts so far are 1-based indexing (you get used to it), and the fact that LuaJIT is stuck at Lua 5.1 while Lua itself is up to 5.3 or 5.4 and has added some niceties... with Lua proper running slower. And no real standard library to speak of (although some would argue that's a feature; there are a few options and different flavors out there if that's what you need, though- Such as functional-flavored ones...)
Anyway, there's nothing else like it out there. Especially with its relative simplicity.
There are also some neat languages that compile to (transpile to?) Lua, and deserve more attention, such as YueScript https://yuescript.org/, which is a still actively-updated enhanced dialect of MoonScript https://moonscript.org/ (described as "Coffeescript for Lua", although it hasn't been updated in 10 years) although neither of these are typed. HOWEVER... there IS this: TypescriptToLua https://typescripttolua.github.io/, which takes advantage of ALL the existing TypeScript tooling, it just outputs Lua instead of JS!
Lack of LuaJIT for 5.1+ isn't that big of a deal for desktop apps. The embedded world is still stuck in 5.1, but for them, the benefits of the latest Lua is marginal.
I was expecting Teal to be "Lua + type annotations", similar to Mypy. However from a quick look it does indeed seem to be a "dialect" in its own right. Teal is Lua-like and compiles to Lua, but there's more to it than just static types. Perhaps it's more similar to TypeScript?
For example, Teal replaces Lua's tables - the language's signature single, highly-flexible data structure - with separate arrays, tuples, maps, records and interfaces. It changes the variable scoping rules and even adds macro expressions.
Teal therefore seems substantially more complex than Lua. The author recognizes this in the conclusion to a recent presentation [0]: Lua is "small and simple", maybe Teal is "something else"? Lua is for "scripting", maybe Teal is better suited to "applications/libraries"?
https://github.com/Benjamin-Dobell/IntelliJ-Luanalysis
Admittedly, I've been focused on some other things recently, but still with some focus on type safety e.g. https://breaka.club/blog/godots-most-powerful-scripting-lang...
Funny you should mention that:
> It aims to fill a niche similar to that of TypeScript in the JavaScript world, but adhering to Lua's spirit of minimalism, portability and embeddability.
They're all just Lua tables with specialized type checking for specific behavior.
I really wish the Lua authors would add official types to Lua. The time has come.
Never going to happen IMO. Adding static types would change the nature of the language completely, even more than it has in Python.
As Teal shows, it would require giving up one of Lua's core features: tables as the language's single data structure. It would significantly complicate a language known for its simplicity.
Even the implementation would need to change radically - adding a type checker would invalidate the current approach of using a single-pass source-to-bytecode compiler.
> Never going to happen IMO. Adding static types would change the nature of the language completely, even more than it has in Python.
You both are kind of right.
The Lua authors have been working on the new companion language to Lua named Pallene. Pallene is a subset of Lua that adds types, not for the sake of types themselves, but for the purpose of performance. The Pallene compiler can generate optimized native code that potentially removes the need to manually write a module for Lua in C.
The other cool trick is that Pallene and Lua are completely interoperable with each other, so Pallene can be added to existing Lua projects, and you can opt to use regular Lua for the dynamic parts of your code where compilers won't be able to optimize much and strong types might be more trouble than help.
Here is a talk Roberto Ierusalimschy gave about Pallene. https://www.youtube.com/watch?v=pGF2UFG7n6Y
Mypy is just one type checker for Python, but there are many others including pyright. In fact pyright is quickly becoming the dominant checker over mypy.
IIRC Mypy started off as a type annotation syntax and corresponding type checker for Python. Mypy's type annotations were adopted by Python itself (in version 3.5 - PEP 484), which reduced Mypy's role to be just a type checker.
Since then, type annotations have indeed become a core part of Python - not only are they used in frameworks and libraries, but are also required to use language features like @dataclass.
https://peps.python.org/pep-3107/
MyPy was one such tool, and I think it had conventions for adding type annotations in comments, in places where Python didn't yet support them (such as variable assignment), but I'm pretty sure it was never a TypeScript-style pre-processor - type-annotated programs always ran directly in the unmodified CPython interpreter.
By ambitiously adding useful features, could Teal push the upstream to make progress? Probably not because Lua's scope is intended to be small (and we're no longer in the same context as 2015 era Typescript and tc39), but it's interesting to think about.
It is gradually typed, so no need to use Teal.
Also, are there any Lua constructs that are difficult/impossible to type?
Is type checking decidable? (Is the type system Turing complete?)
Teal's types are hints, like Python's and TypeScript's, so I suspect it's not sound by design.
> Also, are there any Lua constructs that are difficult/impossible to type?
Teal includes several types that model typical uses of Lua tables, e.g. as arrays, maps etc. It doesn't look like it can type fully general use of Lua tables, e.g. using both the "array part" and "hash part" of the same table.
* 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.
A couple things I want from teal: 1. I wish there was a better way to bundle files together. I have a little build.lua, but eh, I think it could be better. I know of cyan and everything but I feel like that was developed for a different application than mine. I want to have 1 complete file that I can just give people and allow them to do synbio work in any target language with a lua machine. 2. There are some annoyances around luajit vs lua5.1 functionality 3. The compiler yelling at you gets old for integrating raw lua. I tried to port json.lua in and even with the definition file, I couldn't embed the whole json.lua without having compiler errors. So eventually I just imported it as a string that is type checked, which is bad 4. I really wish syntax highlighting on github was a thing
The good bits:
It's pretty much complete. I used it a couple years ago and there were things with generics that I just couldn't do, but now it is much better. For example, how I use generics for the different parsers (fastq, fasta, genbank, slow5, pileup, etc) https://github.com/Koeng101/libB/blob/dev/src/dnadesign/src/...
Overall, love it! It is one of those pieces of software which is nearly complete, and I love using software like that.
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