Years ago, I tried lua and wasn't impressed. Then I started using Neovim, did the necessary configuration in lua, but continued writing my own scripts in vimscript. Later I started using wezterm and decided to give lua a second shot, and I began to really like it.
I realized my initial dislike for lua stemmed from my experience with javascript (back in the jwquery days), where maintaining large codebases felt like navigating a minefield. The lack of type system made it all too easy to introduce bugs.
But lua isn't like that.
It's not weakly typed like javascript - it's more akin to pythons dynamic duck typing system. Its simplicity makes it remarkably easy to write clean maintainable code.
Type checking with type is straightforward compared to python, mostly because there are only five basic types (technically seven but I've never used userdata or thread).
And I even started to enjoy using metatables once I understood how and when to apply them.
That being said, lua's lack of popularity probably stems from its limited stdlib, which often feels incomplete, and the absence of a robust package manager.
luarocks is a pain to work with.
All that being said, I don't really see the point of using this project.
While I do wish type annotations were a native feature, the ones provided by the lsp are good enough for me.
pmarreck · 12h ago
I've been diving into Lua (a little late to this party, but turns out it's a perfect language to rewrite some commandline scripts I had that were getting unwieldy in Bash, especially with LLM assistance!) and it's really something of an eye-opener.
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!
Rochus · 1h ago
> LuaJITted Lua code runs at 80% (on average, sometimes faster!) of the compiled C version of the same algorithm, typically
Cannot confirm this. It might be true on selected micro benchmarks. Here are the results of the Are-we-fast-yet benchmark suite, which includes a decent set of benchmarks challenging CPU, cache and memory access: https://github.com/rochus-keller/Oberon/blob/master/testcase....
On average, the C and C++ implementations are five times faster than LuaJIT.
Symmetry · 1h ago
The code in Are-we-fast-yet has been heavily optimized. It might still be true that naive LuaJIT can run almost as fast as Naive C.
Rochus · 22m ago
Have a look at the results; there are benchmarks in the suite where C/C++ is "only" twice as fast as the corresponding (idiomatic) Lua implementation, but on average (geomean of all factors) it's about five times as fast.
kanbankaren · 12h ago
It is true that LuaJIT is stuck at 5.1, but you could write any performance critical sections in C/C++ and call it from Lua.
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.
johnisgood · 2h ago
And despite it being stuck at 5.1, it still implements features from other versions. For example, there is the "LJ_52" macro, so you can compile "table.pack" and "table.unpack" into LuaJIT, which I do, because I use both at times.
There is also the compat53 library which polyfills most of the missing parts. The Teal compiler has --gen-target and --gen-compat flags which adapts the generated Lua code for different Lua versions, and allows using the compat53 library behind the scenes if desired, so you can get a mostly Lua-5.3+ experience over LuaJIT using Teal.
vrighter · 6h ago
and if you use luajit ffi, those calls actually get called just as fast as from a c program
jiehong · 2h ago
Any recommendations going from bash to lua to watch out for except indexing?
pmarreck · 49m ago
I haven’t found many downsides yet. I was already starting to rewrite some things in Awk (which I was drawn to for similar reasons- fast script startup time, simple easy language with good defaults), but Awk (while still also awesome) isn’t really designed for stuff beyond a certain size (no signal handling unless you use a fork, for example)
LuaJIT is missing bignums, ints that aren’t floats, bit operations, and native utf8 handling, but it can pretty easily be extended with libraries, ffi and metatabling. (I actually made a working bignum library that integrates with gmp, but it has a memory leak somewhere and it’s a rabbit hole/bikeshedding project at this point…)
LLM assistance helps hugely and I really like YueScript’s syntax additions. You can point any LLM at a syntax describing webpage and it will pretty much write that language for you…
pansa2 · 12h ago
> Teal is a statically-typed dialect of Lua.
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"?
It's interesting that you mention Typescript. In Typescript's early history, they added a bunch of features that they either thought would make it nicer for C# devs (classes, enums, option chaining, decorators, namespaces, etc.). Eventually, a bunch of these features were added to Javascript natively in nearly the exact same way they were implemented in Typescript. Now, the only remaining non-type-related features not added to Javascript are enums and namespaces, which will never be added because they're poorly designed. Even the Typescript type syntax (but with ignored semantics) may get added to Javascript under a WIP proposal. Some of these features were perhaps mistakes -- private in TS and private in JS will never be able to mean the same thing, and `class` syntax is iffy -- but overall there was an improvement.
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.
koito17 · 7h ago
Minor nitpick: decorators are still in "stage 3". Not formally part of ECMAScript standard yet.[1]
Anyway, that has not stopped large parts of the JavaScript ecosystem -- notably Angular -- from using an experimental variant of decorators, such as the one provided by TypeScript. [2]
Enums are possibly going to end up in JS eventually - this proposal[0] is at stage 1 (i know the readme says stage 0, it looks like there is a PR to update this). Granted, that means 'under consideration' but it is a start
Teal still compiles all those things into plain Lua tables, it's just that the type system has different table subtypes for better type checking. I think the variable scoping is also the same as regular Lua?
lifthrasiir · 11h ago
That was a major concern when I was using Lua at work. Pretty much every type checker in Lua required transpiling, which doesn't work for many environments (e.g. Redis script). My Kailua [1] was designed that in mind but didn't reach its full potential.
Just a small note about mypy and python - annotations are first-class citizens in Python3 and are not tied to any particular type checking system such as mypy, but are instead a core part of the language and actually serve vital functions in frameworks and libraries that are used to check interfaces such as Pydantic and FastAPI (eg URL params).
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.
pansa2 · 11h ago
Am I right in thinking that Python's type annotation syntax originally came from Mypy though?
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.
thristian · 10h ago
No, Python's current type annotation syntax was added in Python 3.0 as a generic annotation syntax, in the hope that somebody else might come along and build a type-checker or other tooling on top:
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.
90s_dev · 11h ago
> Teal replaces Lua's tables - the language's signature single, highly-flexible data structure - with separate arrays, tuples, maps, records and interfaces
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.
pansa2 · 10h ago
> I really wish the Lua authors would add official types to Lua.
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.
dottrap · 9h ago
>> I really wish the Lua authors would add official types to Lua.
> 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.
Disappointed that it maintains syntactic Lua compatibility. Would have been a good time for a clean slate on the shoulders of hindsight.
lifthrasiir · 7h ago
In reality, tables are used in specific fashions and not fully generally. (Partly because Lua itself even recognizes some of these fashions and provides relevant operations accordingly.) Lua tables are not really a single data structure; it is a single type that acts as multiple data structures at once.
90s_dev · 59m ago
Yeah Lua optimizes array tables for performance as long as they're arrays. That's the only optimization I'm aware of. I get why they didn't just add arrays, to keep the syntax and semantics clean, simple, and unambiguous. I just don't like it. If you take that to its extreme, you get Lisp. Natural human languages are messy and full of warts, but they work despite that, or perhaps because of that, because human life is messy and warty. "Pure" languages never can or do catch on. My favorite language right now is unironically TypeScript despite all its baggage.
tiffanyh · 1h ago
> As Teal shows, [official typed Lua] would require giving up one of Lua's core features: tables as the language's single data structure.
Is that true ... you can't have typed tables without giving up tables as a data structure?
krapp · 1h ago
You can't have typed tables without giving up tables as the language's single data structure. You would have tables and typed tables which are essentially just arrays with extra steps.
90s_dev · 1h ago
Not with type erasure like TypeScript does. Then it would just be type checking hints as to how the table is used, not a different kind of table. Teal does this.
wyldfire · 11h ago
> Perhaps it's more similar to TypeScript?
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.
Benjamin_Dobell · 12h ago
You can get pretty far by bolting annotations onto Lua (no compilation step), for example using my IDE:
I'm so relieved to see more types being added to good languages.
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.
hisham_hm · 42m ago
Teal currenly supports generating code for Lua 5.1 and up, including LuaJIT. There are compiler flags --gen-target and --gen-compat which control various specifics of code generation.
RS-232 · 12h ago
Lua is a good language. It's like C, if C were a scripting language.
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.
90s_dev · 12h ago
It's nothing like C, and that's so much of its charm.
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.
growlNark · 12h ago
Sure, if you compare via semantics Lua and Javascript make sense to liken. But in terms of complexity, Lua is far more like C. There's no unfucking all the horrible decisions baked into javascript and I wouldn't touch it with a ninety-foot pole, but Lua still has some hope.
SkiFire13 · 1h ago
To be fair Lua also made some bad decisions, though maybe not as bad as javascript:
- tables being used for both objects and arrays can create a lot of confusion, especially when you have some integer keys, but not all, and especially when they are not consecutive or one of them is 0
- indexes start at 1
- assigning nil deinitializes variables/entries instead of assigning the value `nil` (this becomes especially bad if you mistakingly try to use nil as a value in an array/table)
- nil and false are falsy, but not 0, which instead is truthy
90s_dev · 12h ago
Every language has warts. Even Lua.
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.
growlNark · 12h ago
> Every language has warts.
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.)
90s_dev · 11h ago
Every time someone says this about JavaScript, their favorite language turns out to be something like APL or Ada.
growlNark · 12m ago
Having a favorite language is weird (to me). They're tools, and some are more effective and usable than others, and some are better suited to some tasks than others.
But, equivalently, of course I'm going to criticize a hammer if it's literally covered in warts making it difficult to grasp without slipping. (or, if the gun I'm trying to use keeps firing bullets into my foot when I'm aiming down range.)
isr · 11h ago
FYI, for those who may not be aware, moonscript is the "coffeescript" for lua. It has been in production use for quite a while (the author of moonscript also created itch.io, using ... moonscript).
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 ...
3036e4 · 7h ago
If Teal is the TypeScript of Lua, Fennel is the ClojureScript. Except Fennel is fully implemented in Lua itself and it transpiles (usually) to very simple, plain Lua code without much (if any) overhead and with no run-time library other than what is in Lua itself.
I don't think it's a good language, and I hate it. I've made thousands of the same mistakes with it—typing . instead of :. There's a reason Lua has a smaller audience than assembly.
Philpax · 4h ago
> There's a reason Lua has a smaller audience than assembly.
I don't think that's true. It's a very embedded language. Its use in video games and video game modding alone would outnumber the number of people directly writing assembly to achieve things.
90s_dev · 1h ago
It's also a very old embeddable language, which is probably most of why it's so often chosen for that purpose. Many similar languages have been written from scratch inspired by Lua over the last 10-15 years, some of them almost definitely better than Lua in many respects, but they get no traction because Lua has all the steam. Unfortunate, because the authors of Lua are fairly happy with semantic and syntactic decisions that many of us are very unhappy with.
shakna · 3h ago
Or the number of routers that are using it, or other deployable hardware...
0cf8612b2e1e · 11h ago
Each new Lua version has breaking changes that are of dubious value to keep on the upgrade treadmill. Something like a Python2->3.
LuaJIT is famously on 5.1 with no signs of moving.
bondant · 6h ago
Not moving straight to a more recent version, but still cherry-picking some parts of them. You can see some functionalities from Lua 5.2 and 5.3 are working in Luajit: https://luajit.org/extensions.html
90s_dev · 1h ago
I guess all of this means Lua has "flavors" more than "versions".
90s_dev · 13h ago
> The core compiler has no dependencies and is implemented as a single tl.lua file which you can load into your projects. Running tl.loader() will add Teal support to your package loader, meaning that require() will be able to run .tl files.
Genius design.
ufo · 1h ago
Teal compiles to Lua text files. I believe it's compatible with both Lua 5.1 and 5.4
And though they mention it as being for third party libraries, this also seems a way to declare types for your own code in an external file, thus keeping your code as runnable Lua and benefiting from type checking too. That seems like a neat workflow for developing Neovim plugins with this: instead of having to constantly regenerate Lua from .tl files so Neovim can pick up your changes during development.
> this also seems a way to declare types for your own code in an external file, thus keeping your code as runnable Lua and benefiting from type checking too
The declaration file isn't used to typecheck the code the declaration is for. It is only for consumers of the code.
sundarurfriend · 3h ago
Ah that's a shame. I was hoping it would work via sidecar files like Ruby's RBS [1] or Python's stub files [2]
I was editing my comment during your reply, and added this:
Off-topic comment, but as an ESL speaker I just this week randomly learned that teal the color is named after the duck species Anas crecca, called (edit: common or Eurasian) teal in English.
nozzlegear · 11h ago
TIL! My wife is a photographer and she's been photographing a ton of Blue-winged Teals over the last couple months during their migration. I assumed that the ducks had been named after the color.
Sharlin · 10h ago
Cool! (Just to be clear, I meant the common, or Eurasian, teal whose iridescent green head markings the color’s apparently named after. The NA teals are closely related, although it seems they were assigned to their own genus in 2009 as it was discovered that the then-Anas was not monophyletic.)
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”.
3036e4 · 8h ago
About blue and green, I know absolutely nothing about this, but I was randomly Wikipedia-surfing a few days ago and found the long page on this topic that is interesting (but has the scary warning at the top about multiple issues).
I really want to like Lua but I just can’t. Tried Lua/Fennel/even Teal but I just can’t.
I can’t tell what it is exactly. Maybe those weird global rules? Maybe inspection of objects and metatables? Maybe the weird mix of verbose and not verbose (e.g. getting output of a process requiring popen and manual handling but then function can take more arguments than declared and whateva) or exotic control flow and structures (metatable, global env).
It’s interesting language, but I just grit my teeth every time I’m interacting with it.
No comments yet
nicoloren · 2h ago
I really like Lua and I work with it almost daily.
But, I hate luarocks. It just don't work well on Windows. And I don't know why. The management of external libraries makes Lua still too difficult to use, which is a real shame considering the qualities of this programming language.
paranoidxprod · 1h ago
Something to keep an eye out for is Lux: https://github.com/nvim-neorocks/lux. Looks like a promising replacement to Luarocks, but is still pretty early in development.
HexDecOctBin · 12h ago
Has anyone used this? Any reviews? Based on the Github issues, the type system seems to have some holes in it, but it's not obvious how bad is it in real world.
andre-la · 2h ago
I'm using it for my game
hombre_fatal · 9h ago
I used it to write a couple Pico-8 games a year or two ago since Lua + dynamic typing is a major obstacle for me managing game code over time. Teal worked well for that.
max0563 · 12h ago
This is super cool. I have been using TypeScript To Lua (https://github.com/TypeScriptToLua/TypeScriptToLua) for a little game side project and it works quite well, I am pleased with it. It does end up generating a lot of Lua code though because it has to support all of TypeScript’s features, which isn’t ideal. I’d expect Teal’s output to be much more concise Lua which has me interested.
hisham_hm · 20m ago
Teal's output is currently pretty much 1-to-1 with the input apart from removing all of the type information of course. (I've been trying hard to keep it that way so that the error messages in stack traces match the input lines without having to do source mapping.)
k__ · 4h ago
I tried it for one project, but converted it to TypeScript-to-Lua instead.
I used Lua on the backend and my frontend was already in TypeScript, so it was nice that I could reuse the backend types without conversion in the frontend.
yyx · 4h ago
I'm getting `TypeError: e is null` by opening this website in a new tab.
Firefox 138.0.1
hisham_hm · 19m ago
Please try again, shouldn't be happening, hopefully!
johnisgood · 2h ago
Same, Chromium-based browser on Linux.
koeng · 10h ago
I really love teal! Here is a 10k loc project I have in it - https://github.com/Koeng101/libB/blob/dev/src/dnadesign/dnad... - Basically, I reimplemented all my synthetic biology bioinformatics from Go into teal so that LLMs can script with it better in a hermetic environment. It's got all sorts of things like cloning simulation, codon optimization, genbank parsing, synthesis fixing, reliable sequence hashing, sequence analysis, etc. I'm pretty sure it is a more complete synbio library than anything in python, actually.
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.
hisham_hm · 25m ago
Teal creator here! Thank you for the kind words, super happy to see people being productive with it!!
On your wishlist items:
1. There are a few third-party projects that bundle Lua code. One that comes to mind is https://lrocket.codeberg.page/ — I don't know if this functionality should be brought into Teal itself, it sounds to me like something better left to the surrounding tooling?
2. Unfortunately those annoyances are part of the heterogeinity of the Lua ecosystem, but Teal tries to paper over them using the compat53 library (which, granted, is not available everywhere if you want to do a pure-Lua deployment on existing Lua environments). The --gen-target and --gen-compat flags should still help some, hopefully!
3. Not sure what you mean there -- you mean adding chunks of untyped Lua _in the same file_? I think that if you have a json.lua and a json.d.tl file, then it should use the definition file only and leave the .lua file alone. At least that's the intended behavior!
4. That's up to GitHub :) Last time I checked their docs I think they want something like 100 or 200 projects using the language for considering adding native highlighting for it on the website. But you can add a .gitattributes file to the root of your repository like this https://github.com/teal-language/tl/blob/master/.gitattribut... and at least it will display .tl files with .lua highlighting.
Again, thank you so much for the feedback!
90s_dev · 12h ago
Tuples: {number, string}
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>
hisham_hm · 18m ago
In our experience, single-element tuples are just never used in practice. There has been some discussion on how to add syntax for them, but I think it's more of a desire for orthogonality than for a practical need.
johnisgood · 2h ago
Now I am curious what {number, string, number} would be considered as.
hisham_hm · 17m ago
it's a three element tuple.
CobrastanJorji · 11h ago
This is very cool. I wonder if it works with Roblox, which is probably the environment with the largest number of Lua programmers. It certainly looks like it should work basically anywhere Lua works.
fithisux · 10h ago
The use their dialect of Lua. Luau, stuck on 5.1 (correct me if I am wrong) like LuaJit for performance reasons.
It is gradually typed, so no need to use Teal.
LoganDark · 5h ago
> Luau, stuck on 5.1 (correct me if I am wrong) like LuaJit for performance reasons.
It's not just for performance reasons, and they don't exactly have no features from newer versions. Take a look at the compatibility tables: https://luau.org/compatibility
kuruczgy · 10h ago
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?)
lolinder · 9h ago
People get this way about TypeScript too, and it always perplexes me. These projects are about adding types to untyped languages, and that comes with a few givens:
* 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.
debugnik · 7h ago
> Your type system cannot be sound.
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).
ufo · 1h ago
A tricky tradeoff is that, because Teal compiles to Lua source, adding those run-time type checks would incur some considerable overhead. I've seen other languages in this space easily run 2 or 3 times slower when run-time checks are turned on. It's an open research problem.
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.
lolinder · 1h ago
TypeScript supports runtime type assertions, but it doesn't mandate them or write them for you.
I should have said your type system cannot be sound without runtime overhead. And I don't believe that choosing automatic runtime overhead is the right move.
debugnik · 1h ago
The problem is not that it doesn't write them for you, but that `as MyType` is way too ergonomic of a syntax for unchecked assertions, whereas checked assertions require effectively parsing the structure manually with typeof checks.
TypeScript desperately needs a way to derive type-guarding functions from types (and so does every gradually-typed language). There're libraries for this but you need to define the types themselves through combinators.
kuruczgy · 8h ago
> Your type system cannot be sound. It's going to have escape hatches and exceptions because that's how dynamic languages roll.
I think you could prove that you can't construct a sound & complete type system for Lua. But just saying "Your type system cannot be sound" by itself is definitely wrong. I don't understand why people are throwing out both soundness & completeness, instead of at least retaining one (and I think the choice here is pretty obvious, a sound but incomplete type system is much more useful than an unsound one).
From Flow's website[1] (a type checker for JavaScript):
> Flow tries to be as sound and complete as possible. But because JavaScript was not designed around a type system, Flow sometimes has to make a tradeoff. When this happens Flow tends to favor soundness over completeness, ensuring that code doesn't have any bugs.
I don't understand why other type systems for dynamically typed languages cannot strive for that, and in particular I am pretty salty at TypeScript for explicitly not caring about soundness.
Why, though? Completeness matters more than soundness in practice for this kind of language, which is a large part of what gave TypeScript its edge. The only people who complain about soundness seem to be those whose approach to TypeScript is one of theoretical interests rather than practical application.
pansa2 · 10h ago
> How confident are you in the soundness of the type system?
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.
Do you know how old that is? Lua Teal has already been around for at least 5 years.
tkzed49 · 12h ago
I vote we give the name to the lua one!
90s_dev · 12h ago
Seconded.
ayrtondesozzla · 3h ago
I think you and GP both mean that this TEAL is adjacent to crptocurrency, and therefore, who cares about stepping on toes?
This heuristic works well in most cases maybe, but will lead to false positives sometimes. May I gently suggest that this might be one of those cases. Algorand is the project of this fellow
Credentials aren't faultless but they do provide a certain web of trust. If you browse the academic and professional history of this fellow, I think you'll agree.
Algorand is, I think, as serious and sincere a research project as any other.
90s_dev · 1h ago
I meant that I have a sort of affection for Lua, so it gets preferential treatment in my book, and therefore Teal ought to get the name above another relatively random project with the same name.
russellbeattie · 7h ago
Oof. What is it about the devs who prefer static typing that they insist on bolting it onto every scripting language they can? It's nearly a compulsive disorder.
There's plenty of languages with compile time type safety, just go use one of them and leave the perfectly good dynamic ones alone.
Static typing proponents need accept that dynamic typing is a perfectly valid way to write and run code: It's way less verbose, it focuses code on logic rather than syntax (a.k.a. "scripting"), it's easier to mentally parse and generally easier to both learn and use.
Inflicting types on every piece of code written is just ridiculous.
I realized my initial dislike for lua stemmed from my experience with javascript (back in the jwquery days), where maintaining large codebases felt like navigating a minefield. The lack of type system made it all too easy to introduce bugs.
But lua isn't like that. It's not weakly typed like javascript - it's more akin to pythons dynamic duck typing system. Its simplicity makes it remarkably easy to write clean maintainable code. Type checking with type is straightforward compared to python, mostly because there are only five basic types (technically seven but I've never used userdata or thread). And I even started to enjoy using metatables once I understood how and when to apply them.
That being said, lua's lack of popularity probably stems from its limited stdlib, which often feels incomplete, and the absence of a robust package manager. luarocks is a pain to work with.
All that being said, I don't really see the point of using this project.
While I do wish type annotations were a native feature, the ones provided by the lsp are good enough for me.
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!
Cannot confirm this. It might be true on selected micro benchmarks. Here are the results of the Are-we-fast-yet benchmark suite, which includes a decent set of benchmarks challenging CPU, cache and memory access: https://github.com/rochus-keller/Oberon/blob/master/testcase....
On average, the C and C++ implementations are five times faster than LuaJIT.
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.
As someone else have pointed it out, they are cherry picked: https://luajit.org/extensions.html.
LuaJIT is missing bignums, ints that aren’t floats, bit operations, and native utf8 handling, but it can pretty easily be extended with libraries, ffi and metatabling. (I actually made a working bignum library that integrates with gmp, but it has a memory leak somewhere and it’s a rabbit hole/bikeshedding project at this point…)
LLM assistance helps hugely and I really like YueScript’s syntax additions. You can point any LLM at a syntax describing webpage and it will pretty much write that language for you…
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"?
[0] https://youtu.be/Uq_8bckDxaU?t=1618
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.
Anyway, that has not stopped large parts of the JavaScript ecosystem -- notably Angular -- from using an experimental variant of decorators, such as the one provided by TypeScript. [2]
[1] https://github.com/tc39/proposal-decorators
[2] https://github.com/angular/angular/issues/48096
[0]: https://github.com/tc39/proposal-enum
Teal still compiles all those things into plain Lua tables, it's just that the type system has different table subtypes for better type checking. I think the variable scoping is also the same as regular Lua?
[1] https://github.com/devcat-studio/kailua/
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.
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
Looks similar to Teal.
This is relatively exciting.
Also, called it!
Disappointed that it maintains syntactic Lua compatibility. Would have been a good time for a clean slate on the shoulders of hindsight.
Is that true ... you can't have typed tables without giving up tables as a data structure?
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.
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...
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.
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.
- tables being used for both objects and arrays can create a lot of confusion, especially when you have some integer keys, but not all, and especially when they are not consecutive or one of them is 0 - indexes start at 1 - assigning nil deinitializes variables/entries instead of assigning the value `nil` (this becomes especially bad if you mistakingly try to use nil as a value in an array/table) - nil and false are falsy, but not 0, which instead is truthy
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.)
But, equivalently, of course I'm going to criticize a hammer if it's literally covered in warts making it difficult to grasp without slipping. (or, if the gun I'm trying to use keeps firing bullets into my foot when I'm aiming down range.)
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 ...
https://fennel-lang.org/
I don't think that's true. It's a very embedded language. Its use in video games and video game modding alone would outnumber the number of people directly writing assembly to achieve things.
LuaJIT is famously on 5.1 with no signs of moving.
Genius design.
to be used via `global_env_def` described in https://teal-language.org/book/declaration_files.html
And though they mention it as being for third party libraries, this also seems a way to declare types for your own code in an external file, thus keeping your code as runnable Lua and benefiting from type checking too. That seems like a neat workflow for developing Neovim plugins with this: instead of having to constantly regenerate Lua from .tl files so Neovim can pick up your changes during development.
Edit: or maybe https://github.com/teal-language/tl#loading-teal-code-from-l... this is the easier way to do it. `require` and use `loader` during development, generate the Lua once things are somewhat stable.
The declaration file isn't used to typecheck the code the declaration is for. It is only for consumers of the code.
I was editing my comment during your reply, and added this:
> or maybe https://github.com/teal-language/tl#loading-teal-code-from-l... this is the easier way to do it. `require` and use `loader` during development, generate the Lua once things are somewhat stable.
Does that sound like the right idea then?
[1] https://github.com/ruby/rbs [2] https://mypy.readthedocs.io/en/stable/stubs.html
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”.
https://en.wikipedia.org/wiki/Blue%E2%80%93green_distinction...
I can’t tell what it is exactly. Maybe those weird global rules? Maybe inspection of objects and metatables? Maybe the weird mix of verbose and not verbose (e.g. getting output of a process requiring popen and manual handling but then function can take more arguments than declared and whateva) or exotic control flow and structures (metatable, global env).
It’s interesting language, but I just grit my teeth every time I’m interacting with it.
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I used Lua on the backend and my frontend was already in TypeScript, so it was nice that I could reuse the backend types without conversion in the frontend.
Firefox 138.0.1
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.
On your wishlist items:
1. There are a few third-party projects that bundle Lua code. One that comes to mind is https://lrocket.codeberg.page/ — I don't know if this functionality should be brought into Teal itself, it sounds to me like something better left to the surrounding tooling?
2. Unfortunately those annoyances are part of the heterogeinity of the Lua ecosystem, but Teal tries to paper over them using the compat53 library (which, granted, is not available everywhere if you want to do a pure-Lua deployment on existing Lua environments). The --gen-target and --gen-compat flags should still help some, hopefully!
3. Not sure what you mean there -- you mean adding chunks of untyped Lua _in the same file_? I think that if you have a json.lua and a json.d.tl file, then it should use the definition file only and leave the .lua file alone. At least that's the intended behavior!
4. That's up to GitHub :) Last time I checked their docs I think they want something like 100 or 200 projects using the language for considering adding native highlighting for it on the website. But you can add a .gitattributes file to the root of your repository like this https://github.com/teal-language/tl/blob/master/.gitattribut... and at least it will display .tl files with .lua highlighting.
Again, thank you so much for the feedback!
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>
It is gradually typed, so no need to use Teal.
It's not just for performance reasons, and they don't exactly have no features from newer versions. Take a look at the compatibility tables: https://luau.org/compatibility
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.
I should have said your type system cannot be sound without runtime overhead. And I don't believe that choosing automatic runtime overhead is the right move.
TypeScript desperately needs a way to derive type-guarding functions from types (and so does every gradually-typed language). There're libraries for this but you need to define the types themselves through combinators.
I think you could prove that you can't construct a sound & complete type system for Lua. But just saying "Your type system cannot be sound" by itself is definitely wrong. I don't understand why people are throwing out both soundness & completeness, instead of at least retaining one (and I think the choice here is pretty obvious, a sound but incomplete type system is much more useful than an unsound one).
From Flow's website[1] (a type checker for JavaScript):
> Flow tries to be as sound and complete as possible. But because JavaScript was not designed around a type system, Flow sometimes has to make a tradeoff. When this happens Flow tends to favor soundness over completeness, ensuring that code doesn't have any bugs.
I don't understand why other type systems for dynamically typed languages cannot strive for that, and in particular I am pretty salty at TypeScript for explicitly not caring about soundness.
[1]: https://flow.org/en/docs/lang/types-and-expressions/#toc-sou...
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.
This heuristic works well in most cases maybe, but will lead to false positives sometimes. May I gently suggest that this might be one of those cases. Algorand is the project of this fellow
https://en.m.wikipedia.org/wiki/Silvio_Micali
Credentials aren't faultless but they do provide a certain web of trust. If you browse the academic and professional history of this fellow, I think you'll agree.
Algorand is, I think, as serious and sincere a research project as any other.
There's plenty of languages with compile time type safety, just go use one of them and leave the perfectly good dynamic ones alone.
Static typing proponents need accept that dynamic typing is a perfectly valid way to write and run code: It's way less verbose, it focuses code on logic rather than syntax (a.k.a. "scripting"), it's easier to mentally parse and generally easier to both learn and use.
Inflicting types on every piece of code written is just ridiculous.