cactusref VS luau

Absolutely. I have seen some pretty cool concepts in Rust for memory cleanup; not just garbage collection, but deterministic reference cycle removal by cactusref. And the fun thing about these is that you still get all of Rust's zero-cost abstractions and epic modern language design.

I've put together a WIP PR to experiment with a safe adoption API: https://github.com/artichoke/cactusref/pull/47. This allows the doubly linked list example to be implemented in safe code without leaks. I didn't even think this was possible! Thanks for making me think!

It does indeed still work that way! We even still support the old, in-house VM, known as LSO2: https://wiki.secondlife.com/wiki/LSO

We're hard at work adding Luau (https://luau.org) as a supported language for both in-world scripting as well as client/viewer-side scripting. As a handy byproduct of that, LSL will also gain the ability to be compiled to Luau bytecode, allowing us to eventually (someday, at least) shed any need for our custom-patched version of Mono 2.6. More juicy details here: https://wiki.secondlife.com/wiki/Lua_FAQ

Source: I work at Linden Lab. If these sorts of things excite anyone, we're hiring!

I love Lua but I also prefer static types, so this looks great. I’ve used Luau[1] in the past which has gradual typing, but that’s less useful unless it’s enforced as a coding standard.

[1] https://luau-lang.org/

>> the VM assumes that the bytecode was generated by the Luau compiler (which never produces invalid/unsafe bytecode)

To that end they have a basic bytecode verifier (only used in debug mode / asserts are enabled) that validates the compiler only outputs valid bytecode, and continuously fuzz the compiler to make sure those asserts can't be triggered. See https://github.com/luau-lang/luau/blob/0d2688844ab285af1ef52...

It's fairly robust (and Luau bytecode isn't _that_ complex,) but they made the right decision disallowing direct bytecode execution.

For anyone interested:

Roblox's Luau: https://luau-lang.org/

> Luau is a fast, small, safe, gradually typed embeddable scripting language derived from Lua.

> Around 2006, Roblox started using Lua 5.1 as a scripting language for games. Over the years the runtime had to be tweaked to provide a safe, secure sandboxed environment; we gradually started accumulating small library changes and tweaks.

As far as I can tell, they aren't.

http://lua-users.org/wiki/SandBoxes

There is a lot of information there, but it doesn't handle resource exhaustion, execution time limits or give any guarantees. It does indicate that it's possible, and has a decent example of the most restrictive setup, which is a good start. But I would for example compare it with Luau's SECURITY.md.

From https://github.com/luau-lang/luau/blob/master/SECURITY.md:

> Luau provides a safe sandbox that scripts can not escape from, short of vulnerabilities in custom C functions exposed by the host. This includes the virtual machine and builtin libraries. Notably this currently does not include the work-in-progress native code generation facilities.

> Any source code can not result in memory safety errors or crashes during its compilation or execution. Violations of memory safety are considered vulnerabilities.

> Note that Luau does not provide termination guarantees - some code may exhaust CPU or RAM resources on the system during compilation or execution.

So, even luau will have trouble with untrusted code, but it specifies exactly what happens and so on. I think that's fair enough.

Alternatively, Luau is a well-supported Lua variant with type checking and performance improvements, aimed more towards being a sandboxed embedded scripting environment.

https://luau-lang.org/

If you need Lua but also type-safety, how about Luau [1] then?

[1] https://luau-lang.org/

I had the pleasure of working with Lua 5.1 back in the late noughties. For me it's replaced Tcl whenever I want something I can configure above a C library. At the time I used it I found it quite nice but I'll also not forget the hours I wasted tracking down nil table corruptions which could have easily been caught by a type checker.

I had some hope that Luau https://luau-lang.org or Teal https://github.com/teal-language/tl would make things better but with the following example

    function foo(x: number): string

Looking at other replies here, I can see I wasn't the only one who didn't realize there is Lua and Luau. Luau is an extension of Lua: https://luau-lang.org/

> Luau is syntactically backwards-compatible with Lua 5.1 (code that is valid Lua 5.1 is also valid Luau); however, we have extended the language with a set of syntactical features that make the language more familiar and ergonomic.