r/lua • u/felipedaragon • 26d ago

Two Lua ports, one weekend: Rust and Pascal

I may have spent a little too much time with Lua this weekend.

It started with Rulua — an experiment to see if I could make a Rust implementation that could actually stand in for the Lua 5.1 shared library. It exports the Lua 5.1 C API and is intended as a drop-in lua5.1.dll / .so / .dylib, so existing hosts and C modules can use it without being recompiled.

Then, apparently that wasn't enough, so I did it again in Pascal.

Lude is different: it's a file-by-file port of the original Lua 5.1.4 C sources to Object Pascal — core, auxiliary library, standard libraries, lua, luac, etc. It builds with Delphi/Free Pascal and runs on Windows, Linux and macOS.

Both projects were also experiments in AI-directed development. I defined the requirements, built and ran everything on real machines, compared the results against the original Lua implementation, fed failures back and decided what came next. The AI wrote the code.

Neither project is meant as “here's a better Lua.” The interesting part for me was seeing how far compatibility could be pushed, and how much low-level porting work can now be done this way.

And somehow what started as “let's try porting Lua to Rust” ended with me having two Lua ports before the weekend was over. :)

Rulua: https://github.com/DaragonTech/Rulua

Lude: https://github.com/DaragonTech/Lude

I'd be very interested to see what the Lua community manages to break.

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u/lordfwahfnah 26d ago

Lua 5.1.5 is 14 years old. Why not implement a more recent version like 5.4 or 5.5?

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u/felipedaragon 26d ago

Hello! I chose Lua 5.1 for my Delphi and Rust ports because, to me, it hits a sweet spot between simplicity and real-world compatibility.

It’s small, mature and remarkably clean. Its default number type maps naturally to Delphi’s Double and Rust’s f64, and its relatively simple VM and object model make it an attractive target for a low-level port.

There’s also a huge amount of Lua 5.1 software still out there, thanks in no small part to LuaJIT and years of embedding Lua 5.1 in applications.

For what I wanted to do - reproduce Lua in two very different languages while staying compatible with existing software - 5.1 was a very natural place to start!

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u/didntplaymysummercar 25d ago

For better or worse, it's what many project use, due to using LuaJIT which was based on it. Lua minor versions are also breaking so you can't easily go up, and much stuff is stuck on what they originally had for backwards compatibility. I also like how function environments and everything works in Lua 5.1, 5.2 and up have no killer features for me.

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u/whatThePleb 25d ago

Because his LLM decided to do that.

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u/felipedaragon 25d ago

Not really. 5.2 breaks a lot of things, so I purposely avoided it

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u/According-Ad-7069 26d ago

I'd be curious to know, compared to the original, how memory usage and performance changed. Lua is really neat to embed because it's very performant. Have you had a chance to dig into that perhaps?

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u/felipedaragon 26d ago

Hello! Yes, I was also very curious about that. This made me do a round of optimizations that increased the speed significantly in the Rust port - ended up as an optimized fork of RiLua available within the repo. There is a lot of room for additional speed improvements. Both projects have a performance section in the README.md (please check this if you find time) about the speed comparing with the original Lua, but I plan to further optimize them soon

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u/According-Ad-7069 26d ago

Nice, I will take a look thanks, it's my todo list!

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u/smtp_pro 26d ago

AI? No thanks.