redmoon

A Rust implementation of Lua. NOT PRODUCTION READY. Mostly an excuse to hack with Rust and learn a lot.

Will it ever be production ready?

That would be nice. I am thankfully at a point where it is easier to discuss what is missing versus what is here. However, the missing pieces are a pretty big deal:

• Garbage collection: The collectgarbage function is implemented. Now I just have to figure out when to call it.

• Bytecode generation: Redmoon's current interpreter has no bytecode generation; Instead it interprets the syntax tree of the program. I am eager to start work on using proper bytecode. There's always more to learn!

• Goto statements and labels: This is a side effect of not using bytecode, meaning this feature will be very hard to implement as is. I plan to wait on adding goto's until I have a bytecode-based virtual machine.

• Generic for loops: Numeric for loops have been implemented at the time of writing.

• All operations (and all metamethods): I have the most common binary operators implemented (addition, division, comparison, etc.) but a few are still missing i.e. bitwise shifting. Metamethods do exist for most of the operators, though that is a slightly less complete list.

• Standard library: The print, setmetatable, and collectgarbage functions are there, but that's it.

Inspiration

A few months ago, I tried to compile Lua (written in C) to WebAssembly. I learned that this would be very difficult because Lua uses the setjmp and longjmp functions, which at the moment cannot be compiled to WASM. The only way to get Lua on the web was to use Emscripten, which simulates a POSIX environment with JavaScript and implements those functions in a very expensive way. The frustration I felt led me to consider reimplementing Lua in Rust, which has first-class WebAssembly support.

Starting this project also gave me excuses to finally learn three subjects in which I have long been interested: Lua, Rust, and compiler/interpreter development. Working on Redmoon made me a functioning Rust developer, and since Rust forced me to do things the "right" way, it probably made me a better developer in general.

Prior Art

I owe a large debt to Robert Nystrom. His book Crafting Interpreters helped me wrap my head around basic concepts such as tokenization, parsing, and recursive descent. It's entertaining, well thought-out, and free! I would recommend this book to anyone interested in knowing how programming languages work. (Buy a copy if you can)

If you are looking for other projects like this, at the very least there's Lua in Rust. This project has a lot going for it that this one does not, like proper garbage collection, and its README has an extensive list of features (and soon-to-be features) that I have found helpful whenever I am measuring progress of my project.