Rulox

This is my implementation of Lox, following the Crafting Interpreters book by Bob Nystrom. It is supports all features of jlox except classes. Why Ruby? Because I hadn't used it in any recent project of mine and I miss it. The book doesn't cover a ruby implementation, but Ruby is simple enough that I should still be able to follow the instructions for writing jlox.

Although I was following the instructions for jlox when writing this, the code inside can differ quite a bit. Some things are just better done differently in Ruby. I also changed a lot of variable names and function layouts to my likings. I tried to avoid real OOP, because I am more into FP. I only used the code mentioned in the book as a guide, like how it's supposed to be used. Even though the relative behavior of rulox looks like jlox, you should not use rulox as an example of how to write jlox in Ruby.

I did add some extra stuff, like adding a ternary operator. Making this interpreter is like an exercise to me, and it wouldn't be challenging if I didn't try to do some stuff on my own.

I wanted to write my first interpreter in a scripting language, because that seemed more fun and less serious. But it quickly made me realize that I have adapted so much to the type systems of C and Rust, that I can hardly go without.

Additional stuff (that weren't challenges in the book):

• Both or, and and ||, && work
• Ternary operator
• ruby keyword to evaluate ruby code with (which is fun because now you can recursively use the same interpreter)
• Escaping with \ in strings
• += and -= operators

Run with ruby src/main.rb <filename> or without a filename for the REPL

Anyway this project was just to get my feet wet, you can expect more PLs from me in the future. Possibly with actuale usecases

Edit: It might be interesting to rewrite this to Crystal which is an LLVM based language with a syntax based on RubySpec This means I could write a standard library in C with relative ease, and the type system would be appreciated. Sadly currently crystal is missing some features I like and the devs refuse to accept my PRs

File IO

Rulox has a couple of really basic native functions. For file IO there are 3 functions based around file descriptors. This way you can use just 3 functions to read/write files, write to stdout and stderr, and read input from stdin.

//Write to a file
var fd =  openfd("myfile", "w");
writefd(fd, "My data");

//Read the same file
fd = openfd("myfile", "r");
print readfd(fd);

//Read data from stdin
print readfd(0);

Performance

In the first section of the chapter Chunks of Bytecode, Bob says that on his laptop jlox takes 72 seconds to calculate the 40th fibonacci number. I ran the same code with rulox, and with some calculations I found that calculating the same number in rulox would take around 77.7 minutes. I am not sure why, or how rulox is that fucking slow but it is.

That's with my cpu overclocked to 3.7Ghz, though somehow Ruby isn't taking total cpu time. More like 25% of its core.