rlox

An implementation of the Lox language from Crafting Interpreters in Rust, up to the end of Chapter 29.

This is a very literal conversion into Rust -- there's a lot of avoidable unsafe, and a lot of very unidiomatic code.

I have some grand designs I may never get to for making this more idiomatic, in another repo where the language might diverge from lox a fair bit.

Chapter 30 is on optimizations which didn't seem worth implementing if I'm going to tear this up anyway.

Building and running

I wrote this with Rust 1.55 on stable, and everything's handled by cargo.

I don't recommend using this for much of anything. While the book's tests pass, I would be shocked if there weren't a lot of bugs still hiding in there.

Changes from the book

There were a few places where I made changes to try and avoid things Rust hates when it was clear enough that the deviations would be worthwhile and likely wouldn't have unforeseen consequences for later chapters.

• We don't have a global VM instance.
• Allocation (and freeing) of objects is a bit different.
• We have a Context instead of a bunch of global state for the compiler.
• I used a Vec instead of an internal linked list in a few places
  • For the Compiler stack, instead of enclosing.
  • In the VM to track open upvalues.
  • GC is paused when compiling. This is so we don't need to worry about the partially-compiled objects being collected, without needing to feed the compiler state back into the heap on every allocation to mark those roots.

Output should be identical, so you can use the test suite from Crafting Interpreters.

There are a cargo features you can build with to print some extra info at runtime: debug_trace, debug_log_gc. There's a debug_stress_gc which does a full collection on every allocation (when not paused) as well.