This started out as a learning project to teach myself Rust. It has grown into a decently substantial piece of software and I've learned quite a bit in the process!
Some neat things:
+ A garbage collector that can store dynamically sized types without any double-indirection (i.e. I have my own Box implementation with manual alloc/dealloc)
+ The smart pointer used to reference GCed data is a thin pointer. The ptr metadata needed for DSTs is stored in the GC allocation itself, so that the GC smart pointer is just a single usize wide. This allows me to keep the core value enum Variant down to 16 bytes (8 bytes for data, the enum discriminant, and some padding).
+ The GC also supports weak references!
+ Statically dispatched type object model using a newtype wrapper and Rust's declarative macros. Ok, what that means is that I have a MetaObject trait that I can use to easily add new data types and define the behavior for specific types. Similar idea to Python's PyTypeObject though very different in implementation. However, I don't resort to dynamic dispatch or trait objects despite working with dynamically type data. Instead, I have a newtype wrapper over the core value enum Variant that statically dispatches to each of the enum branches! And then a few macros that minimize the boilerplate required if I want to add a new branch to Variant or a new method to MetaObject (just a single line in each case).
+ Different string representations! This was inspired by the flexstr crate. Strings that are short enough to fit inside a Variant are "inlined" directly in the value. Longer strings are either GCed or interned in a thread-local string table. All identifiers are interned.
+ An efficient implementation of closures inspired by Lua's upvalues.
The language is still pretty WIP. I'm planning to add an import system, a small standard library, and a few other things
(Yes, the name might not be the best, being also used by a well-known ReST docs generator, I'll take suggestions. I do like the name though, both as a reference to the mythological creature and the cat :D)