Got most of a port of centi-typescript to Rust going!

[simonbuchan]

The repo: https://github.com/simonbuchan/tts ("Tiny TypeScript")

Thought this would be a good way to really prove I understand what's going on, especially as Rust is very angry at you for trying a lot of the patterns in this repo!

Pretty dang bare, doesn't have a lot of stuff yet, especially notably:

• checking generic instantiation - need to figure out the types there since I can't just cast it :P
• errors don't elaborate types (so you mostly get just Def(#2)) - but I have a plan
• doesn't (and probably won't) transform and emit javascript

Ended up flattening the syntax and symbol table trees into flat lists so I could use indices (the typical Rust solution to messy structures), so it's often horribly verbose right now. The syntax table is especially interesting as it's so heterogenous - I ended up using a macro to generate wrapper types, resulting in some pretty messy internals. There's a lot to improve there, in particular generating a proper visitor - I ended up having to hand-write a tree dumper!

Similarly, this drops the syntax parent pointers and only keeps symbol table parent pointers - good enough for the current uses.

The binder and checkers had a bit of back-and-forwards about handling lifetime checking - I don't think it's quite perfect, but it's good enough for now. (It was pretty gnarly at points!)

I suspect that a lot of the recursive descent that the binder and checker does could be completely flattened with a flat syntax / symbol list - they both end up being post-order traversals of the logical tree, so it seems like there should be a good way to take advantage and just do some sort of direct mapping.

[simonbuchan]

Improved error output and fixed comparing signature argument lengths, but inference is not working at all...
But getting quite close to parity! (except emit)