Having a look at integrating rowan/logos/lalrpop

[ratmice]

For the unicode ↔ ascii formatter to work it needs a form of concrete syntax tree,
rowan seems like the thing to use, and seems fairly straightforward to integrate with logos...

• lexer iterator iterating over rowan SyntaxKinds.

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• parser, the main difficulty here is that lalrpop wants an enum, and it seems silly sending lalrpop an,

pub enum RowanToken {
  Token(lex::LexToken, SmolStr) 
}

It's solidly ugly to pattern match in lalrpop but it does seems to work...

Bottom-up

The current GreenNodeBuilder seems primarily geared towards top-down parsers,
the path of least resistence in lalrpop is bottom-up.

Lifetimes:

Returning from the parser, via e.g. GreenNodeBuilder::finish currently doesn't work,
It seems something like the NodeCache (which I think is private), might be a usable API for bottom-up construction, and fix this too, essentially building iterators from the bottom up, I imagine for this would have to return [Leaf;1], at the bottom...

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• ensure behavior is well defined.

[ratmice]

I think this is pretty much stalled until i can get bottom-up construction and lifetimes