Implement lexing/parsing

[DylanSp]

Probably use Ohm; see links in docs/resources.md.

[DylanSp]

May want to write some helper functions for constructing instances of the AST types - see how difficult it ends up being just using the variant library's API.

[DylanSp]

Instead of Ohm, maybe use tree-sitter, to take advantage of its larger ecosystem:

• https://tree-sitter.github.io/tree-sitter/
• Node bindings (include type definitions) - https://github.com/tree-sitter/node-tree-sitter
• Writing a tree-sitter grammar- https://siraben.dev/2022/03/01/tree-sitter.html

Apparently what tree-sitter outputs is closer to a concrete syntax tree - I may want a pass that consumes that and generates an AST using my types.

[DylanSp]

Notes on testing:

• Probably test lexer/parser together (depending on how tree-sitter or Ohm works)
• For initial tests (before I implement evaluation):
  • Tests for successful parses should just pass if they successfully parse, don't check the exact structure of the resulting AST.
  • Tests for failed parses should check the exact error.

[DylanSp]

Example of using tree-sitter (not sure if directly applicable to parser): https://siraben.dev/2022/03/22/tree-sitter-linter.html