Bagel-rs Alternatives

bagel-rs reviews and mentions

• Why I love Rust for tokenising and parsing
  12 projects | news.ycombinator.com | 7 Nov 2024

  Yup! You can find it here: https://github.com/brundonsmith/bagel-rs/blob/master/src/mod...

  [trying to remind myself how this works because it's been a while]

  So it's got macros for defining "union types", which combine a bunch of individual structs into an enum with same-name variants, and implement From and TryFrom to box/unbox the structs in their group's enum

  ASTInner is a struct that holds the Any (all possible AST nodes) enum in its `details` field, alongside some other info we want all AST nodes to have

  And then AST is a struct that holds (1) an RC, and (2) a PhantomData, where TKind is the (hierarchical) type of AST struct that it's known to contain

  AST can then be:

  1. Downcast to a TKind (basically just unboxing it)

  2. Upcast to an AST

  3. Recast to a different AST (changing the box's PhantomData type but not actually transforming the value). This uses trait implementations (implemented by the macros) to automatically know which parent types it can be "upwardly casted to", and which more-specific types it can try and be casted to

  The above three methods also have try_ versions

  What this means then is you can write functions against, eg, AST. You will have to pass an AST, but eg. an AST can be infallibly recast to an AST, but an AST can only try_recast to AST (returning an Option>)

  I worked in this codebase for a while and the dev experience was actually quite nice once I got all this set up. But figuring it out in the first place was a nightmare

  I'm wondering now if it would be possible/worthwhile to extract it into a crate