AST Syntax Highlighting with Optics

Would it be possible, and feasible, to express syntax highlighting rules via optics?

Current Achievment

Given an Abstract Syntax Tree stub of this form:

let ast = Root(block: .blockquote(.table(.code("Hello"))))

We can express getting to the inline .code inside a .table inside a .blockquote from the document root like so:

let deepReach = Root.blockLens
  >>> /BlockToken.blockquote
  >>> /BlockToken.table
  >>> /InlineToken.code

let value = deepReach.tryGet(ast) // → "Hello"

References and Inspiration

• Yasuhiro Inami: “Make your own code formatter in Swift – iOS Conf SG 2019”, 2019-01-20, https://www.youtube.com/watch?v=_F9KcXSLc_s
  • Inami’s Actomaton introduced me to CasePath: https://github.com/Actomaton/Actomaton
• “Lenses and prisms in Swift” comes with some great examples; the “box type” AffineTraversal wasn’t part of that, though ;(

GitHub

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