How Building a Conlang Editor Taught Me What Tagged Unions Can Actually Be In Typescript

I'm building a text editor for constructed languages. The kind of thing where you define phonological rules, morphology tables, and interlinear glossing, and the editor interprets your grammar in real time to produce translations and grammatical scores. It is absurdly niche. I love it. The problem is, a project like that needs an incremental parser, and TypeScript makes incremental parsing in a type-safe way genuinely painful. You end up with these sprawling discriminated unions full of ceremony