TS narrows union types cases based on conditionals like "if" (called discriminated unions in the docs in the past), and supports exhaustiveness checks. How do they differ in functionality from sum types?
Supports exhaustiveness checks only if you explicitly opt-in it (by coding to pattern where you use helper function that accepts `never` type). "Dicriminated Unions Type"/"Sum Types" feels very hacky there, at least syntax-wise, because it is constraint by being "JS + types" language. It's remarkable what Typescript can do, but having native Discriminated Unions in JS (hence in TS too) would be much more ergonomic and powerful.
