// library code for non-generic discriminated unions export type ReplaceReturnType<F, R> = F extends (…args: infer Args) => any ? (…args: Args) => R : never; export type TaggedUnionFactory<TUF, R> = { [K in keyof TUF]: ReplaceReturnType<TUF[K], R>; }; // for monomorphic types this just works well const _actionResult = { failure: (message: string) => ({ kind: “failure”, message } as const), value: (value: number) => ({ kind: “result”, value } as const), }; export type ActionResult = ReturnType< typeof _actionResult[keyof typeof _actionResult] >; export const actionResult: TaggedUnionFactory< typeof _actionResult, ActionResult > = _actionResult; // For generic types you have to type the usage sites but it’s still pretty good export const status = { loading: () => ({ kind: “loading” } as const), success: <V>(value: V) => ({ kind: “success”, value } as const), error: <E>(error: E) => ({ kind: “er