type _R<T> = [T] extends [{ _R: (_: infer R) => void }] ? R : never;
type _E<T> = [T] extends [{ _E: () => infer E }] ? E : never;
type _A<T> = [T] extends [{ _A: () => infer A }] ? A : never;

interface Sync<R, E, A> {
  _R: (_: R) => void;
  _E: () => E;
  _A: () => A;
}

type R = _R<Sync<number, string, void>>;
type E = _E<Sync<number, string, void>>;
type A = _A<Sync<number, string, void>>;