function all<T>(
  tasks: T,
  options?: CollectOptions<true>,
): Task<
  { [K in string | number | symbol]: InferTaskOk<T[K]> },
  InferTaskErr<T[number]>,
  InferTaskDeps<T[number]>
>;

const result = await run(all([fetchUser, fetchPosts, fetchComments]));
if (!result.ok) return result;
const [user, posts, comments] = result.value;

function all<T>(
  tasks: T,
  options?: CollectOptions<true>,
): Task<
  { [P in string | number | symbol]: InferTaskOk<T[P]> },
  [keyof T] extends [never] ? never : InferTaskErr<T[keyof T]>,
  [keyof T] extends [never] ? unknown : InferTaskDeps<T[keyof T]>
>;

const result = await run(all({ user: fetchUser, posts: fetchPosts }));
if (!result.ok) return result;
const { user, posts } = result.value;

function all<T, E, D>(
  tasks: Iterable<Task<T, E, D>>,
  options?: CollectOptions<true>,
): Task<readonly T[], E, D>;

const urls: ReadonlyArray<string> = getUrls();
const result = await run(map(urls, fetchUrl));
if (!result.ok) return result;
// result.value: ReadonlyArray<Response>

function all<T, E, D>(
  tasks: readonly [Task<T, E, D>, Task<T, E, D>],
  options?: CollectOptions<true>,
): Task<readonly [T, T], E, D>;

const tasks: NonEmptyReadonlyArray<Task<Response, FetchError>> = [
  fetchUrl("/a"),
  fetchUrl("/b"),
];
const result = await run(all(tasks));
if (!result.ok) return result;
// result.value: NonEmptyReadonlyArray<Response>

function all<T, E, D>(
  tasks:
    | Iterable<Task<T, E, D>, any, any>
    | Readonly<Record<string, Task<T, E, D>>>,
  options: CollectOptions<false>,
): Task<void, E, D>;

const result = await run(all(tasks, { collect: false }));
// result.value: void