Stage 2.7 Draft / December 3, 2024

Iterator Sequencing

Let iterables be a new empty List.
2. For each element item of items, do
1. If item is not an Object, throw a TypeError exception.
2. Let method be ? GetMethod(item, %Symbol.iterator%).
3. If method is undefined, throw a TypeError exception.
4. Append the Record { [[OpenMethod]]: method, [[Iterable]]: item } to iterables.
3. Let closure be a new Abstract Closure with no parameters that captures iterables and performs the following steps when called:
1. 1. For each Record iterable of iterables, do
  1. Let iter be ? Call(iterable.[[OpenMethod]], iterable.[[Iterable]]).
  2. If iter is not an Object, throw a TypeError exception.
  3. Let iteratorRecord be ? GetIteratorDirect(iter).
  4. Let innerAlive be true.
  5. 5. Repeat, while innerAlive is true,
    1. Let iteratorResult be ? IteratorStep(iteratorRecord).
    2. 2. If iteratorResult is done, then
      1. Perform ? IteratorValue(iteratorResult).
      2. Set innerAlive to false.
    3. 3. Else,
      1. Let completion be Completion(GeneratorYield(iteratorResult)).
      2. If completion is an abrupt completion, then
        Return ? IteratorClose(iteratorRecord, completion).
2. Return ReturnCompletion(undefined).
Let gen be CreateIteratorFromClosure(closure, "Iterator Helper", %IteratorHelperPrototype%, « [[UnderlyingIterators]] »).
Set gen.[[UnderlyingIterators]] to a new empty List.
Return gen.