pub fn for_await(
  in iterator: AsyncIterator(a, return, next),
  run fun: fn(a) -> any,
) -> promise.Promise(Nil)

pub fn new(
  next: fn(option.Option(next)) -> promise.Promise(
    iterator_result.IteratorResult(a, return),
  ),
) -> AsyncIterator(a, return, next)

pub fn next(
  iterator: AsyncIterator(a, return, next),
) -> promise.Promise(iterator_result.IteratorResult(a, return))

pub fn next_with(
  iterator: AsyncIterator(a, return, next),
  value: next,
) -> promise.Promise(iterator_result.IteratorResult(a, return))

pub fn return(
  iterator: AsyncIterator(a, return, next),
) -> promise.Promise(
  Result(iterator_result.IteratorResult(a, return), Nil),
)

pub fn return_with(
  iterator: AsyncIterator(a, return, next),
  value: return,
) -> promise.Promise(
  Result(iterator_result.IteratorResult(a, return), Nil),
)

pub fn throw(
  iterator: AsyncIterator(a, return, next),
  reason reason: e,
) -> promise.Promise(
  Result(iterator_result.IteratorResult(a, return), Nil),
)

pub fn with_return(
  iterator: AsyncIterator(a, return, next),
  return: fn(option.Option(return)) -> promise.Promise(
    iterator_result.IteratorResult(a, return),
  ),
) -> AsyncIterator(a, return, next)

pub fn with_throw(
  iterator: AsyncIterator(a, return, next),
  throw: fn(e) -> promise.Promise(
    iterator_result.IteratorResult(a, return),
  ),
) -> AsyncIterator(a, return, next)