public func reduce<Result>(
    _ initialResult: Result,
    _ nextPartialResult:
      (_ partialResult: Result, Element) async throws -> Result
  ) async rethrows -> Result {
    var accumulator = initialResult
    var iterator = makeAsyncIterator()
    while let element = try await iterator.next() {
      accumulator = try await nextPartialResult(accumulator, element)
    }
    return accumulator
  }

try await iterator.next()