of
this stream.
For each element, the value is updated to the result of calling
<code>combine</code> with the previous value and the element.</p>
<p>When this stream is done, the returned future is completed with
the value at that time.
For an empty stream, the future is completed with <code>initialValue</code>.</p>
<p>If this stream emits an error, or the call to <code>combine</code> throws,
the returned future is completed with that error,
and processing is stopped.</p>
    </section>
    
    <section cl