   <code>initialResult</code> is passed to <code>nextPartialResult</code> the first time the
    closure is executed.
  <strong>nextPartialResult:</strong> A closure that combines an accumulating value and
    an element of the sequence into a new accumulating value, to be used
    in the next call of the <code>nextPartialResult</code> closure or returned to
    the caller.
<strong>Returns:</strong> The final accumulated value. If the sequence has no elements,
  the result is <code>initialResult</code>.</p>