(Elem, AccIn)</code> on successive elements <code>A</code> of <code>Iterator</code>,
  starting with <code>AccIn</code> == <code>Acc0</code>. <code>Fun/2</code> must return a new
  accumulator, which is passed to the next call. The function returns
  the final value of the accumulator. <code>Acc0</code> is returned if the  
iterator is empty.</p>
 
  The iterator will be fully evaluated, infinite iterators will never
  return.</p>

<h3 class="function"><a name="foldr-3">foldr/3</a></h3>
<div class="spec">
<