entifier">Input</span></code>. The functor
                  must meet certain requirements. It must have a typedef called
                  <code class="computeroutput"><span class="identifier">result_type</span></code> which
                  should be the type returned from <code class="computeroutput"><span class="keyword">operator</span><span class="special">()</span></code>. Also, since an input policy
                  needs a way to determine when the end of input has been reached,
                 