/a></h2>
<div class="highlight-cpp"><div class="highlight"><pre><span class="cp">#include</span> <span class="cpf">&lt;boost/hof.hpp&gt;</span><span class="cp"></span>
<span class="cp">#include</span> <span class="cpf">&lt;cassert&gt;</span><span class="cp"></span>
<span class="k">using</span> <span class="k">namespace</span> <span class="n">boost</span><span class="o">::</span><span class="n">hof</span><span class="p">;</span>

<span class="k">struct</span> <span class="n">sum</span>
<span class="p">{</spa