:</span>
    <span class="comment">// Samples type is int</span>
    <span class="keyword">using</span> <span class="identifier">sample</span><span class="special">=</span><span class="keyword">int</span><span class="special">;</span>
    <span class="keyword">enum</span> <span class="special">{</span> <span class="identifier">arity</span> <span class="special">=</span> <span class="number">1</span> <span class="special">};</span>

    <span class="keyword">struct</span> <span class="identifier">iterator</s