n class="identifier">Expr</span><span class="special">&gt;</span>
<span class="comment">// Calculate the result type: our transformed AST</span>
<span class="keyword">typename</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">result_of</span><span class="special">&lt;</span>
    <span class="identifier">phoenix</span><span class="special">::</span><span class="identifier">evaluator</span><span class="special">(</span>
        <span class="identifier">Expr</s