ate transform_impl">proto::transform_impl</a><span class="special">&lt;</span> <span class="identifier">Expr</span><span class="special">,</span> <span class="identifier">State</span><span class="special">,</span> <span class="identifier">Data</span> <span class="special">&gt;</span> <span class="special">{</span>
  <span class="comment">// types</span>
  <span class="keyword">typedef</span> <span class="identifier">State</span> <a name="boost.proto._state.impl.result_type"></a><span class="identifier">resu