Function env_var</span></h2>
<p>boost::proto::env_var &#8212; 
          For fetching the value from a transform environment corresponding to the
          specified <code class="computeroutput">Key</code>.
        </p>
</div>
<h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2>
<div xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv"><pre class="synopsis"><span class="comment">// In header: &lt;<a class="link