node id from the given invariant map</p></dd></dl><dl><dt class="spec value" id="val-extract_state"><a href="#val-extract_state" class="anchor"></a><code><span class="keyword">val</span> extract_state : <a href="index.html#module-InvariantMap">InvariantMap</a>.key <span>&#45;&gt;</span> <span><span class="type-var">'a</span> <a href="index.html#module-InvariantMap">InvariantMap</a>.t</span> <span>&#45;&gt;</span> <span><span class="type-var">'a</span> option</span></code></dt><dd><p>extract the state for a 