><a href="../Tree/index.html#type-re">Tree.re</a> <span class="arrow">&#45;&gt;</span></span> bool</span></code></div><div class="spec-doc"><p><code>is_nullable r</code></p><ul class="at-tags"><li class="returns"><span class="at-tag">returns</span> <p>true iff Epsilon is accepted by the RE <code>r</code></p></li></ul></div></div><div class="odoc-spec"><div class="spec value anchored" id="val-derivative"><a href="#val-derivative" class="anchor"></a><code><span><span class="keyword">val</span> derivative : <s