e></dt><dt class="spec type" id="type-union"><a href="#type-union" class="anchor"></a><code><span class="keyword">type</span> <span>'a union</span></code><code> = <span><span>(<span class="type-var">'a</span>, <span>[ `Union ]</span>)</span> <a href="index.html#type-structured">structured</a></span></code></dt><dt class="spec type" id="type-field"><a href="#type-field" class="anchor"></a><code><span class="keyword">type</span> <span>('a, 't) field</span></code><code> = <span><span>(<span class="type-var">'