an> <span class="keyword">sig</span> ... <span class="keyword">end</span></code></div><div class="spec module-type" id="module-type-FOLD_MAP"><a href="#module-type-FOLD_MAP" class="anchor"></a><code><span class="keyword">module</span> <span class="keyword">type</span> <a href="module-type-FOLD_MAP/index.html">FOLD_MAP</a> = <span class="keyword">sig</span> ... <span class="keyword">end</span></code></div><div class="spec module" id="module-Fold"><a href="#module-Fold" class="anchor"></a><code><span class="k