pan> <span>'a <a href="../module-type-FOLDABLE/index.html#type-t">t</a></span> := <span><span class="type-var">'a</span> <a href="index.html#type-t">t</a></span></code></span></summary><dl><dt class="spec type" id="type-t"><a href="#type-t" class="anchor"></a><code><span class="keyword">type</span> <span>'a t</span></code></dt></dl><dl><dt class="spec value" id="val-fold_left"><a href="#val-fold_left" class="anchor"></a><code><span class="keyword">val</span> fold_left : <span>(<span class="type-var">'a</spa