ld_map"><a href="#val-fold_map" class="anchor"></a><code><span><span class="keyword">val</span> fold_map : <span><span><span class="type-var">'a</span> <a href="#type-t">t</a></span> <span class="arrow">&#45;&gt;</span></span> <span><span class="label">init</span>:<span class="type-var">'b</span> <span class="arrow">&#45;&gt;</span></span> <span><span class="label">f</span>:<span>(<span><span class="type-var">'b</span> <span class="arrow">&#45;&gt;</span></span> <span><span class="type-var">'a</span> <span 