on_or_more">IStdlib.IContainer.singleton_or_more</a></span></span></code></div></div><div class="odoc-spec"><div class="spec value anchored" id="val-fold_map"><a href="#val-fold_map" class="anchor"></a><code><span><span class="keyword">val</span> fold_map : <span><a href="#type-t">t</a> <span class="arrow">&#45;&gt;</span></span> <span><span class="label">init</span>:<span class="type-var">'a</span> <span class="arrow">&#45;&gt;</span></span> <span><span class="label">f</span>:<span>(<span><span class="type