> <span><span class="label">f</span>:<span>(<span><span class="type-var">'acc</span> <span class="arrow">&#45;&gt;</span></span> <span><span>(<a href="#type-key">key</a> * <a href="#type-value">value</a>)</span> <span class="arrow">&#45;&gt;</span></span> <span class="type-var">'acc</span>)</span> <span class="arrow">&#45;&gt;</span></span> <span class="type-var">'acc</span></span></code></div></div><div class="odoc-spec"><div class="spec value anchored" id="val-fold_map"><a href="#val-fold_map" class="anch