al-merge" class="anchor"></a><code><span><span class="keyword">val</span> merge : 
  <span><span>(<span><a href="#type-key">key</a> <span class="arrow">&#45;&gt;</span></span> <span><span><a href="#type-value">value</a> option</span> <span class="arrow">&#45;&gt;</span></span> <span><span><a href="#type-value">value</a> option</span> <span class="arrow">&#45;&gt;</span></span> <span><a href="#type-value">value</a> option</span>)</span> <span class="arrow">&#45;&gt;</span></span>
  <span><a href="#type-t">t<