span class="keyword">val</span> merge : <span>(<a href="index.html#type-key">key</a> <span>&#45;&gt;</span> <span><a href="index.html#type-value">value</a> option</span> <span>&#45;&gt;</span> <span><a href="index.html#type-value">value</a> option</span> <span>&#45;&gt;</span> <span><a href="index.html#type-value">value</a> option</span>)</span> <span>&#45;&gt;</span> <a href="index.html#type-t">t</a> <span>&#45;&gt;</span> <a href="index.html#type-t">t</a> <span>&#45;&gt;</span> <a href="index.html#type-t"