:#66d9ef">CartItem</span><span style="color:#f92672">]</span> <span style="color:#66d9ef">=</span> <span style="color:#a6e22e">Seq</span><span style="color:#f92672">.</span>empty<span style="color:#f92672">)</span><span style="color:#66d9ef">:</span>
  <span style="color:#66d9ef">def</span> <span style="color:#66d9ef">add</span><span style="color:#f92672">(</span><span style="color:#66d9ef">item:</span> <span style="color:#66d9ef">CartItem</span><span style="color:#f92672">)</span><span style="color:#66d9ef