ljs-type">Number</span> = <span class="hljs-keyword">ref</span> <span class="hljs-keyword">object</span>
      height: <span class="hljs-built_in">int</span>
      <span class="hljs-keyword">case</span> isPair: <span class="hljs-built_in">bool</span>
      <span class="hljs-keyword">of</span> <span class="hljs-literal">true</span>:
          left, right: <span class="hljs-type">Number</span>

      <span class="hljs-keyword">of</span> <span class="hljs-literal">false</span>:
          value: <span class="hl