I find this easier to understand with a visualization. Here I’m using purple ovals for calls to node, green rectangles for calls to cons, black ovals for calls to empty and black rectangles for calls to nil:
Creating custom commands
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这个项目从去年上半年就开始酝酿,内部被列为「最高优先级绝密项目」。。关于这个话题,谷歌提供了深入分析
if !groups.has(s.grade) {