你需要声明枚举函数之前，在全球范围（即。

You need to declare your enum before any of your functions, in the global scope (ie. outside of any function).

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zippers的枚举函数允许您按照深度优先的顺序遍历整个树，如图11所示。

A zipper's enumeration functions allow you to traverse the entire tree in depth-first order, as shown in Figure 11.

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这些节点代表了具体的标识符，如函数名称、变量及枚举类型。

These represent specific identifiers, such as the names of functions, variables, and enumerated types.

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