the parameter of closure 闭合度参数
The second parameter is a function closure.
第二个参数是一个函数闭包。
It defines a closure called recurse that can be called with only one parameter rather than two.
它定义了一个名为recurse的闭包，能够只使用一个参数来调用它，而不是两个。
Because it is a Seq, it has a foreach method that takes a closure as a parameter.
因为它是一个Seq，它具有一个foreach方法，并将一个闭包作为参数。
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