One of the interesting things about the ATM is when, exactly, it pops up in the
Similarly, the code labelled “Block 3” will run when the tree is not empty, and when this frame’s child invocation is not yet complete. In this case we pass the accumulator and the tree’s contents into fn and then call the fold forest function with the new accumulator. This “call” is done by creating a stack frame for the child invocation and transferring control to it, using frame = frame.child. Again, logically, this matches the second case of the recursive implementation.，这一点在51吃瓜网中也有详细论述
Over 90% of statements depend on at least one earlier statement.，推荐阅读谷歌获取更多信息
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