需要帮助来理解用于追加列表元素的序言方法 [英] Require help understanding a prolog method for appending list elements
问题描述
append([],Xs,Xs).
append([Head|Tail],List2,[Head|Tail2]):-
append(Tail,List2,Tail2).
上部的append方法将前两个参数槽中的元素添加到第三个param变量中.
The upper append method adds elements from first two parameter slots to the third param variable.
?-append([2,1], [3,4], X).
?-X=[2,1,3,4]
我逐步看到它的方式是(这可能是错误的)->
The way i see it in steps is (which is propably wrong) ->
- append(2 | [1]，[3,4]，2 | X)
-
追加([1]，[3,4]，X)
- append(2 | [1], [3,4], 2 | X)
append([1], [3,4], X)
append(1 | []，[3,4]，1 | X)
append(1 | [], [3,4], 1 | X)
就是这样.我无法确定如何将元素添加到一起，这就是我可以使用的帮助-对这种方法的工作原理进行了清晰的解释.我只是不明白[2,1]数组是如何添加到最终结果中的.
And that's it. I can't wrap my head around how it adds together the elements and that's what i could use help with - a clear explanation on how this method works. I just don't understand how the [2,1] array gets added to the final result.
推荐答案
如果在跟踪中将其重命名，则递归中的X与原始调用中的X不相同. >
the X in the recursion is not the same X as in the original call if you rename it in the trace you'll see
append(2 | [1], [3,4], 2 | X1) -- X = [2|X1]
append([1], [3,4], X1)
append(1 | [], [3,4], 1 | X2) -- X1 = [1|X2]
append ([], [3,4], [3,4]) -- X2 = [3,4]
如此X1 = [1,3,4]和X = [2,1,3,4]
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