问题描述
如果我在 Prolog 中有一个列表，例如 X = [1, 2, 3, 4]，我如何将元素 5 添加到列表的末尾以使 X = [1, 2, 3, 4,5]?
If I have a list in Prolog such as X = [1, 2, 3, 4], how do I add the element 5 to the end of the list to have X = [1, 2, 3, 4, 5]?
append 函数需要两个列表，即 append(A,B,C) 将 A 和 B 连接到列表 C.
The append function needs two lists, ie append(A,B,C) to get A and B concatenated to the list C.
我可以用一个临时列表 Y = [1, 2, 3, 4] 和 Z = [5] 来做这个，然后做一个追加(Y，Z，X)，但我不喜欢有一个临时清单.
I can do this with a temporary list Y = [1, 2, 3, 4] and Z = [5], to then do an append(Y, Z, X), but I don't like having a temporary list.
通常的免责声明适用于此 - 这不是家庭作业，我只是在学习 Prolog.
The usual disclaimers apply here - this is not homework and I am just learning Prolog.
推荐答案
Prolog 中的变量只能赋值一次.只要 X 具有值 [1,2,3,4]，它就永远不会有另一个值.就像你提到的那样，一个临时变量和 append/3 是这样做的.
Variables in Prolog can only be assigned once. As soon as X has the value [1,2,3,4] it can never have another value. A temporary variable and append/3, like you mentioned, is the way to do it.
话虽如此，你可以做一个可能不推荐的技巧.如果 X = [1,2,3,4,Y] 那么你可以做 Y=5 并且 X 现在有你想要的值.我相信这种技术被称为差异列表.
Having said that, you can do one trick which probably isn't recommended. If X = [1,2,3,4,Y] then you can do Y=5 and X now has the value you want. I believe this technique is called a difference list.
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