Prolog中列表的串联

问题描述

有人可以帮我找到这些规则中的错误吗?

Can someone help me find the error in these rules?

concat([], List, List).
concat([Head|[]], List, [Head|List]).
concat([Head|Tail], List, Concat) :- concat(Tail, List, C), concat(Head, C, Concat).

尝试串联两个列表失败:

Trying to concatenate two lists fails:

| ?- concat([1,2], [4,7,0], What).

no

推荐答案

要修改代码，按预期的方式，您只需在上次调用中将Head转换为[Head]即可，最后一句.问题是您仅使用Head作为第一个参数(而不是列表)来调用谓词.

To fix your code, the way you intended it, you just need to transform Head into [Head] in your last call to concat/3 in your last clause. The problem was that you called your predicate with Head only as first argument, which is not a list.

不过，这里有几个注意事项:

Though, here are several notes :

• [Head|[]]等同于[Head]
• 您的算法的复杂度很差，n！我相信.
• 在第二个子句之后未插入剪切，您可以通过调用长度为1的列表的第三个子句来生成无限选择点(因此调用了第二个子句，然后再遍历第三个子句，依此类推. .无限循环).

• [Head|[]] is equivalent to [Head]
• your algorithm has a poor complexity, n! I believe.
• with no cut inserted after your second clause, you generate infinite choice points through the call of your third clause with a list of length 1 (that hence calls your second clause, that then is ran through your third clause, etc... infinite loop).

这是SWI-pl的版本，以提示您迈向良好的序言递归:

Here is SWI-pl's version, to hint you towards good prolog recursion :

append([], List, List).
append([Head|Tail], List, [Head|Rest]) :-
    append(Tail, List, Rest).

您可以在这里或在立即学习Prolog中找到其他资源！

You can find other resources on recent posts here or in Learn Prolog Now! tutorial if you want to learn how to use recursion properly.

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