反转Prolog中的列表 [英] Reversing a List in Prolog

问题描述

我已经完成了我的编程课的家庭作业.我本该创建一个Prolog程序来反转一个列表.但是，我在理解其确切工作原理方面遇到了麻烦.

I have finished a homework assignment for my programming class. I was supposed to create a Prolog program that reverses a list. I, however, am having trouble understanding why exactly it works.

%1. reverse a list
%[a,b,c]->[c,b,a]

%reverse(list, rev_List).
reverse([],[]).  %reverse of empty is empty - base case
reverse([H|T], RevList):-
    reverse(T, RevT), conc(RevT, [H], RevList).  %concatenation

在这种情况下RevT到底是什么?我知道它应该代表T或给定列表的其余部分的倒数，但是我没有看到它有什么价值，因为我没有将其分配给任何东西.它是否与RevList具有相同的目的，但又适用于每个递归调用?

What exactly is RevT in this case? I know it is supposed to represent the reverse of T or the rest of the given list, but I don't see how it could have any value as I haven't assigned it to anything. Does it just serve the same purpose as RevList but for each recursive call?

此外，为什么我必须在我的conc()函数调用中使用[H]而不是仅使用H? H不是指列表的头(例如:[H])吗?还是只引用列表顶部的项目(仅H)?

Also, why do I have to use [H] instead of just H in my conc() function call? Doesn't H refer to the head of the list (ex: [H])? Or does it just refer to the item at the head of the list (just H)?

请帮我解决这个问题.我正在努力理解这种编程背后的逻辑.

Please help clear this up for me. I am struggling to understand the logic behind this type of programming.

推荐答案

您的解决方案说明: 如果我们反转空白列表，我们将获得空白列表. 如果反转列表[H | T]，则最终得到的是通过反转T并与[H]串联而获得的列表. 要查看递归子句是正确的，请考虑列表[a，b，c，d].如果我们反转此列表的末尾，则会得到[d，c，b].将其与[a]结合会产生[d，c，b，a]，这与[a，b，c，d]的相反方向

Your solution explained: If we reverse the empty list, we obtain the empty list. If we reverse the list [H|T] , we end up with the list obtained by reversing T and concatenating with [H] . To see that the recursive clause is correct, consider the list [a,b,c,d] . If we reverse the tail of this list we obtain [d,c,b] . Concatenating this with [a] yields [d,c,b,a] , which is the reverse of [a,b,c,d]

另一种反向解决方案:

 reverse([],Z,Z).

 reverse([H|T],Z,Acc) :- reverse(T,Z,[H|Acc]).

致电:

?- reverse([a,b,c],X,[]).

有关更多信息，请阅读: http://www. Learnprolognow.org/lpnpage.php?pagetype=html&pageid=lpn-htmlse25

For further information please read: http://www.learnprolognow.org/lpnpage.php?pagetype=html&pageid=lpn-htmlse25

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