序言树遍历 [英] Prolog Tree Traversal

问题描述

美好的一天，

我正在尝试编写一个Prolog程序，该程序给出了一个带有a的函子的树：

I am trying to write a Prolog program that given a tree with a functor of a:

start(a(f,2,9), X).

我希望它对内部的任何值求平方，从而产生：

I want it to square any values inside so that it yields:

X = a(f,4,81).

我有一些代码可以对列表中的数字进行平方运算。
这是到目前为止的内容：

I have code that squares numbers in a list already that works. Here's what I have so far:

start([],[]).
start(Tree, []) :- Tree =.. [P|C], write(P), nl, write(C), nl, squareMe([P|C], []).
squareMe([X|T], [Y|Result]) :-   % I think the problem is here
    atom(X),
    Y=X,
    squareMe(T, Result).
squareMe([X|T], [Y|Result]) :- 
    number(X),
    Y is X * X,
    squareMe(T, Result).
squareMe([], []).

当代码写P和C时，我确实通过UNIV运算符获得了正确的值，但是

when the code writes P and C, I do get the correct values via the UNIV operator, but it seems to be failing inside squareMe.

当我调用squareMe（[P | C]，[]）时，我的理解是P = a和C = [f， 2、9]。那么atom（a）不应该是真的吗？似乎并非如此，我不确定为什么吗？

When I invoke squareMe([P|C], []), my understanding is the P = a and C = [f, 2, 9]. So shouldn't atom(a) be true? It doesn't appear to be the case and I'm not sure why?

我已经尝试过使用trace / notrace跟踪我的路径，但是肯定会很高兴看到传递给squareMe的值。那可能吗？我正在使用SWI-Prolog。

I've tried using trace/notrace to track my path, but it would sure be nice to see the values that were passed into squareMe. Is that possible? I'm using SWI-Prolog.

TIA，
子孙

TIA, coson

推荐答案

这是答案，而不是评论，只是因为它太长；我还是不完全理解您的问题。

This is an answer instead of a comment only because it is too long; I don't fully understand your question though.

要获得您在顶部显示的查询的解决方案，只需编写：

To get the solution to the query you show at the top, it would be enough to write:

start(a(f, X, Y), a(f, XX, YY)) :-
    XX is X*X,
    YY is Y*Y.

就是这样：

?- start(a(f, 2, 9), X).
X = a(f, 4, 81).

这太简单了，更重要的是，我在这里看不到任何树形结构，这就是为什么我确定我误解了这个问题。按照您显示的代码，我肯定会遇到麻烦。您应该编辑问题来解释：

This is way too easy, and more importantly, I don't see any tree structure here, which is why I am certain I am misunderstanding the question. I definitely have trouble following the code you have shown. You should edit your question to explain:

• 您要遍历的树结构在哪里？


• 您是否在使用列表，平面术语，嵌套术语（一棵树？）


• 您的谓词必须同时使用两种方法，所以，您应该能够问： ？-start（X，Y）。。例如

• where is the tree structure you are traversing?
• are you using lists, flat terms, nested terms (a tree?)
• does your predicate have to work both ways, so, should you be able to ask: ?- start(X, Y). for example.

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