几何类比，为什么我得不到更多答案？(Geometry analogy, why don't I get more answer?)

几何类比，为什么我得不到更多答案？(Geometry analogy, why don't I get more answer?)

这是我的prolog代码：

figure(1, middle(circle, circle)). figure(2, top_left(circle, circle)). figure(3, bottom_right(circle, circle)). figure(4, middle(square, square)). figure(5, top_left(square, square)). figure(6, top_right(square, square)). figure(7, bottom_right(square, square)). figure(8, bottom_left(square, square)). relate(F1, F2, Relation) :- ( figure(F1, middle(X, Y)), figure(F2, middle(Y, X)), F1 \== F2 -> Relation = invert ; figure(F1, middle(X, X)), figure(F2, middle(Y, Y)), F1 \== F2 -> Relation = same_in_out ; figure(F1, top_left(X, X)), figure(F2, bottom_right(Y, Y)), F1 \== F2 -> Relation = opposite ; figure(F1, top_right(X, X)), figure(F2, bottom_left(Y, Y)), F1 \== F2 -> Relation = opposite ; relate(F2, F1, Relation) ). analogy((F1, F2), (F3, X)) :- relate(F1, F2, Relation), relate(F3, X, Relation).

代表这一套

这是一个简单的执行：

| ?- relate(2, X, Y). X = 3 Y = opposite; no | ?- relate(2, 7, X). X = opposite; no

我的问题是，为什么我没有X = 7，Y =相反，当我确实相关（2，X，Y）？

谢谢。

Here is my prolog code :

figure(1, middle(circle, circle)). figure(2, top_left(circle, circle)). figure(3, bottom_right(circle, circle)). figure(4, middle(square, square)). figure(5, top_left(square, square)). figure(6, top_right(square, square)). figure(7, bottom_right(square, square)). figure(8, bottom_left(square, square)). relate(F1, F2, Relation) :- ( figure(F1, middle(X, Y)), figure(F2, middle(Y, X)), F1 \== F2 -> Relation = invert ; figure(F1, middle(X, X)), figure(F2, middle(Y, Y)), F1 \== F2 -> Relation = same_in_out ; figure(F1, top_left(X, X)), figure(F2, bottom_right(Y, Y)), F1 \== F2 -> Relation = opposite ; figure(F1, top_right(X, X)), figure(F2, bottom_left(Y, Y)), F1 \== F2 -> Relation = opposite ; relate(F2, F1, Relation) ). analogy((F1, F2), (F3, X)) :- relate(F1, F2, Relation), relate(F3, X, Relation).

Which represent this set

And here is a simple execution :

| ?- relate(2, X, Y). X = 3 Y = opposite; no | ?- relate(2, 7, X). X = opposite; no

And my question is, why I don't have X = 7, Y = opposite, when I do relate(2, X, Y) ?

Thank you.

最满意答案

因为你使用if-then-else，而Prolog不会回溯这样的结构：

?- (member(X, [1,2,3]) -> Y = hello ; Y = goodbye). X = 1, Y = hello. ?-

If-then-else真正意味着有效的确定性计算。 如果你想要非确定性/回溯，你应该使用普通的连词，析取和事实列表来重写你的谓词：

relate(F1, F2, Relation) :- figure(F1, Fig1), figure(F2, Fig2), relate_(Fig1, Fig2, Relation), F1 \== F2. relate_(middle(X, Y), middle(Y, X), invert). % etc.

Because you use if-then-else, and Prolog won't backtrack out of such a construct:

?- (member(X, [1,2,3]) -> Y = hello ; Y = goodbye). X = 1, Y = hello. ?-

If-then-else is really meant for efficient deterministic computation. You should rewrite your predicate using ordinary conjunction, disjunction and listings of facts if you want non-determinism/backtracking:

relate(F1, F2, Relation) :- figure(F1, Fig1), figure(F2, Fig2), relate_(Fig1, Fig2, Relation), F1 \== F2. relate_(middle(X, Y), middle(Y, X), invert). % etc.