prolog 的独特结果 [英] unique results from prolog

问题描述

是否有一种简单的方法可以让 prolog 中的查询只返回每个结果一次?

Is there a easy way to make a query in prolog only return each result once?

例如我正在尝试类似的东西:

for instance I'm trying something like:

deadly(Xn) :- scary(X), Xn is X - 1, Xp is X + 1, not(safe(Xn)), safe(Xp).
deadly(Xp) :- scary(X), Xn is X - 1, Xp is X + 1, not(safe(Xp)), safe(Xn).

deadly(X).

并得到

X = 5

X = 5

X = 5

X = 5

....

对我没用.

推荐答案

您可以做的一件事是将 setof/3 应用于生成解决方案的谓词.但请注意，setof/3 是通过将 sort/2 应用于 bagof/3 传递的结果来实现的(至少在SWI-序言).因此，如果您的解决方案生成器永远运行下去，那么 setof/3 将永远不会被应用...

One thing that you can do is to apply setof/3 to the predicate that generates the solutions. But note that setof/3 is implemented by applying sort/2 to the result delivered by bagof/3 (at least this is the case in SWI-Prolog). So, if your solution generator goes on forever, then setof/3 will never be applied...

所以我想说的是尝试编程以免生成重复项，即在有意义的地方使用剪切 (!).

So I would say that try to program so that duplicates are not generated, i.e. by using the cut (!) where it makes sense.

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