prolog 子句定义的最大值 [英] Max out of values defined by prolog clauses

问题描述

我知道如何遍历 Prolog 中的列表以找到最大值，但是如果每件事都是一个单独的子句怎么办?例如，如果我有一群猫科动物和它们的年龄，我将如何找到最古老的小猫?

I know how to iterate over lists in Prolog to find the maximum, but what if each thing is a separate clause? For example if I had a bunch of felines and their ages, how would I find the oldest kitty?

cat(sassy, 5).
cat(misty, 3).
cat(princess, 2).

我的第一个想法是嗯，最老的猫是没有更老的猫".但我不能很好地翻译成序言.

My first thought was "hmm, the oldest cat is the one for which no older exists". But I couldn't really translate that well to prolog.

oldest(X) :- cat(X, AgeX), cat(Y, AgeY), X = Y, + AgeX < AgeY, print(Y).

这仍然错误地匹配misty".这样做的正确方法是什么?有什么方法可以更直接地迭代年龄以选择最大值?

This still errorenously matches "misty". What's the proper way to do this? Is there some way to more directly just iterate over the ages to choose max?

推荐答案

如果猫是猫并且没有比它大的猫，那么它就是最老的猫.让我们把它写在 Prolog 中:

A cat is the oldest if it's a cat and there is not a cat older than it. Let's write that in Prolog:

oldest(X):- cat(X, _), not( thereAreOlders(X)), !.
thereAreOlders(X):- cat(X, N), cat(C, M), C=X, M > N.

如果您咨询:

?- oldest(X).
X = sassy.

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