在 Prolog 中寻找最年长的人 [英] Finding the oldest person in Prolog

问题描述

根据一些事实，我必须找到使用 Prolog 的最年长的人.例如:

Based on some facts, I have to find the oldest person using Prolog. For example:

age(john, 10).
age(mary, 15).
age(rose, 75).
age(jack, 49).
age(carl, 17).
age(lucy, 66).

控制台输出应该是:

?- oldest(rose).
True.

?- oldest(X).
X = rose.

我的代码如下，但不起作用:

My code is as follows, but it's not working:

oldest(P) :- age(P, X) , age(_, Y) , X >= Y.

我找不到错误，但我想这与回溯有关.有人可以帮我吗?我是 Prolog 的新手.

I can't find the error, but I guess it's something related to backtrack. Could someone help me, please? I'm new to Prolog.

推荐答案

正确的应该是

oldest(P) :- age(P, X) , \+ (age(_, Y) , Y > X).

当然，收益率上升了...

that yields rose, of course...

(\+)/1 读作 not(Goal)，意思是如果目标没有解决方案就失败".

(\+)/1 read as not(Goal), and means 'fail if there are no solutions to Goal'.

编辑在 SWI-Prolog，库(aggregate) 可以做到这一点，还有更多......

edit in SWI-Prolog, library(aggregate) can do this, and much more...

oldest(P) :- aggregate(max(A,Pers), age(Pers,A), max(_,P)).

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