在 Prolog 规则中使用事实列表 [英] Using a list from a fact within Prolog rules

问题描述

我目前正在编写一个铁路线程序，但在使用来自事实的列表时遇到了一点麻烦.我对 Prolog 很陌生，到目前为止，我已经写了以下事实和规则:

I am currently writing a rail line program but am having a little trouble using lists that come from facts. I am quite new to Prolog and so far have written the following facts and rules:

location(euston, [northernLine]).
location(warrenStreet, [victoriaLine, northernLine]).
location(warwickAvenue, [bakerlooLine]).
location(paddington, [bakerlooLine]).

hasCommonLine(Location1, Location2, Line) :-
    location(Location1, Line),
    location(Location2, Line).

这个想法是让规则返回两个位置共有的行的名称.如果我尝试 hasCommonLine(warwickAvenue,paddington,Line). 这会有效，但是如果我尝试 hasCommonLine(euston,warrenStreet,Line)..

The idea is for the rule to return the name of the line(s) that the two locations have in common. This works if I try hasCommonLine(warwickAvenue,paddington,Line). , however it returns false if I try hasCommonLine(euston,warrenStreet,Line)..

我怀疑这是因为规则只检查列表的第一个元素，因此只比较 [northernLine] 和 [victoriaLine] 而不是检查列表中的每个元素列表.任何指导来实现这一点将不胜感激！

I suspect this is because the rule only checks the first element of the lists, therefore only compares [northernLine] and [victoriaLine] rather than checking every element in the list. Any guidance to accomplish this would be much appreciated!

推荐答案

您可以检查 Line 是否是两个列表的成员:

You can check if Line is a member of both lists:

 hasCommonLine(Location1, Location2, Line) :-
     location(Location1, Lines1),
     location(Location2, Lines2),
     member(Line, Lines1),
     member(Line, Lines2).

然后，如果您需要找到两个位置之间的所有公共线，您只需调用

Then, if you need to find all the lines common between two locations, you would simply call

 ?- findall(X, hasCommonLine(euston, warrenStreet, X), Y).
 Y = [northernLine].

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