我正在努力完成底部的练习我发现自己对第三点完全困惑。
我们获得以下旅游信息知识库:
byCar(auckland, hamilton).
byCar(hamilton, raglan).
byCar(valmont, saarbruecken).
byCar(valmont, metz).
byTrain(metz, frankfurt).
byTrain(saarbruecken, frankfurt).
byTrain(metz, paris).
byTrain(saarbruecken, paris).
byPlane(frankfurt, bangkok).
byPlane(frankfurt, singapore).
byPlane(paris, losAngeles).
byPlane(bangkok, auckland).
byPlane(singapore, auckland).
byPlane(losAngeles, auckland).
了解是否可以在两个城市之间旅行很简单。我刚刚这样做了:
connected(X, Y) :- byCar(X, Y); byTrain(X, Y); byPlane(X, Y).
travel(X, Y) :- connected(X, Y).
travel(X, Z) :- connected(Y, Z), travel(X, Y).
然而,当我必须实际将路径与变量统一时,我完全困惑了!
我写了这个:
connected(X, Y) :- byCar(X, Y); byTrain(X, Y); byPlane(X, Y).
connected(Y, Z, Out) :- connected(Y, Z).
travel(X, Y, Out) :- connected(X, Y).
travel(A, Z, Out) :- connected(Y, Z),travel(A, Y, connected(Y, Z, Out)).
并打电话给travel(valmont, losAngeles,X).
除了末尾的匿名变量之外,在跟踪过程中的某个点会显示正确的路径:
travel(valmont, metz, connected(metz, paris, connected(paris, losAngeles, _17)))
但我实际上不知道如何将其与变量统一X
!
我实在无法全神贯注于此。谁能给我一个提示,把我推向正确的方向?我只是缺少一个终止条件还是什么?
Edit:
我现在有:
connected(X,Y) :- byCar(X,Y);byTrain(X,Y);byPlane(X,Y).
go(X,Y) :- connected(X,Y).
travel(X,Y,go(X,Y)) :- connected(X,Y).
travel(A,Z,Path) :- travel(Y,Z,Path),go(A,Y,Path).
go(A,Y,Path) :- travel(A,Y,Path).
但它会像这样卡住:
4 4 Exit: byPlane(paris,losAngeles) ?
3 3 Exit: connected(paris,losAngeles) ?
2 2 Exit: travel(paris,losAngeles,go(paris,losAngeles)) ?
5 2 Call: go(metz,paris,go(paris,losAngeles)) ?
6 3 Call: travel(metz,paris,go(paris,losAngeles)) ?
7 4 Call: travel(_217,paris,go(paris,losAngeles)) ?
8 5 Call: travel(_242,paris,go(paris,losAngeles)) ?
9 6 Call: travel(_267,paris,go(paris,losAngeles)) ?
10 7 Call: travel(_292,paris,go(paris,losAngeles)) ?
我已经玩过它了,但我无法让它构建整个go(a,b,go(b,c))
etc...