Prolog 错误参数未实例化

如何解决Prolog 错误参数未实例化

运行此代码时：

signcheck(Sign1,Sign2):-(Sign1==clubs,Sign2==hearts);(Sign1==clubs,Sign2==spades)
                            ;(Sign1==clubs,Sign2==diamonds);(Sign1==hearts,Sign2==spades)
                            ;(Sign1==hearts,Sign2==diamonds);(Sign1==spades,Sign2==diamonds).
    lowercard(card(Num1,Sign1),card(Num2,_),card(Num1,Sign1)):- Num1<Num2.
    lowercard(card(Num1,Sign2),Sign1)):- Num1==Num2,signcheck(Sign1,Sign2).
    lowercard(card(Num1,Sign2)):- Num1==Num2,signcheck(Sign2,Sign1).
    lowercard(card(Num1,Sign2)):- Num1>Num2.
    lowest([card(X,Y)],card(X,Y)).
    lowest([X|XS],Z):- lowercard(X,Y,Z),lowest(XS,Y).

运行查询时：

lowest([card(5,hearts),card(4,diamonds)],X)

我收到此错误消息：

Arguments are not sufficiently instantiated
In:
   [3] 5<_1600
   [2] lowercard(card(5,card(_1668,_1670),card(5,hearts)) at  line 4
   [1] lowest([card(5,...],hearts)) at  line 8

为什么会出现这种情况？

解决方法

除非所有参数都被实例化，否则无法计算算术运算（例如 <）。如果您的情况，右侧参数（Num2，看起来像）尚未实例化。