Question

大家好，这是我第一次来这里:)！

我有以下Prolog定义集，唯一不起作用的是Subclass。任何人都可以帮助我弄清楚为什么这不是:(

    % definitions of classes in our system 
    class(object). 
    class(animal). 
    class(cat). 
    class(dog). 
    class(dachshund). 
    class(toy). 
class(ball). 
class(post). 

% definitions of interfaces 
interface(iwoof). 
interface(imeow). 

% definitions of class inheritance 
inherits(animal,object). 
inherits(cat,animal). 
inherits(dog,animal). 
inherits(dachshund, dog). 
inherits(toy,object). 
inherits(ball,object). 
inherits(post,object). 
inherits(ball,toy).
inherits(post,toy).

% definitions of interface implementation 
implements(cat,imeow). 
implements(dog,iwoof). 

% definitions of objects (instances of classes) 
instance(fluffy,cat). 
instance(fido,dog). 
instance(rex,dog). 
instance(schnitzel,dachshund). 
instance(superscratch,post). 
instance(bouncyball,ball). 
instance(tennisball,ball). 

% definitions of behavior 
playswith(cat,post). 
playswith(dog,ball). 

% definitions of superclasses 
superclass(C,D) :- inherits(C,D). 
superclass(D,C) :- inherits(D,X), superclass(X,C). 

% definitions of subclasses 
subclass(C,D) :- superclass(X,D), inherits(C,X).

我需要的输出是

?- subclass(toy,X).
X = ball ;
X = post ;
false.

但是我得到了

假。

这是追踪。

?- trace, subclass(toy,X).
   Call: (7) subclass(toy, _G246) ? creep
   Call: (8) inherits(toy, _G366) ? creep
   Exit: (8) inherits(toy, object) ? creep
   Call: (8) superclass(object, _G246) ? creep
   Call: (9) inherits(object, _G246) ? creep
   Fail: (9) inherits(object, _G246) ? creep
   Redo: (8) superclass(object, _G246) ? creep
   Call: (9) inherits(object, _G366) ? creep
   Fail: (9) inherits(object, _G366) ? creep
   Fail: (8) superclass(object, _G246) ? creep
   Fail: (7) subclass(toy, _G246) ? creep
false.

Answer 1

如果您阅读了跟踪信息，则会看到最终问题：object没有继承，或者没有inherits(object, Anything).形式的事实。但这可能不是你的意思！

对我而言，似乎只是说：

subclass(A, B) :-
    superclass(B, A).

在你的情况下，

应该足够了。

Answer 2

Logtalk中的另一种实现（您可以将大多数Prolog系统作为后端编译器运行）：

:- object(metaclass,
    imports(class_hierarchy),   % from the standard library
    instantiates(metaclass)).   % make metaclass its own metaclass

:- end_object.


:- object(object,
    instantiates(metaclass)).

:- end_object.


:- object(animal,
    instantiates(metaclass),
    specializes(object)).

    :- public(playswith/1).

:- end_object.


:- protocol(imeow).

    :- public(imeow/0).

:- end_protocol.


:- protocol(iwoof).

    :- public(iwoof/0).

:- end_protocol.


:- object(cat,
    implements(imeow),
    instantiates(metaclass),
    specializes(animal)).

    imeow.
    playswith(post). 

:- end_object.


:- object(dog,
    implements(iwoof),
    instantiates(metaclass),
    specializes(animal)).

    iwoof.
    playswith(ball).

:- end_object.


:- object(dachshund,
    instantiates(metaclass),
    specializes(dog)).

:- end_object.


:- object(toy,
    instantiates(metaclass),
    specializes(object)).

:- end_object.


:- object(ball,
    instantiates(metaclass),
    specializes(toy)).

:- end_object.


:- object(post,
    instantiates(metaclass),
    specializes(toy)).

:- end_object.


:- object(fluffy,
    instantiates(cat)).

:- end_object.


:- object(fido,
    instantiates(dog)).

:- end_object.


:- object(rex,
    instantiates(dog)).

:- end_object.


:- object(schnitzel,
    instantiates(dachshund)).

:- end_object.


:- object(superscratch,
    instantiates(post)).

:- end_object.


:- object(bouncyball,
    instantiates(ball)).

:- end_object.


:- object(tennisball,
    instantiates(ball)).

:- end_object.

来自您帖子的示例查询：

?- toy::subclass(Subclass).
Subclass = ball ;
Subclass = post.

当然，在此解决方案中，您的任务主要是简化为指定层次结构和接口。通过自己实施继承来获得学习奖励。

如何在Prolog中编写子类语句？

2 个答案: