Question

我是Prolog的新手，我有一个问题。我有两个条款：

perform([X,Y], move(west),  [NX,Y]) :- NX is X - 1, !.
perform([X,Y], move(south), [X,NY]) :- NY is Y - 1, !.

X和Y是我的坐标。我想要的就是这样：

perform([X,Y], move(west), [NX,Y]):- NX is X - 1, !.
if NX == abs(Y)
perform([X,Y], move(west), [NX,Y]):- NX is X - 1, !.
else
perform([X,Y], move(south), [NX,NY]):- NY is Y - 1, !.

基本上移动（向西）并且如果我的X坐标是someValue move（向南）。

Answer 1

您可以尝试类似

的内容

perform([X,Y], move(west),  [NX,Y]) :- NX is X - 1, !.
perform([X,Y], move(south), [X,NY]) :- NY is Y - 1, !.

NX == abs(Y) -> perform([X,Y], move(west), [NX,Y]);
                perform([X,Y], move(south), [NX,NY]).

或

NX == abs(Y) -> NX is X - 1;
                NY is Y - 1.

Answer 2

有许多方法可以实现您需要的条件操作。

示例1 - 使用数学表达式进行的条件（不是最可读的条件）：

perform2([X,Y], move(west),  [NX,NY]) :-
    NX is X - 1,
    NY is Y - 1*0^(NX-abs(Y)),
    !.

示例2 - 使用运算符->/2和;/2生成的条件：

perform3([X,Y], move(west),  [NX,NY]) :-
    NX is X - 1,
    (    NX =:= abs(Y) -> NY is Y - 1; NY = Y ),
    !.

示例3 - 使用单独的条款进行的条件：

perform4([X,Y], move(west),  [NX,NY]) :-
    NX is X - 1,
    NX =:= abs(Y),
    NY is Y - 1,
    !.

perform4([X,Y], move(west),  [NX,Y]) :-
    NX is X - 1,
    NX =\= abs(Y),
    !.

对于所有上述谓词，输入和输出如下所示：

?- perform4([1,0], move(west), X).
X = [0, -1].

?- perform4([2,0], move(west), X).
X = [1, 0].

在特定时间后调用函数

2 个答案: