Prolog：如何验证用户输入？

Question

我是 Prolog 的新手，正在尝试实现教科书中的示例。我已经能够让示例正常工作（通过以前的 Stack Overflow 帖子的明确帮助！），但现在它要求我验证用户输入："Modify the given decision tree program, so that when the user responds to a question with an illegal answer, the system will ask him/her to reenter an answer which is among the specified choices."

在下面的程序中，对于婚姻状况，决策树中考虑的指定唯一选项是 "single" 或 "married." 如果您输入任何其他内容，目标是让您重新输入您的决定。

这对我不起作用。我的代码如下：

:-dynamic income/2.
:-dynamic marital_status/2.
:-dynamic mortgage/2.
:-dynamic age/2.

marital_status(joe,married).
income(joe,60000).
mortgage(joe,20000).
age(joe,45).

main(X,Z):-var(X), write('what is your name?'),read(X), invest(X,Z),!.
main(X,Z):-invest(X,Z),!.
ask_marital_status(X,Y):-marital_status(X,Y).
ask_marital_status(X,Y):-not(marital_status(X,Y)), write('what is your marital status: married or single?'), read(Y), nl, asserta(marital_status(X,Y)).
ask_marital_status(X,Y):-Y \=married, Y \=single, write('what is your marital status: married or single?'), read(Y), nl, asserta(marital_status(X,Y)).
%ask_marital_status(X,Y):-Y \= married; Y \= single, ask_marital_status(X,Y).
ask_income(X,Y):-income(X,Y).
ask_income(X,Y):-not(income(X,Y)),write('what is your annual income?'), nl, read(Y), asserta(income(X,Y)).
ask_mortgage(X,Z):-mortgage(X,Z).
ask_mortgage(X,Z):-not(mortgage(X,Z)), write('what is your mortgage?'), read(Z), nl, asserta(mortgage(X,Z)).
ask_age(X,A):-age(X,A).
ask_age(X,A):-not(age(X,A)), write('what is your age?'), read(A), nl, asserta(age(X,A)).

moderate_risk(X):-ask_marital_status(X,Y), Y=married, ask_income(X,I), I=<50000, ask_mortgage(X,Z), Z=<50000,!.
moderate_risk(X):-ask_marital_status(X,M), M=married, ask_income(X,I), I=<50000,!.
moderate_risk(X):-ask_marital_status(X,M), M=single, ask_income(X,I), I=<35000,!.
stable_risk(X):-ask_marital_status(X,M), M=married, ask_income(X,I), I=<50000, ask_mortgage(X,Z), Z>50000,!.
stable_risk(X):-ask_marital_status(X,M), M=single, ask_income(X,I), I>35000, ask_age(X,A), A>50, !.
high_risk(X):-ask_marital_status(X,M), M=single, ask_income(X,I), I>35000, ask_age(X,A), A=<50, !.

invest(X,oil):-stable_risk(X),!.
invest(X,telecommunications):-moderate_risk(X),!.
invest(X,computers):-high_risk(X),!.

第三个 "ask_martial_status" 是我目前试图让用户重新输入他们的决定，但它不起作用。我已经尝试使用 Prolog 的 AND 运算符 (,) 和它们的 or 运算符 (;) - 两者都没有区别（对于我放在 Y\= married 和 Y\=single 之间的内容）。当我输入错误的输入时，我只得到 "false" 返回。下面是一个例子：

?- main(X,Z).
what is your name?logan.
what is your marital status: married or single?|: widowed.

false.

注释掉的行（带有 %）是之前尝试让程序运行但也失败了。当我 Google 解决这个问题时，我很惊讶我无法找到一个快速的 YouTube 视频/文章来阅读。有人可以帮我吗？

Answer 1

您可以通过这种方式解决您的问题（相关预聚焦的片段）：

ask_marital_status(X,Y):-
    \+ marital_status(X,Y), 
    write('what is your marital status: married or single?'), 
    read(Y1),
    ( (Y1 == single ; Y1 == married) -> 
        Y = Y1,
        asserta(marital_status(X,Y)); 
        ask_marital_status(X,Y)
    ).

你可以用(Y1 = single ; Y1 = married)检查你读取的值（Y1）是single还是married（;表示或）。然后，如果是 (->)，则继续进行谓词的其余部分。否则，（在 asserta/1 旁边的 ; 之后）你调用 recursively marital_status/2.

编辑：感谢 Paulo Moura 的评论，=/2（统一）必须替换为 ==/2（平等），以使代码按预期运行。

Answer 2

读取和验证用户输入的传统方法是使用以下模板：

ask(Data) :-
    repeat,
        write(Prompt),
        read(Data),
    valid(Data),
    !.

将此模板应用于您的案例，我们可以编写：

ask_marital_status(Status) :-
    repeat,
        write('What is your marital status (married or single)?'),
        read(Status)
    (   Status == married
    ;   Status == single
    ),
    !.

作为一般规则，最佳做法是将询问用户输入与处理输入（在您的情况下断言事实）分开。

高级解决方案将使用消息打印和问题询问机制进行用户交互（参见 https://logtalk.org/2019/11/14/abstracting-user-interaction.html）。但这是一个更高级的话题。

Prolog：如何验证用户输入？

Prolog: How to Verify User Input?

input

prolog

verify