不带else的Prolog if语句

我以前也看到过类似的帖子，但我似乎还是被卡住了。我当前的if语句，即使失败，也会输出“if true”代码。所以我想问，如果条件变为false，我不想做任何其他事情，那么正确的语法是什么

我的失败代码：

(Disease == malaria
        ->  (patient_age(y)
            ->  writeln('Since patient is young, likelihood of malaria increases.')
            ;   true)
        ;
Disease == tuberculosis
        ->  (patient_age(e)
            ->  writeln('Since patient is old, likelihood of tuberculosis increases.')
            ;   true)
).

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发生的情况是，即使patient_age（）为false，writeln（）语句仍会执行。我尝试用另一个未显示的writeln（）语句替换“false code”。我很抱歉以前有人问过这个问题。非常感谢。

重写代码以避免使用if-then-else控件构造将更具声明性、惯用性和清晰性。例如：

% likelihood(Disease, PatientAge)
likelihood(malaria, y) :-
    writeln('Since patient is young, likelihood of malaria increases.').
likelihood(tuberculosis, e) :-
   writeln('Since patient is old, likelihood of tuberculosis increases.').

print_diagnostic(PatientAge) :-
    likelihood(Disease, PatientAge),
    write('Increased likelihood of '), write(Disease), nl.

不过，最好还是将写入的消息移动到调用

似然/2

谓词的谓词。例如：

% likelihood(Disease, PatientAge)
likelihood(malaria, y) :-
    writeln('Since patient is young, likelihood of malaria increases.').
likelihood(tuberculosis, e) :-
   writeln('Since patient is old, likelihood of tuberculosis increases.').

print_diagnostic(PatientAge) :-
    likelihood(Disease, PatientAge),
    write('Increased likelihood of '), write(Disease), nl.

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