Question

我想写一条规则，告诉我一个人是否通过了一个主题。通过的最低成绩是40％。我已经成功地写了一个谓词，告诉我这个人是否通过，但我很困惑，我怎么会得到它也给我个人/主题对。即朱莉/历史。提前谢谢。

% studies( Person, Subject)
% -------------------------
studies( julie, history).
studies( pete, chemistry).


% marks( Person, CourseWork, Exam)
% --------------------------------
marks( julie, 77, 63).
marks( pete, 55, 21).

passed(Person,_Subj):-
%get student work and exam grades
marks(Person, Work, Exam),
%calculate the final student grade
Perc is Work*0.25 + Exam*0.75,
%see if percentage is over 40%
Perc >= 40.

Answer 1

您的事实数据库的设计方式使得一个人只能参与一个主题（否则无法知道什么标记是针对哪个主题）。

考虑到这一点，这里是对代码的简单修改：

passed(Person, Subj):-
    studies(Person, Subj),
    marks(Person, Work, Exam),
    Perc is Work*0.25 + Exam*0.75,
    Perc >= 40.

试运行：

?- passed(X, Y).
X = julie,
Y = history ;
false.

Answer 2

修改您的passed谓词，以提供通过的Person和Subj对：

passed(Person, Subj):-
    %get student work and exam grades
    marks(Person, Work, Exam),
    %calculate the final student grade
    Perc is Work*0.25 + Exam*0.75,
    %see if percentage is over 40%
    Perc >= 40,
    studies(Person, Subj).

然后使用findall/3收集所有内容：

passing(PassingStudents) :-
    findall(Person/Subj, passed(Person, Subj), PassingStudents).

在Prolog中写规则

2 个答案: