Prolog - 如果满足条件则添加到总计

Question

我正在尝试编写一个执行此操作的 Prolog 函数:

Takes three parameters: a name, a course list, and an integer. The integer should be equal to the number of projects in the list that include the name.

编辑

我已经稍微清理了我的代码:

studentCount(Name, [], 0).
studentCount(Name, [Project|MoreProjects], Sum) :-
    nameInProject(Name, Project),
    studentCount(Name, MoreProjects, Sum),
    NewSum is Sum + 1.
studentCount(Name, [Project|MoreProjects], Sum) :-
    not(nameInProject(Name, Project)),
    studentCount(Name, MoreProjects, Sum).

nameInProject(Name, Name1+Name2+_) :-
    Name == Name1;
    Name == Name2.

它将 N 绑定(bind)到列表的长度，但是，每次我调用它时:

?- studentCount(x,[x+y+1,a+b+2,c+x+3],N)
N = 3.

由于原子 x 在两个项目中可见，它应该将 N 绑定(bind)到 2。不确定我应该在哪里寻找错误。

Answer 1

也许你应该使用以下内容:

studentCount(Name, [], 0).
studentCount(Name, [Project|MoreProjects], NewSum) :-
    nameInProject(Name, Project),
    studentCount(Name, MoreProjects, Sum),
    NewSum is Sum + 1.
studentCount(Name, [Project|MoreProjects], Sum) :-
    not(nameInProject(Name, Project)),
    studentCount(Name, MoreProjects, Sum).

% checks if name is in the project
nameInProject(Name, Name1+Name2+_) :-
    Name == Name1;
    Name == Name2.

因为你用来递增 Sum 的 NewSum 是你最后需要得到的。

---

编辑:我现在没有 prolog 解释器，但你甚至可以尝试以下操作:

studentCount(Name, [], 0).
studentCount(Name, [Project|MoreProjects], NewSum) :-
    nameInProject(Name, Project),
    studentCount(Name, MoreProjects, Sum),
    NewSum is Sum + 1;
    studentCount(Name, MoreProjects, NewSum).

% checks if name is in the project
nameInProject(Name, Name1+Name2+_) :-
    Name == Name1;
    Name == Name2.