Lambda 如何找到相应的列表？

到目前为止，我已经找到了相应的课程，如下所示：

(define-struct course (subject number title))
;; A Course is a (make-course Sym Nat Str)
;; where: ;; subject is the subject of the course
;; number is the course number of the course
;; title is the of the course

(define-struct student (id name age courses))
;; A Student is a (make-student Nat Str Nat (listof Course))
;; where: ;; id is the student id for the student
;; name is the name of the student
;; age is the age of the student
;; courses is a list, with one element for each different course
;; the students are enrolled in 

(define math135 (make-course 'MATH 135 "Algebra"))
(define chem101 (make-course 'CHEM 101 "Intro to chemistry"))
(define eco638  (make-course 'ECO 638 "Econ"))
(define arts392 (make-course 'ARTS 392 "Arts"))
(define cs101 (make-course 'CS 101 "Intro to CS"))

(define stu1 (make-student 373647 "Mary" 40 (list math135 eco638)))
(define stu2 (make-student 367339 "Tony" 21 (list chem101 cs101 math135)))
(define stu3 (make-student 362927 "Joy"  35 (list chem101 arts392)))

(define students (list stu1 stu2 stu3))

那么我应该怎么做才能产生相应的学生名单呢？ 比如说,

(filter (lambda (lst)
          (and (symbol? coursesub (course-subject lst))
               (equal? coursenum (course-number lst)))) los)

---

筛选那些课程列表中的课程与

cname

，

cnum

匹配的学生

(check-expect (students-in-course 'MATH 135 students) (list stu1 stu2))

编辑：版本2（无本地）：

编辑：版本3（无助手）：

---

谢谢！但是，如果不允许使用局部递归或显式递归，那么我们应该怎么做？对于前者，请参见编辑。我不确定你所说的“显式递归”是什么意思，这里没有递归调用。很抱歉我解释得不清楚。实际上，对于这个问题，不允许同时使用命名的helper函数，也就是说，我们只能使用lambda和抽象列表函数。我只是不知道在我确定了相应的课程列表之后（你在课程匹配中做了什么？），下一步我应该做什么。谢谢你的耐心！替换对

课程匹配的调用？

它的主体应该会这样做。请参阅编辑。我认为stackoverflow中已经有类似的问题（搜索结构）。

; Symbol Number [List-of Student] -> [List-of Student]
(define (students-in-course.v2 coursesub coursenum lst)
  (local ((define (course-match? course)
            (and (symbol=? (course-subject course) coursesub)
                 (= (course-number course) coursenum))))
    (filter (λ (student) (ormap course-match? (student-courses student))) lst)))

; Symbol Number Course -> Boolean
(define (course-match? coursesub coursenum course)
  (and (symbol=? (course-subject course) coursesub)
       (= (course-number course) coursenum)))

; Symbol Number [List-of Student] -> [List-of Student]
(define (students-in-course.v2 coursesub coursenum lst)
  (filter (λ (student) (ormap (λ (course) (course-match? coursesub coursenum course))
                              (student-courses student)))
          lst))

; Symbol Number [List-of Student] -> [List-of Student]
(define (students-in-course.v2 coursesub coursenum lst)
  (filter (λ (student)
            (ormap (λ (course)
                     (and (symbol=? (course-subject course) coursesub)
                          (= (course-number course) coursenum)))
                   (student-courses student)))
          lst))