球拍：如何在结构列表中的结构字段上应用过滤器

Question

My task is to write a function, inYear, which takes a number called year, and a list of event structures and produces a new list where each element is an event structure which occurred during year. I found this and tried defining a lambda function within the filter. See my event definitions/list, function and test below. The test fails and no elements get filtered out, it just returns the original list. What am I doing wrong?

(struct event (name day month year xlocation ylocation) #:transparent)

(define e1 (event "new years" 1 "Jan" 2021 0 0))
(define e2 (event "valentines" 14 "Feb" 2021 2 2))
(define e3 (event "my birthday" 6 "Mar" 2021 10 10))
(define e4 (event "tyler's birthday" 10 "Sep" 2020 20 20))
(define l1 '(e1 e2 e3 e4))

(define (inYear year events)
  (filter (lambda (e) (equal? (event-year e) year)) events))

(check-expect (inYear 2021 l1) '(e1 e2 e3))

Answer 1

The definition l1 evaluates to a list of symbols not a list of structs.

'(e1 e2 e3 e4) = (list 'e1 'e2 'e3 'e4)

You can convert the definition and the test output to be (list e1 e2 e3 e4) and (list e1 e2 e3) respectively.

Alternatively, you can use a quasi-quote-unquote combination like:

`(,e1 ,e2 ,e3 ,e4)

But this is less idiomatic for simply defining a list of structs.