我一直得到錯誤first: expects a non-empty list
給出:(make-subject (make-person 22 'm 'MW17K) (list 220 301 189 272 311))
當啓動我的程序,只是無法找出原因。第一:預計非空列表
;;equals 25 but my code keeps erroring. please help
(person-age (subject-person (first sub)))
(define-struct person (age sex code))
(define-struct subject (person times))
(define VP01 (make-subject (make-person 22 'm 'MW17K) (list 220 301 189 272 311)))
(define VP02 (make-subject (make-person 25 'f 'MP25G) (list 234 197 253 257 206)))
(define VP03 (make-subject (make-person 23 'f 'CT03R) (list 197 202 214 222 233)))
(define VP04 (make-subject (make-person 20 'm 'MM09R) (list 273 314 257 264 217)))
(define VP05 (make-subject (make-person 19 'm 'KR22I) (list 198 197 228 253 199)))
(define VP06 (make-subject (make-person 26 'm 'FR01B) (list 212 204 289 294 223)))
(define VP07 (make-subject (make-person 28 'f 'RA15R) (list 258 323 189 247 303)))
(define VP08 (make-subject (make-person 22 'm 'RP18R) (list 221 307 182 271 316)))
(define VP09 (make-subject (make-person 24 'f 'GH31W) (list 230 295 304 264 237)))
(define VP10 (make-subject (make-person 19 'f 'OM29Q) (list 299 194 242 303 243)))
(define subjects (list VP01 VP02 VP03 VP04 VP05 VP06 VP07 VP08 VP09 VP10))
(define (idk sub)
(cond
[(empty? sub) empty]
[(< (person-age (subject-person (first sub)))
(person-age (subject-person (first (rest sub)))))
(idk (first sub))]
[else (idk (first (rest sub)))]))
(idk subjects)
你」在進入第二個或第三個條件表達式之前,需要確保你總是有兩個人。錯誤是告訴你你試圖將空列表傳遞給'(first)' - 這種情況發生在'sub'只有一個成員的情況下。 – pdoherty926