SCHEME [4 marks] Define a procedure called valid_date? that takes three arguments representing the year, month,...

SCHEME

[4 marks] Define a procedure called valid_date? that takes three arguments representing the year, month, and day respectively. The procedure should return true (#t) if the values are numbers representing a valid date and false (#f) otherwise.
E.g. (valid_date? 2014 10 3) → #t
E.g. (valid_date? 2016 2 29) → #t
E.g. (valid_date? -3000 14 87) → #f
E.g. (valid_date? "2019" "September" "7th") → #f

Expert Solution

; this will return true (#t) if year is leap year
; else false (#f)
(define (leap_year? year)
   ; if not number
   (cond ((not (integer? year)) #f)
       ; else part
       (else
           (or
               (and
                   (equal? (remainder year 4) 0)
                   (not (equal? (remainder year 100) 0))
               )
               (equal? (remainder year 400) 0)
           )
       )
   )
)

; (leap_year? 1700)
; (leap_year? 1800)
; (leap_year? 1900)
; (leap_year? 1600)
; (leap_year? 2000)

(define (valid_date? y m day)
   (cond ((and (integer? y) (integer? m) (integer? day))
               ; validation of y, m, d
               (cond ((and (>= y 1) (and (>= m 1) (<= m 12)) (and (>= day 1) (<= day 31)))
                       ; check is m = 2
                           (cond ((equal? m 2)
                                       ;; check is year is leap year
                                       (cond ((leap_year? y) (and (>= day 1) (<= day 29)))
                                           ; if y is not leap year
                                           (else (and (>= day 1) (<= day 28)))
                                       )
                                   )
                               ; check is m even
                               ((equal? (remainder m 2) 0) (and (>= day 1) (<= day 30)))
                               ; if m is odd
                               (else (and (>= day 1) (<= day 31)))
                           )
                       )
                   (else #f)
               )
           )
           (else #f)
   )
)

; (valid_date? 2014 10 3) → #t
; (valid_date? 2016 2 29) → #t
; (valid_date? -3000 14 87) → #f
; (valid_date? "2019" "September" "7th") → #f

venereology answered 5 hours ago

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