;; The first three lines of this file were inserted by DrRacket. They record metadata
;; about the language level of this file in a form that our tools can easily process.
#reader(lib "htdp-intermediate-lambda-reader.ss" "lang")((modname day-of-date) (read-case-sensitive #t) (teachpacks ()) (htdp-settings #(#t constructor repeating-decimal #f #t none #f () #f)))
;; Integer Integer -> Boolean
;  Assume d != 0.
(define divisor?
  (λ(n d)
    (= (remainder n d) 0)))

;; Integer -> Boolean
(define leap-year?
  (λ(y)
    (and (divisor? y 400)
         (and (divisor? y 4)
              (not (divisor? y 100))))))



;; String -> Integer
;  Assume m is one of : January, ..., December
(define month-key
  (λ(m)
    (cond ((equal? m "January") 1)
          ((equal? m "February") 4)
          ((equal? m "March") 4)
          ((equal? m "April") 0)
          ((equal? m "May") 2)
          ((equal? m "June") 5)
          ((equal? m "July") 0)
          ((equal? m "August") 3)
          ((equal? m "October") 1)
          ((equal? m "November") 4)
          (else 6))))   ;; September and December


;; Integer -> Integer
;; Assume 1700 <= year < 3000
(define century-code
  (λ(year)
    (cond ((< year 1800) 4)
          ((< year 1900) 2)
          ((< year 2000) 0)
          (else 6))))


;; Integer -> String
;  Assume 0 <= n <= 6.
(define num-to-day
  (λ(n)
    (cond ((= n 0) "Sat.")
          ((= n 1) "Sun.")
          ((= n 2) "Mon.")
          ((= n 3) "Tues.")
          ((= n 4) "Wed.")
          ((= n 5) "Thurs.")
          (else "Fri."))))




;; String Integer Integer -> String
;  Assume m is one of : January, ..., December
;         1 <= d <= 31
;         1699 < y < 3000
(define day-of-date
  (λ(m d y)
   (num-to-day (remainder (+ (quotient (remainder y 100) 4)
                             d
                             (month-key m)
                             (if (and (or (equal? m "January") (equal? m "February"))
                                      (leap-year? y))
                                 -1
                                 0)
                             (century-code y)
                             (remainder y 100))
                          7))))






(day-of-date "March" 5 2014)