;; 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-beginner-reader.ss" "lang")((modname LectureSept15) (read-case-sensitive #t) (teachpacks ()) (htdp-settings #(#t constructor repeating-decimal #f #t none #f () #t)))
;; a ListOfNumber is one of
;;   empty
;; (cons Number ListOFNumber)

;; extract-positives:  ListOfNumber -> List)fNumber
;;
(define (extract-positives alon)
  (cond [(empty? alon)  empty    ]
        [(cons? alon)    (if (>= (first alon) 0)
                             (cons (first alon) (extract-positives (rest alon)))
                             (extract-positives (rest alon)))]))


(check-expect (extract-positives empty) empty)
(check-expect (extract-positives (cons -5 (cons -3 empty))) empty)
(check-expect (extract-positives (cons 7 (cons 2 empty))) (cons 7 (cons 2 empty)))
(check-expect (extract-positives (cons -3 (cons 3 (cons 0 (cons -5 empty))))) (cons 3 (cons 0 empty)))




(define-struct course (dept coursenum term sections seats))
;; a Course is a (make-course String Natural String Natural Natural)
;;  interp:   a course where
;;   dept is the department
;;   coursenum is the course number
;;   term is the term the course is offered
;;   sections is the number of sections
;;   seats is the number of seats per section

;; examples
(define MA2201 (make-course "MA" 2201 "A" 8 30))
(define CS1101 (make-course "CS" 1101 "C" 6 25))

;;; fcn-for-course:  Course ->
;;;
;(define (fcn-for-course a-course)
;  (course-dept a-course)
;  (course-coursenum a-course)
;  (course-term a-course)
;  (course-sections a-course)
;  (course-seats a-course))



;; a ListOfCourse is one of
;;   empty
;;   (cons Course ListOfCourse)


;; examples
(define SCHED (cons MA2201 (cons CS1101 empty)))



;;; fcn-for-loc:  ListOfCourse ->
;;;
;(define (fcn-for-loc aloc)
;  (cond [(empty? aloc)      ]
;        [(cons? aloc)  (...(fcn-for-course (first aloc))
;                           (fcn-for-loc (rest aloc)))]))





;; course-capacity:  ListOfCourse -> Natural
;; produces the total number of seats in all sections in all courses in the list
(define (course-capacity aloc)
  (cond [(empty? aloc)   0   ]
        [(cons? aloc)  (+ (capacity-of-one (first aloc))
                          (course-capacity (rest aloc)))]))


;; capacity-of-one:  Course -> Natural
;; produces the number of all seats in all sections of the course
(define (capacity-of-one a-course)  
  (* (course-sections a-course)
     (course-seats a-course)))

(check-expect (capacity-of-one MA2201) 240)



(check-expect (course-capacity empty) 0)
(check-expect (course-capacity SCHED) 390)