;; 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 lect11-union-of-structs) (read-case-sensitive #t) (teachpacks ()) (htdp-settings #(#t constructor repeating-decimal #f #t none #f ())))
;; a book has info:
;; title, author, # of pages, is copyrighted?

; Data Definiton:
; A book is:
;    (make-book [string] [string] [natural] [boolean])
(define-struct book (title author num-pages is-copyrighted?))

; Examples of the data
(define b0 (make-book "Soul and Wit" "Barland" 0 #false))
(define b1 (make-book "The Cat in the Hat" "Seuss" 37 #true))

; `define-struct` actually introduces additional functions:
; a constructor
; and four getters ("selectors").
; In this case, the constructor is named
;   make-book : string, string, natural, boolean -> book
; and the getters are named
;   book-title : book -> string
;   book-author
;   book-num-pages
;   book-is-copyrighted?

(book-title (make-book "The Cat in the Hat" "Seuss" 37 #true))
(book-is-copyrighted? b0)

;;; template (we'll come back)

; func-for-book : book -> ...
;
(define (func-for-book a-book)
  (... (book-title a-book)
   ... (book-author a-book)
   ... (book-num-pages a-book)
   ... (book-is-copyrighted? a-book)))



; reading-time : book -> non-negative real
; The amount of time it takes the average reader to read a book (in minutes)
;
(define (reading-time a-book)
  (* (book-num-pages a-book) 2))



(check-expect (reading-time (make-book "The Cat in the Hat" "Seuss" 37 #true))
              74)
(check-expect (reading-time b0) 0)



; book->string : book -> string
; Return a string-representation of a book struct, user-friendly.
(define (book->string a-book)
  (string-append (book-title a-book)
                 ", by "
                 (book-author a-book)
                 " ("
                 (number->string (book-num-pages a-book))
                 "pp)"
                 (if (book-is-copyrighted? a-book) ", ©" "")))

  
(check-expect (book->string (make-book "The Cat in the Hat" "Seuss" 37 #true))
              "The Cat in the Hat, by Seuss (37pp), ©")
(check-expect (book->string b0)
              "Soul and Wit, by Barland (0pp)")




; derive-from
; Create a brand new book, based on an original.
; The result's author will be the original author & the new-author,
; and the result has pages added to the original.
;



(check-expect (derive-from b1 "Sauced" 3)
              (make-book "Son of The Cat in the Hat" "Seuss & Sauced" 40 #false))
(check-expect (derive-from b0 "Freund" 0)
              (make-book "Son of Soul and Wit" "Barland & Freund" 0 #false))




; A DVD is:






; Data def'n:
; A lib-item is:
;  - a book, OR
;  - a dvd


; template: code for ANY function which processes a lib-item.











; func-for-lib-item : lib-item -> ...?
;
(define (func-for-lib-item an-item)
  (cond [(book? an-item) ...]
        [(dvd? an-item)  ...]))










; func-for-lib-item : lib-item -> ...?
;
(define (func-for-lib-item an-item)
  (cond [(book? an-item) (... (book-title an-item)
                          ... (book-author an-item)
                          ... (book-num-pages an-item)
                          ... (book-copyrighted? an-item))]
        [(dvd? an-item)  (... (dvd-title an-item)
                          ... (dvd-length an-item)
                          ... (dvd-rating an-item))]))





; time-to-waste : lib-item -> non-negative real
; Return how much time I can waste from this library item.
(define (time-to-waste an-item)
  ; time-to-waste: a dvd's run time plus 5min to get it going,
  ;  or (for a book) its reading time pluse 1min to read back cover.
  9999.99)