;; 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 lect08-dist) (read-case-sensitive #t) (teachpacks ()) (htdp-settings #(#t constructor repeating-decimal #f #t none #f ())))
; Data definition:
; A Book is:
;  (make-book    [string]   [string]    [int]       [boolean])

(define-struct book (title author pages copyrighted?))

#|
; `define-struct` is like Java `class { ...}` but with only fields.

class Book {
   String title;
   String author;
   int pages;
   boolean isCopyrighted;
  }
|#

; Note that in Java, calling a constructor is not *quite* like
; calling most functions:
; it uses keyword `new`.



; new Book( "Goosebumps", "Stine",  37, true )
; ((new Book( "Goosebumps", "Stine",  37, true )).toString()).length() 
; (new Book("Goosebumps", "Stine",  37, true)).author
(define scary (make-book "Goosebumps" "Stine" 37 true))
(make-book "Moby Dick" "Melville" 972 false)

(book-title (make-book "Moby Dick" "Melville" 972 false))



; getters            
;   (corresponding to Java .author, .title, .pages, .isCopyrighted)
; book-title :  book -> string
; book-author : book -> string
; book-pages: book -> int
; book-copyrighted? : book -> boolean

; predicate:
;   book? : ANY -> boolean

; WHEN YOU USE define-struct,
; RACKET DEFINES THE CONSTRUCTOR, GETTERS (ACCESSORS), and
; A PREDICATE FUNCTION FOR YOU.
; They're regular functions (no special syntax to call them).

;;;;;;;;;;;;
(define-struct dvd (title runtime rating))
; A DVD is:
;  (make-dvd [string] [number] [symbol])
;
; the constructor:
;   make-dvd
; getters:
;   dvd-title
;   dvd-runtime
;   dvd-rating

; Examples of the data:

(make-dvd "Once" 100 'PG-13)

(define fave (make-dvd "Once" 100 'PG-13))
(dvd-runtime fave)

(check-expect (should-watch? fave) true)
(check-expect (should-watch? (make-dvd "9" 182 'R)) true)
(check-expect (should-watch? (make-dvd "Schindler's List" 182 'PG-13)) false)
(check-expect (should-watch? (make-dvd "Scream" 85 'R)) true)

; should-watch? : dvd -> boolean
(define (should-watch? some-dvd)
  (or (< (dvd-runtime some-dvd) 110)
      (symbol=? (dvd-rating some-dvd) 'R)))


; TEMPLATE for any function handling a dvd:
; func-for-dvd : dvd -> boolean
;
(define (func-for-dvd a-dvd)
  ...(dvd-runtime a-dvd)
  ...(dvd-rating some-dvd)
  ...(dvd-title a-dvd))