;; The first three lines of this file were inserted by DrScheme. 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 lect03b) (read-case-sensitive #t) (teachpacks ((lib "universe.ss" "teachpack" "2htdp"))) (htdp-settings #(#t constructor repeating-decimal #f #t none #f ((lib "universe.ss" "teachpack" "2htdp")))))
; A book is:
;   (make-book [string] [string] [number] [boolean])
;
(define-struct book (title author pages copyR?))

; Examples of the data:
(make-book "The Soul of Wit" "Shorty" 0 false)
(define b1 (make-book "The Cat in the Hat" "Seuss" 31 true))


; Note that 'define-struct' automagically creates
; functions for us:
; Constructor:
;   make-book: string, string, number, boolean -> book
; Selectors:
;   book-title  : book -> string
;   book-author : book -> string
;   book-pages  : book -> number
;   book-copyR? : book -> boolean
; Predicate:
;   book? : ANY -> boolean


; read-time: book -> number
; How long does it take to read `a-book`, in hours?
;
#;(define (read-time a-book)
  -99)

(check-expect (read-time (make-book "The Soul of Wit" "Shorty" 0 false)) 0)
(check-expect (read-time b1) (+ 1 2/60))

;;; AFTER making the test cases, we go back and write the code:

; read-time: book -> number
; How long does it take to read the book, in hours?
;
(define (read-time a-book)
  (* (book-pages a-book) 2 1/60))