;; 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 structures) (read-case-sensitive #t) (teachpacks ((lib "draw.ss" "teachpack" "htdp"))) (htdp-settings #8(#t constructor repeating-decimal #f #t none #f ((lib "draw.ss" "teachpack" "htdp")))))

;; a position (posn) represents a dot (pixel) by its x and y 
;; coordinates. Use a function make-posn to create a new
;; position and posn-x, posn-y to get x and y coordinates of
;; an already created position

(make-posn 5 6)
(define pos (make-posn 3 4))
pos
(posn-x pos)

;; distance-to-0 : posn  ->  number
;; to compute the distance of a-posn to the origin 
(define (distance-to-0 a-posn)
  (sqrt
    (+ (sqr (posn-x a-posn))
       (sqr (posn-y a-posn)))))

;; Tests 
(distance-to-0 (make-posn 3 4))
;; expected value 
5

(distance-to-0 (make-posn 8 6))
;; expected value 
10

(distance-to-0 (make-posn 5 12))
;; expected value 
13

;; drawing with positions -- teachpack draw.ss required
(define pixel-10-10 (make-posn 10 10))
(define pixel-100-10 (make-posn 100 10))
(define pixel-150-150 (make-posn 150 150))
(define pixel-10-20 (make-posn 10 20))

;; open the canvas
(start 300 300)
(draw-solid-line pixel-10-10 pixel-100-10 'green)
(draw-solid-disk pixel-150-150 50 'orange)
(draw-solid-rect pixel-10-20 100 1500 'blue)