;;
;; CSE 341 -- Racket structs
;;
;; For more information see http://docs.racket-lang.org/guide/define-struct.html

#lang racket


(struct point (x y))

;; we now have accessors and tests defined:
(define p (point 10 10))

;; try these:
;; (point? p)
;; (point-x p)
;; (point-y p)
;; (point-y p)

(define (dist p1 p2)
  (let ([dx (- (point-x p1) (point-x p2))]
        [dy (- (point-y p1) (point-y p2))])
    (sqrt (+ (* dx dx) (* dy dy)))))

(define a (point 0 0))
(define b (point 3 4))

;; (dist a b)

;; a struct is different from the other datatypes in Racket:
(define (what-is-it v)
  (cond [(number? v) 1]
        [(procedure? v) 2]
        [(cons? v) 3]
        [(string? v) 4]
        [(symbol? v) 5]
        [(null? v) 6]
        [else 7]))

;; points as defined above are opaque (try printing one)
;; add a keyword transparent to show the fields: 

(struct tpoint (x y) #:transparent)

;; there are many other options for structs -- another declares
;; that all fields are mutable:

(struct mpoint (x y) #:mutable)

(define m (mpoint 10 10))

;; mpoints have all of the functions as points, plus setters:

;; (set-mpoint-x! m 100)
;; (set-mpoint-y! m 200)