;; 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-advanced-reader.ss" "lang")((modname week8_w_full) (read-case-sensitive #t) (teachpacks ((lib "image.ss" "teachpack" "2htdp"))) (htdp-settings #(#t constructor repeating-decimal #t #t none #f ((lib "image.ss" "teachpack" "2htdp")))))

(define-struct graph (nodes neighbor))

(define (add-edge g a b) 
   (make-graph (graph-nodes g)
       (lambda (node) (append ((graph-neighbor g) node) (cond [(symbol=? node a) (list b)] [else empty])))))

(define mygraph
(make-graph
 '(a b c d e f g)
  (lambda (node)
   (cond
    [(symbol=? node 'a) '(b)]
    [(symbol=? node 'b) '(d e)]
    [(symbol=? node 'c) '(e f)]
    [(member node '(d e f)) '(g)]
    [(symbol=? node 'g) '()])))

)

(check-expect ((graph-neighbor (add-edge mygraph 'c 'd)) 'c) '(e f d))
(check-expect ((graph-neighbor (add-edge mygraph 'c 'd)) 'b) '(d e))