Use records instead of conss for nodes, alist for graphs

demo.scm

@@ -1,19 +1,10 @@
-(use-modules (graphgif))
+(use-modules (graphgif)
+	     (srfi srfi-9 gnu)
+	     (ice-9 copy-tree))
 
 (define red (create-color 1 0 0))
 
-(define my-graph
-  `(((10 . 10) (1))
-    ((30 . 20) () ,red)))
-
-(define more-complex-graph
-  `(((10 . 10) ()) 
-    ((40 . 10) (0))
-    ((25 . 25) (0 1))
-    ((10 . 40) (0 2 4))
-    ((40 . 40) (1 2 3))))
-
-(let* ([graph1 (generate-web 10 10)]
-       [graph2 (list-copy graph1)])
-  (set-car! graph2 (append (car graph2) `(,red)))
-  (write-graphs-to-file (list graph1 graph2) "graph.gif"))
+(define graph1 (generate-web 10 10))
+(define graph2 (copy-tree graph1))
+(assq-set! graph2 0 (set-node-color (assq-ref graph2 0) red))
+(write-graphs-to-file (list graph1 graph2) "graph.gif")