Add has-vertex?.

graph.rkt

@@ -22,6 +22,7 @@
   (require (prefix-in g: graph))
   (provide graph?
            directed-graph
+           has-vertex?
            has-edge?
            graphviz)
 
@@ -29,6 +30,8 @@
 
   (define (directed-graph es [ws #f])
     (graph (g:directed-graph es ws)))
+  (define (has-vertex? g v)
+    (g:has-vertex? (graph-g g) v))
   (define (has-edge? g u v)
     (g:has-edge? (graph-g g) u v))
   (define (graphviz g #:output [output #f] #:colors [colors #f])
@@ -37,6 +40,7 @@
 (require/typed 'graph-wrapper
   [#:opaque Graph graph?]
   [directed-graph (->* ((Listof (List Any Any))) ((Listof Any)) Graph)]
+  [has-vertex? (-> Graph Any Boolean)]
   [has-edge? (-> Graph Any Any Boolean)]
   [graphviz (->* (Graph)
                  (#:output Output-Port
@@ -45,4 +49,5 @@
 
 (define g (directed-graph '((a b) (b c))))
 (has-edge? g 'a 'c)
+(has-vertex? g 'a)
 (graphviz g)