(* Simple graph traversal (BFS or DFS) *)
let val q: queue = new_queue()
    (* visited is the set of vertices that have been visited. *)
    val visited: vertexSet = create_vertexSet()

    (* Expand the visited set to contain everything v goes to,
     * and add newly seen vertices to the queue. *)
    fun expand(v: vertex) =
      let fun handle_edge(e: edge): unit =
        let val (v, v') = Graph.edgeInfo(e) in
          if not (member(visited,v'))
            then ( add(visited, v');
                   enqueue(q, v') )
            else ()
        end
      in
        app handle_edge (Graph.outgoing(v))
      end
in
  add(visited, v0);
  enqueue(q, v0);
  while (not (empty_queue(q))) do expand(dequeue(q))
end