open Graph


let rec clone_nodes gr = 
  n_fold gr (fun g id -> new_node g id) empty_graph

let gmap gr f = 
  e_fold gr (
    fun g id_s id_d cost -> new_arc g id_s id_d (f cost) 
  ) (clone_nodes gr)

let add_arc gr id1 id2 n = 
  let lbl = find_arc gr id1 id2 in
  match lbl with
  | None -> new_arc gr id1 id2 n
  | Some cost -> new_arc gr id1 id2 (n + cost)