module EmptyCb: SigCb
with type t_env=unit
usefull when we don't want to have callbacks on the nodes
type
t_env
val button_one_press_on_graph : t_env -> unit
val button_two_press_on_graph : t_env -> unit
val button_three_press_on_graph : t_env -> unit
val button_one_press_on_node : t_env -> ViewGraph.t_node -> unit
val button_two_press_on_node : t_env -> ViewGraph.t_node -> unit
val button_three_press_on_node : t_env -> ViewGraph.t_node -> unit
val enter_node : t_env -> ViewGraph.t_node -> unit
val leave_node : t_env -> ViewGraph.t_node -> unit