method private print_edge (e: 'e DGraphViewItem.view_edge) =
let v1, v2 = Service.CallG.E.src e#edge, Service.CallG.E.dst e#edge in
Options.debug "edge from \"%s\" (service %d) to \"%s\" (service %d): %s@."
(Service.TP.vertex_name v1) (self#service (self#src e))
(Service.TP.vertex_name v2) (self#service (self#dst e))
(match Service.CallG.E.label e#edge with
| Service.Inter_services -> "inter services"
| Service.Inter_functions -> "inter functions"
| Service.Function_to_service -> "function to service")