class node s =
    object(self:'node)
        val mutable symbol = s
        method symbol      = symbol

        val mutable leaf  = false
        method leaf       = leaf
        method set_leaf b = leaf <- b

        val mutable transitions   = []
        method transitions        = transitions
        method get_transition key = List.assoc key transitions
        method add_transition (key,node) =
            transitions <- (key, node) :: transitions

        val mutable id  = 0
        method id       = id
        method set_id i = id <- i

        method private insert_suffix_tree root s suffix_chain =
            if String.length s > 0 then
                let key = Str.first_chars s 1 in
                let f acc current_node  =
                    try
                        (current_node#get_transition key) :: acc
                    with Not_found ->
                        let new_node : #node = new node key in
                        current_node#add_transition (key, new_node);
                        new_node :: acc
                in
                root#print_digraph;
                self#insert_suffix_tree root (Str.string_after s 1)

        (* without the coercions a bug seems to be triggered in ocaml *)
        (* self#insert_suffix_tree (self :> node> s [(self :> node)] *)
        method suffix_tree s =
            self#insert_suffix_tree self s [self]