method expr_list_cons =
                  fun simple f e ->
                    let (el, c) = o#mk_expr_list e
                    in
                      match c with
                      | None -> o#expr_list f el
                      | Some x ->
                          (if simple
                           then pp f "@[<2>(%a)@]"
                           else pp f "@[<2>%a@]")
                            (list o#under_semi#dot_expr " ::@ ") (el @ [ x ])