method seq =
                  fun f e ->
                    let rec self right f e =
                      let go_right = self right
                      and go_left = self false
                      in
                        match e with
                        | Ast.ExLet (_, r, bi, e1) ->
                            if right
                            then
                              pp f "@[<2>let %a%a@];@ %a" o#rec_flag r
                                o#binding bi go_right e1
                            else pp f "(%a)" o#expr e
                        | Ast.ExSeq (_, e) -> go_right f e
                        | Ast.ExSem (_, e1, e2) ->
                            (pp f "%a;@ " go_left e1;
                             (match (right, e2) with
                              | (true, Ast.ExLet (_, r, bi, e3)) ->
                                  pp f "@[<2>let %a%a@];@ %a" o#rec_flag r
                                    o#binding bi go_right e3
                              | _ -> go_right f e2))
                        | e -> o#expr f e
                    in self true f e