let rec merge_in_sig outer_env namelist sg =
    let sig_env = Env.add_signature sg outer_env in
    merge_path sig_env namelist sg
  and merge_path sig_env namelist sig_items =
    match (namelist, sig_items) with
    | ([name], sig_items) ->
        merge_name sig_env name None sig_items
    | (s :: namelist, (Sig_module(id, _, md, rs, priv) as item) :: rem)
      when Ident.name id = s ->
        let ((path, _path_loc, tcstr), new_sig_items) =
          merge_in_sig (extract_sig sig_env loc md.md_type) namelist in
        real_ids := path :: !real_ids;
        let item =
          match md, constr with
          | {md_type = Mty_alias _}, (Pwith_module _ | Pwith_type _) ->
            item
          | _ ->
            let newmd = { md with md_type = Mty_signature new_sig_items } in
            Sig_module(id, Mp_present, newmd, rs, priv)
        in
        (path, lid, tcstr),
        item :: rem
    | (_, []) ->
        raise(Error(loc, sig_env, With_no_component lid.txt))
    | (_, item :: rem) ->
        let (cstr, items) = merge_path sig_env namelist rem in
        cstr, item :: items
  and merge_name sig_env name row_id sig_items =
    match sig_items with
    | (* all the other cases *)
    | [] ->
        raise(Error(loc, sig_env, With_no_component lid.txt))
    | item :: rem ->
        let cstr, items = merge_name sig_env name row_id rem in
        cstr, item :: items
  in