recursive queries only with SQL procedures

I tested possibility of recursive queries only with SQL language (and SQL procedures)

postgres=# select * from rec_src;
id | parent |   v
----+--------+--------
 2 |      1 | rodic
 3 |      1 | rodic
 4 |      2 | dite
 5 |      2 | dite
 6 |      3 | dite
 7 |      6 | vnouce
 1 |      0 | root
(7 rows)

It's ugly, but it works :)

create or replace function empty2null(anyarray)
returns anyarray as $$
 select case
            when array_upper($1,1) is null
            then null
            else $1 end;
$$ language sql strict immutable;

create or replace function search_path(int)
returns varchar as $$
 select case
            when $1 is null
            then ''
            else search_path((select parent
                                 from rec_src
                                where id = $1)) || '.'|| $1 end;
$$ language sql;

create or replace function ls(int[], int,
                             out id int, out parent int, out path varchar, out v varchar )
returns setof record as $$
 select id, parent, search_path(id), repeat('  ',$2)|| v
    from rec_src
   where parent = any($1)
 union all
 select id, parent, path, v from ls(empty2null(array(select id
                                                        from rec_src
                                                       where parent = any($1))),
                                    $2 + 1);
$$ language sql volatile strict;
postgres=# select * from ls(array[0], 0) order by path;
id | parent |    path    |      v
----+--------+------------+--------------
 1 |      0 | .0.1       | root
 2 |      1 | .0.1.2     |   rodic
 4 |      2 | .0.1.2.4   |     dite
 5 |      2 | .0.1.2.5   |     dite
 3 |      1 | .0.1.3     |   rodic
 6 |      3 | .0.1.3.6   |     dite
 7 |      6 | .0.1.3.6.7 |       vnouce
(7 rows)