create or replace function array_push(text[], text) returns text[] as $$
select coalesce($1 || $2, array[$2]);
$$ language sql;

create or replace function array_push(int[], int) returns int[] as $$
select coalesce($1 || $2, array[$2]);
$$ language sql;

orkut=# select array_push(array[1,2,3], 4);
 array_push
------------
 {1,2,3,4}
(1 registro)

orkut=# select array_push(null::int[], 2);
 array_push
------------
 {2}
(1 registro)

---------------------------------------------------------------------------

create or replace function array_pop(int[]) returns int[] as $$
select ($1)[array_lower($1, 1) + 1 : array_upper($1, 1)];
$$ language sql;

orkut=# select array_pop(array[1,2,3,4]);
 array_pop
-----------
 {2,3,4}
(1 registro)

orkut=# select array_pop(string_to_array('4,54,56,43', ',')::int[]);
 array_pop
------------
 {54,56,43}
(1 registro)

---------------------------------------------------------------------------

create or replace function array_first(int[]) returns int as $$
select ($1)[array_lower($1, 1)];
$$ language sql;

orkut=# select array_first(array[2,3,5]);
 array_first
-------------
           2
(1 registro)

---------------------------------------------------------------------------

create or replace function array_last(int[]) returns int as $$
select ($1)[array_upper($1, 1)];
$$ language sql;

orkut=# select array_last(array[1,3,5]);
 array_last
------------
          5
(1 registro)

---------------------------------------------------------------------------

create or replace function array_contains(int[], int) returns boolean as $$
select $2 = any($1);
$$ language sql;

orkut=# select array_contains(array[1,3,5], 4);
 array_contains
----------------
 f
(1 registro)

orkut=# select array_contains(array[1,3,5], 5);
 array_contains
----------------
 t
(1 registro)

---------------------------------------------------------------------------

create or replace function array_position(int[], int) returns int as $$
declare
  ii int;
begin
  if not $2 = any($1) then
    return null;
  end if;

  for ii in array_lower($1, 1)..array_upper($1, 1)
  loop
    if ($1)[ii] = $2 then
      return ii;
    end if;
  end loop;

  return null;
end
$$ language plpgsql;

orkut=# select array_position(array[1,3,5], 3);
 array_position
----------------
              2
(1 registro)

orkut=# select array_position(array[1,3,5], 5);
 array_position
----------------
              3
(1 registro)

orkut=# select array_position(array[1,3,5], 4);
 array_position
----------------

(1 registro)