Recursive function that receives a list of IDs and returns all child IDs

hello pgsql fans out there,

i've already created a function that returns a list of IDs of all sub-samples based on a given sample ID. this works
fine.now i like to extend this function so that it can receive a list of sample IDs. e.g.: 

fn_get_subsamples(IN sample_numbers SETOF integer)


here is the existing function:

CREATE OR REPLACE FUNCTION fn_get_subsamples(IN sample_number integer)
  RETURNS SETOF integer AS
$BODY$
    WITH RECURSIVE recursetree(sample_number) AS (
      SELECT sample_number
      FROM sample
      WHERE parent_sample = $1

      UNION ALL

      SELECT t.sample_number
      FROM sample t
      JOIN recursetree rt ON rt.sample_number = t.parent_sample
    )

    SELECT sample_number
    FROM recursetree;
$BODY$
  LANGUAGE sql VOLATILE



thanks a lot for every hint!
sven
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