select prosrc from pg_proc where proname='test'

  drop function test(anyelement,anyelement,numeric)

  create or replace function calculate_speed(end_time anyelement,begin_time anyelement,length numeric) RETURNS numeric  as

   $$

      declare

      total_second numeric;

      begin

             select extract(epoch from((end_time::timestamp - begin_time)))/3.6 into total_second;

             return round(length::numeric/total_second::numeric,3);

      end;

   $$ LANGUAGE plpgsql;