Help with simple function

I need some help.  I am trying to get a very simple function written to help our developers.  Unfortunetly, the language we are developing in is giving us some grief over trying to do a "select to_char((current_date - inteval '1 day'),'yyyymmdd') into x".  It is complaining about the use of the work interval.

Anyway, I thought, no problem, I'll just create a date increment and date decrement set of functions.  However, I can not get them to work.  Can someone please point out what is wrong?

CREATE OR REPLACE FUNCTION "public"."date_dec" (date, integer) RETURNS varchar AS'
declare
       startDate alias for $1;
       numDays alias for $2;
       retDate varchar(8);
begin
  select to_char((startDate - interval ''numDays day''),''yyyymmdd'') into retDate;
  return retDate;
end;
'LANGUAGE 'plpgsql' VOLATILE CALLED ON NULL INPUT SECURITY INVOKER;


When I try to run this, it complains about numDays - "Error:  Bad interval external representation 'numDays day'".  Is there anyway around this?  I am trying to keep the function generic so that our developers can use it to calculate any date range.

Thanks for any help,

Chris

PG7.3.4 (8.1.1 upgrade happening next month)