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)