Using SETOF in plpgsql function

Hello,

I'd like to return a set of integer in an pl/pgsql function. How can I
do that ?

I've tried things like that, put I've an error when executing :

CREATE FUNCTION SP_UPLES() RETURNS setof INTEGER AS '   DECLARE ID INTEGER;
BEGIN   select a into id from foo;   return ID ;
END;      

CREATE FUNCTION SP_UPLES() RETURNS setof INTEGER AS '   DECLARE ID setof INTEGER;
BEGIN   select a into id from foo;   return ID ;
END; 

CREATE FUNCTION SP_UPLES() RETURNS setof INTEGER AS '
BEGIN   select a into id from foo;   return select a from foo; 
END;           

Any help is welcomed.
Thanks.