Returning a setof integer

Hi, me again!
Im trying to return a setof integer from various functions and in all of
them the message when executed is:

WARNING: plpgsql: ERROR during compile of buscabcollibro near line 6
ERROR: missing .. at end of SQL expression

The functions are like this:

CREATE OR REPLACE FUNCTION BUSCabColLibro(VARCHAR) RETURNS SETOF INTEGER AS
'

DECLARE
Libro ALIAS FOR $1;
res INTEGER;
BEGIN

FOR res IN select cabidaCol from CARPagina where IdLibro =
CAST(Libro AS CHAR) LOOP
RETURN NEXT res;
END LOOP;
return;
END;

' LANGUAGE 'plpgsql';

Thanks a lot

JuanF
(a newbie migrating dbs)