for row in select loop question

The following function does not work:

CREATE FUNCTION InstallPermissions(varchar, varchar) RETURNS int2 AS 'DECLARE                options ALIAS FOR $1;
usernameALIAS FOR $2;
 
BEGINFOR row IN select * from pg_tables LOOP            REVOKE ALL ON row.tablename FROM username;      GRANT options
onrow.tablename TO username;END LOOP;return 0;END; ' LANGUAGE 'plpgsql';
 

"select InstallPermissions('test1', 'test2);"  returns an error at "select".
Any suggestions on how to eliminate the error?

Thanks, Michael