ORDER BY with EXCEPT?

Howdy,

I was just updating a function in pgTAP that, given a schema name and
an array of function names, returns a set of those function names that
are not in the named schema. I got it working with a subquery, and
David Fetter suggested that I try an EXCEPT query instead. The only
problem is that it doesn't like my ORDER BY clause. The function is:

CREATE OR REPLACE FUNCTION mytest(NAME, NAME[]) RETURNS setof text AS
$$
SELECT quote_ident($2[i])
FROM generate_series(1, array_upper($2, 1)) AS s(i)
EXCEPT
SELECT quote_ident(p.proname)
FROM pg_catalog.pg_proc p
JOIN pg_catalog.pg_namespace n
ON p.pronamespace = n.oid
AND quote_ident(n.nspname) = quote_ident($1)
ORDER BY s.i
$$ LANGUAGE SQL;

When I run this, PostgreSQL 8.3 tells me:

ERROR: missing FROM-clause entry for table "s"
LINE 10: ORDER BY s.i

Um, really" Have I not put the ORDER BY clause in the right place? Is
this a bug?

Thanks,

David