function language type?

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

I am trying to write a function in the SQL procedural language. But when I
use type plpgsql, as the user's guide says, I get this error:

ERROR: Unrecognized language specified in a CREATE FUNCTION: 'plpgsql'.
Recognized languages are sql, C, internal and the created procedural
languages.

If I try setting the language to type sql, I get:

ERROR: parser: parse error at or near "alias"

The only occurance of the string alias is in these four lines, which are
below a DECLARE line, which is the first line of the function:

osec ALIAS FOR $1;
dsec ALIAS FOR $2;
who ALIAS FOR $3;
avoids ALIAS FOR $4;

And yes, the function has four parameters.

Any ideas?

Ian

P.S. Please keep the CC on this message, I want replies at both mailboxes.
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.0.1 (GNU/Linux)
Comment: For info see http://www.gnupg.org

iD8DBQE5fSeJfn9ub9ZE1xoRAkshAJ9zzq3oq2Qu4NsICfNJmwelA58/YgCfcFyc
KjcG5GHUjCZOeXlURbDOqk4=
=Gn4j
-----END PGP SIGNATURE-----