triggers

I'm currently running a database on Oracle and would like to make my
application portable to the PostgreSQL database.  Converting the tables
(specifically the attribute types) is fairly easy but I've run into a
problem with database triggers.

My application is designed so that insertions/updates to certain tables
only provide a limited number of attributes and an Oracle trigger fills
in the other attributes.  For example, one table may have id and name
attributes but when the application inserts new records it only provides
the name value and a trigger fills in the id value (from a sequence number).

I started looking at the trigger support in PostgreSQL and found what I
needed except I'm not sure how to write the "body" of the trigger.  In
Oracle I write PL/SQL but it seems I may have to write C code on the
PostgreSQL side.  Is this true?  Is there a PostgreSQL procedural language
that I can write the body in?

Thanks,
Kevin.