Select parser at runtime ....

Hello, I'm pretty new to PostgreSQL, (I'm a (young) oracle DBA)

We need to work with Oracle (some heavy client of our society want Oracle
for security or maintenance), but we want to work with PostgreSQL too, cause
it's more performant, less administration, ... in few words : It's the
future
But before PostgreSQL rule the world, we want to develop once and deploy
twice, so I create some function ( now() and nextval() under oracle ) to
enhanced Oracle and PostgreSQL compatibily ...
But I have a big problem : PostgreSQL doesn't allow Oracle style outer join,
and Oracle doesn't allow Postgres style ... So, if someone can do something,
I will be very greatfull ...

Other compatibily problems : reserved words, create function syntax,
datatypes are not a problem, I can workaround.

Thanx in advance ...