CREATE TYPE example needed

Hi all,

I am looking for a way to create a VARCHAR2 (oracle) type so I can use the same SQL to create my tables in either
Oracle
or Postgresql.  Does anyone have a working example?

I have tried the following with no luck

create type varchar2 (input=varcharin,output=varcharout,INTERNALLENGTH=VARIABLE);
ERROR:  TypeCreate: function 'varcharin(opaque)' does not exist

Thanks

Jim