Markus Schaber <schabi(at)logix-tt(dot)com> writes:
> This lead me to the question whether it is possible to use "internal" as
> state type for an Aggregate whose functions are implemented in C.
No, because the system has no idea what the representation of an
"internal" state value might be, and in particular how to copy it.
The same goes for other pseudotypes.
regards, tom lane