On Sun, Sep 15, 2019 at 09:34:08PM -0400, John Cowan wrote:
> One of the other things that makes SQLite different is the ability to
> define scalar and aggregate functions, as well as collations, on the fly.

I'd say treat it as an extension.  This is so different from the typical
client/server database that it doesn't make much sense to standardise in
the API.

Similar for LISTEN/NOTIFY in Postgres, as a random example which also
involves callbacks.

Cheers,
Peter