On Sun, Feb 26, 2012 at 6:44 PM, A.M. <agentm@themactionfaction.com> wrote:
> If you are willing to go full length, then the computer science term is "referential transparency", no?
>
> http://en.wikipedia.org/wiki/Referential_transparency_(computer_science)
>
> So a function could be described as "REFERENTIALLY TRANSPARENT".
Hmm, I think that's very close to what we're looking for. It might be
slightly stronger, in that it could conceivably be OK for a leakproof
function to read, but not modify, global variables... but I can't
think of any particular reason why we'd want to allow that case.
OTOH, it seems to imply that referential transparency is a property of
expressions built from pure functions, and since what we're labeling
here are functions, that brings us right back to PURE.
I'm thinking we should go with PURE. I still can't think of any real
use case for pushing down anything other than an immutable function,
and I think that immutable + no-side-effects = pure.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
