Tom Lane wrote:
We can ask the user to provide a prior() and next() function, and if
they aren't provided, we assume it's continuous.
Well, that still leaves us with the problem that Joe Schmo will file
a bug when "create function next(float4) returns float4 as
$$ select $1 + 0.00001 $$" doesn't behave sanely for him. I'd prefer
not to leave it to the user to decide whether a type is discrete or
not. The traffic on pgsql-bugs is convincing evidence that a very
large fraction of our user-base doesn't understand that floats are
inexact :-(
Indeed.
I think "countable" is a more accurate word than "discrete". Strings are
discrete but not countable.
It's been too long since college math classes for me to be sure whether
"discrete" is really the exact term here. But I'm even more suspicious
of "countable". I think a suitable diagonalization argument might show
that strings are countable. That's getting a bit off-topic though...
Right, I don't think strings are any more or less countable than
integers. (and yes, it's a bit OT).
Surely the issue from our POV is whether, given two distinct members of
a class, we can ever say there is not any intervening member of the
class according to some ordering. If we can't then next() and prior()
make no sense for that class.
cheers
andrew
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