Ernest E Vogelsinger <ernest(at)vogelsinger(dot)at> writes:
> So if I get you right the "IS NULL" predicate doesn't fit into "<op>"
> "<value>"?
Exactly.
In the last go-round on this topic, there was some discussion of
changing IS NULL from a specialized construct into an operator
(and underlying function), which'd allow it to be fit into the
index opclass abstraction. I think it's doable, but no one's
got round to doing it yet.
regards, tom lane