Proposed resolution:

In section [propagation] insert a new paragraph between p.5 and p.6:

An object e of type exception_ptr can be contextually converted to bool. The effect shall be as if e != exception_ptr() had been evaluated in place of e. There shall be no implicit conversion to arithmetic type, to enumeration type or to pointer type.

Rationale:

Solved by N3073.

[ 2010-03-14 Howard adds: ]

We moved N3073 to the formal motions page in Pittsburgh which should obsolete this issue. I've moved this issue to NAD Editorial, solved by N3073.

[ 2009 Santa Cruz: ]

Move to Ready. Note to editor: considering putting in a cross-reference to [conv], paragraph 3, which defines the phrase "contextually converted to bool".

As of N2857 [propagation] p.5, the implementation-defined type exception_ptr does provide the following ways to check whether it is a null value:

void f(std::exception_ptr p) {
  p == nullptr;
  p == 0;
  p == exception_ptr();
}

This is rather cumbersome way of checking for the null value and I suggest to require support for evaluation in a boolean context like so:

void g(std::exception_ptr p) {
  if (p) {}
  !p;
}