Proposal: Add exception info

[Yitzchak Gale]

Michael Snoyman wrote:
> Sorry to confuse this thread with a second Michael.
>
> 1) there's a very good use case that's currently excluded by the
> API, and (2) Michael Sloan figured out some great ways to minimize the
> breakage. You could even argue that this proposal has *no* API breakage.

Perhaps I missed it, but wouldn't this create major breakage
across hackage for 7.8 and before?

We will certainly be using 7.8 for years to come, at least for
older versions of our products that we must continue to
support. In fact, we are only now able to reduce
our use of 7.6 to a fairly low (but non-zero) level.

This cycle will likely be even longer than usual for the
7.10 upgrade due to the inclusion of the FTP breaking
changes which make upgrading much more difficult.

I certainly hope that most of the ecosystem will continue
to support GHC versions going back at least one or two
major versions, as it always has in the past.

All that said, I am in favor of this change - it is a great
design. But I would strongly oppose doing it immediately
unless there is some plan to allow continued support
of recent pre-7.10 GHC versions in the ecosystem.

Thanks,
Yitz ("you can call me Michael")