On Tue, Apr 21, 2015 at 5:56 PM Yitzchak Gale <gale@sefer.org> wrote:

Michael Snoyman wrote:
> Can you give an example of a concrete problem you're
> expecting to run into?

Package foo uploads a new version with a critical bug fix.
As is often the case, this new version also supports updated
dependencies, including exceptions. The new exceptions
breaks the old SomeException type, so foo is forced to
specify a lower bound that excludes the old exceptions.

But that's the scenario I'm asking for more information on. Can you clarify what you're describing here? I'm not seeing a situation where an author couldn't easily be compatible with GHC <=7.8 by sticking to the old API?

I depend on foo and I need to compile using GHC 7.8.
Can I get this critical bug fix for foo?

We can't always prevent this kind of scenario.
And when it does happen in an isolated case, there
are work-arounds. But for a ubiquitous dependency
like exceptions, this single breaking change would
effectively block future upgrades of a significant proportion
of Hackage for GHC 7.8.