Relaxin the PVP with regards to adding instances

[Ian Lynagh]

On Wed, Sep 05, 2012 at 05:43:04PM -0700, Michael Sloan wrote:
> While I suppose it could break
> proper dependency resolution, a big reason for upper bounds is
> preventing a cascade of confusing errors.  With orphan instances the
> errors are very finite.

I don't think the type of errors was a factor in designing the PvP. The
primary (perhaps even only) goal was to design packages in such a way
that if "cabal install foo" would have worked yesterday, then it will
also work today.

That means that if foo depends on bar, and there is a suitable newer
version of bar available today, then foo had better work with that
version too.

The person installing foo isn't interested in developing foo or bar, so
doesn't want any error at all!


Thanks
Ian