[Haskell-cafe] Platform Versioning Policy: upper bounds are not our friends

[Iavor Diatchki]

Hello,

I also completely agree with Bryan's point which is why I usually don't add
upper bounds on the dependencies of the packages that I maintain---I find
that the large majority of updates to libraries tend to be backward
compatible, so being optimistic seems like a good idea.

By the way, something I encounter quite often is a situation where two
packages both build on Hacakge just fine, but are not compatible with each
other.  Usually it goes like this:

  1. Package A requires library X >= V  (typically, because it needs a bug
fix or a new feature).
  2. Package B requires library X < V (typically, because someone added a
conservative upper bound that needs to be updated).

Trying to use A and B together leads to failure, which is usually resolved
by having to install B manually, and remove it's upper bound by hand.  This
is rather unfortunate, because not only it's inconvenient but, also, now
there is no released version of package B that you can explicitly depend on.

-Iavor



On Mon, Aug 20, 2012 at 7:11 AM, Brent Yorgey <byorgey at seas.upenn.edu>wrote:

> On Thu, Aug 16, 2012 at 06:07:06PM -0400, Joey Adams wrote:
> > On Wed, Aug 15, 2012 at 3:38 PM, Bryan O'Sullivan <bos at serpentine.com>
> wrote:
> > > I propose that the sense of the recommendation around upper bounds in
> the
> > > PVP be reversed: upper bounds should be specified only when there is a
> known
> > > problem with a new version of a depended-upon package.
> >
> > I, too, agree.  Here is my assortment of thoughts on the matter.
> >
> > Here's some bad news: with cabal 1.14 (released with Haskell Platform
> > 2012.2), cabal init defaults to bounds like these:
> >
> >       build-depends:       base ==4.5.*, bytestring ==0.9.*,
> >       http-types ==0.6.*
>
> I'm not sure why you think this is "bad news".  I designed this to
> conform exactly to the current PVP.  If the PVP is changed then I will
> update cabal init to match.
>
> -Brent
>
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