[Haskell-cafe] How to determine correct dependency versions for a library?

[Johan Tibell]

On Mon, Nov 12, 2012 at 1:06 AM, Erik Hesselink <hesselink at gmail.com> wrote:

> tl;dr: Breakages without upper bounds are annoying and hard to solve for
> package consumers. With upper bounds, and especially with sandboxes,
> breakage is almost non-existent.
>
> I don't see how things break with upper bounds, at least in the presence
> of sandboxes. If all packages involved follow the PVP, a build that worked
> once, will always work. Cabal 0.10 and older had problems here, but 0.14
> and later will always find a solution to the dependencies if there is one
> (if you set max-backjumps high enough).
>

The "breakage" people are talking about with regards to upper bounds is
that every time a new version of a dependency comes out, packages with
upper bounds can't compile with it, even if they would without the upper
bound. For example, the version number of base is bumped with almost every
GHC release, yet almost no packages would actually break to the changes
that caused that major version number to go up.
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