[Haskell-cafe] Again, version conflicting problem with cabal-install

Magicloud Magiclouds magicloud.magiclouds at gmail.com
Tue Jun 19 11:39:00 CEST 2012

And today I met another situation, which I think solvable by computer.

Hackage A depends on magicloud (any) and container (, and
hackage magicloud depends on container (any).
Now I've installed magicloud, using container Then I failed
to install A, with any solver.

So the solvers are using the status that is installed, not the
definitions from original hackages?

On Wed, May 2, 2012 at 2:47 PM, Magicloud Magiclouds
<magicloud.magiclouds at gmail.com> wrote:
> Hi, long time no see.
> I am using cabal-install-0.15.0. And the new solver. It sure solves
> some problem. Thanks for the work.
> Well, on the other hand, there still are hackages that I just have no
> idea how the author make it (probably not up-to-date hackage
> database). After human-solver checking, these hackages are not be able
> to build at all under certain conditions.
> So, I am voting on the "force-allow" flag.
> On Sat, Feb 4, 2012 at 12:36 AM, Andres Löh <andres.loeh at googlemail.com> wrote:
>> Hi.
>>>>  --force-allow=foo-1.3
>>>> with the semantics that all dependencies on foo will be changed to
>>>> allow foo-1.3 to be chosen. Would that be ok? Other suggestions?
>>> Can't this be integrated with the current --constraint flag?
>> It could be, but ...
>>> If the
>>> constraint is able to be satisfied without unrestricting any bounds,
>>> fine.  Otherwise, unrestrict any bounds on that constraint.  What
>>> would be the drawbacks?
>> ... it shouldn't happen automatically. There are perfectly valid and
>> safe reasons to use --constraint, whereas this new feature is
>> inherently unsafe. But allowing general constraint syntax and calling
>> the flag something with "constraint" in it is perhaps a good idea.
>>> An advantage is being able to specify --constraint='foo >= 1.3' to get
>>> foo- instead of having to find out exactly which version you
>>> want.  And if you already know what you want, you may always say
>>> --constraint='foo =='.
>> Yes.
>>> Looking forward to the new solver! =)
>> I need testers and feedback. You can already use it. It's in the
>> cabal-install development version, and can be enabled by saying
>> --solver=modular on the command line.
>> Cheers,
>>  Andres
> --
> 竹密岂妨流水过
> 山高哪阻野云飞
> And for G+, please use magiclouds#gmail.com.


And for G+, please use magiclouds#gmail.com.

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