[arch-haskell] Adding another data file for dependency "hints"

[Rémy Oudompheng]

On 2010/12/30 Magnus Therning <magnus at therning.org> wrote:
> On Tue, Dec 28, 2010 at 09:08, Rémy Oudompheng <remyoudompheng at gmail.com> wrote:
>> Hello,
>>
>> Since pacman's dependency specification is much less powerful than in
>> Cabal, cabal2arch may output wrong version constraints while trying to
>> approximate the true specified dependencies. I prefer this to dropping
>> all version requirements when they cannot be expressed in the pacman's
>> way.
>
> This sounds reasonable.  However, do you have examples of dependencies
> that CABAL can express but pacman can't?  (I was under the impression
> that the difference was that CABAL allowed more terse expressions, not
> that it allowed more.)

See the issue reported by
https://github.com/archhaskell/cabal2arch/issues#issue/19. PKGBUILDs
can only specify dependency requirements with one inequality (<, >, <=
or >=) whereas Cabal can specify any Boolean combination of
inequalities.

>> In order to get improved PKGBUILDs I thought we could have a better
>> usage of the dependency resolution capabilities in the Cabal library,
>> this is summed up in this commit
>>
>>  http://github.com/remyoudompheng/archhaskell/commit/2e614b2
>>
>> This adds an extra file, platform-provides.txt, that lists our
>> preferred versions for various packages. For the moment I have filled
>> it with the contents of Haskell Platform.
>
> Is it worth considering downloading this file dynamically, rather than
> compiling it into the executable statically?

It's been some time since these lists were not compiled in the
executable. I have added a flag to cabal2arch (in my copy
http://github.com/remyoudompheng/cabal2arch) to handle a custom
directory or URL where these files could be stored. I am using mtl for
error handling.

Regards,
-- 
Rémy.