[Haskell-cafe] Re: Why cabal forces reinstallation of happstack-utils?

[Maciej Piechotka]

On Wed, 2010-05-05 at 02:17 +0200, Daniel Fischer wrote:
> On Wednesday 05 May 2010 01:45:29, Maciej Piechotka wrote:
> >
> > I updated local copy, as shown, but cabal wants to rebuild it anyway. My
> > question was rather why the repo is considered at all when the package
> > is installed.
> >
> > Regards
> 
> Okay, I didn't quite understand your question, sorry.
> So, what's the situation?
> You unpacked happstack-util, edited the cabal file to allow parsec-3.1, 
> cd'ed to the unpacked directory and ran cabal install there, so you had 
> happstack-util installed.
> Then you ran cabal install --dry-run and it said
> Resolving dependencies...
> cabal: cannot configure happstack-util-0.5.0.
> 
> Is that correct?
> 

No.
1. I downloaded happstack-utile[1]
2. Edited cabal file
3. Installed it successfully linking with parsec 3.1
4. I tried to run cabal install happstack --constraint 'parsec >= 3'
5. It complains that happstack-utile needs to be installed against
parsec 2 

If I just run:
% runhaskell Setup.hs configure --user
All seems to be ok but
% cabal install
Wants to reinstall packages (or complains about constraints).

> I don't know why cabal does that.
> As a guess: it looks at the .cabal file in the package index to find out 
> what's needed, compares with the output of ghc-pkg list, finds a missing 
> dependency (parsec-2.*) and decides to reinstall.

It is not a missing dependency. It is that the cabal-install tries to
use dependencies from hackage instead of installed packages.

Regards

[1] Now it is HStringTemplate but problem is the same
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