[Haskell-cafe] How to keep cabal and ghci package versions in sync?

[Rogan Creswick]

On Sun, Apr 24, 2011 at 11:13 AM, Gracjan Polak <gracjanpolak at gmail.com> wrote:
> I have a project with a .cabal file listing package dependencies using
> the usual version constraints ==X.Y.* <Z.W or >=K.J syntax.
> Standard route cabal configure; cabal build works correctly as it is able
> to select working set of package versions.
>
> I have also a .ghci file. When I run GHCi it uses all latest installed packages
> in the system. This prevents the project from loading.
>
> I tried to use 'cabal-dev ghci', but this still selects latest global packages.

This should only arise for the base ghc packages, which are tied
closely enough to ghc that you should probably switch ghc versions if
you want to work with different versions of those core packages.

If you're installing additional packages globally, my only advice is:
Beware, there be dragons!  I strongly recommend that you ghc-pkg
unregister all the non-essential packages from your global package db
because:

 (1) cabal-dev will not bring you any benefit.
 (2) you will eventually run into ugly unsatisfiable dependency issues
between your local and global package databases.
 (3) you may inadvertently cause a base package to be upgraded, which
is somewhat easier to fix if it's installed to a local package db.

cabal-dev ghci should be able to do what you want, but it has no
control over the global db.  I'd be happy to send you a list of the
packages that ghc comes with, if you choose to unregister packages
from the global db (assuming you're using one of the OS/arch/ghc
combinations I have available :)

--Rogan

>
> So, how to I load up ghci with the same package versions as selected by cabal?
>
> Thanks!
>
> --
> Gracjan
>
>
>
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