[Haskell-cafe] Cabal failures...

Johan Tibell johan.tibell at gmail.com
Mon Nov 19 22:38:52 CET 2012

Hi Greg,

On Mon, Nov 19, 2012 at 1:25 PM, Gregory Guthrie <guthrie at mum.edu> wrote:

> I follow the Cabal-messes threads with some interest, since that is the
> hardest area for me since starting to use Haskell. Probably 40-60% of all
> package install fail for some mysterious reason, with threats that trying
>  to fix them will break more things, which generally is true. :-)

We're working on it. Be brave, things are going to get better!

> I am not exert in the area, but I wonder how /why/ this is different than
> other package managers, like apt in Linux, I have never had any problems
> with it, and I would think that their dependencies are of at least similar
> complexities.

The Linux package managers solve a different problems. They let you install
a set of packages that have been manually curated and are know to work
together (i.e. all version dependencies are fixed) while cabal does version
resolution on packages that might not ever have been tried together. If you
install Haskell packages via your distro's package manager I assume they
will always install cleanly. The problem is that people want the latest
bleeding edge of packages, which haven't made it into the distros yet, and
hence they get to experience some of the pains associated with being on the
bleeding edge. Being on Windows also makes things harder, as most
developers don't have a Windows box to test their stuff on.

> In any case; Trying to do a cabal update" I was told to try to update
> "cabal-install", which I think means actually updating cabal (since I
> actually run installs via cabal install...), but that fails with this
> message below, and I don't know how to proceed.

cabal-install is the package that includes the "cabal" executable. Cabal
(with a capital C) is the library that cabal-install uses. The naming is
unfortunate but hard to change at this point. To update cabal-install you

$ cabal update && cabal install cabal-install

Make sure that the place that the "cabal" binary gets installed into (which
is printed at the end of the install) is on your PATH.

> Linking
> C:\Users\guthrie\AppData\Local\Temp\Cabal-\Cabal-\dist\setup\setup.exe
> ...
> Configuring Cabal-
> Warning: This package indirectly depends on multiple versions of the same
> package. This is highly likely to cause a compile failure.

This is a sure sign that things are not going to work well. Could you
include the output of

cabal install -v cabal-install

please. The output here is not enough to tell me what's going on. Please
also include the output of

cabal --version
ghc --version

Are you using the Haskell Platform, if so, which version?

-- Johan
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