[Haskell-beginners] Cabal problems - as usual..

Gregory Guthrie guthrie at mum.edu
Fri Jan 30 13:54:36 UTC 2015

I have a very basic usage pattern and installation on a few machines, and yet continually run into the often discussed cabal-maze of problems on all of them.

I have read all of the many explanations of why it is a hard problem, but so far the only solution I have heard for repair is to erase the installed library files, and start over. This can be hard if one has any external libraries installed which were themselves a lot of work to get functioning, an example are graphics libraries (like WxWin).

Has anyone created any scripts which would note everything which is installed, clear out all libraries, and then try to re-install everything? (This is on Windows....) Or would this typically just run into the same problems?

Doing a cabal update, it notes a new version of cabal -install, so trying that fails, and now it looks like cabal itself is broken (no installs work).
Any short-term \remedies, and/or long term better approaches?

>cabal update
Downloading the latest package list from hackage.haskell.org
Skipping download: Local and remote files match.
Note: there is a new version of cabal-install available.
To upgrade, run: cabal install cabal-install

>cabal install cabal-install
Resolving dependencies...
cabal: Could not resolve dependencies:
trying: Cabal- (user goal)
trying: ghc-syb-utils-0.2.3/installed-f83... (user goal)
next goal: ghc (dependency of ghc-syb-utils-0.2.3/installed-f83...)
rejecting: ghc-7.8.3/installed-a4e... (conflict:
Cabal==, ghc => Cabal==
rejecting: ghc-7.4.2/installed-4d6... (conflict: ghc-syb-utils => ghc==7.8.3/installed-a4e...)
Backjump limit reached (change with --max-backjumps).

Note: when using a sandbox, all packages are required to have consistent
dependencies. Try reinstalling/unregistering the offending packages or
recreating the sandbox.

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