Resolving dependencies...
cabal: Could not resolve dependencies:
trying: Cabal-1.20.0.2/installed-f63... (user goal)
trying: doctest-discover-configurator-0.1.0.6 (user goal)
trying: doctest-0.9.11.1 (dependency of doctest-discover-configurator-0.1.0.6)
next goal: ghc (dependency of doctest-0.9.11.1)
rejecting: ghc-7.8.3/installed-1e7... (conflict:
Cabal==1.20.0.2/installed-f63..., ghc => Cabal==1.18.1.3/installed-445...)
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.