I'd guess that you've got an older version of cabal-install on your system that doesn't support GHC 8. You can test that with `cabal --version` and see if it's 1.24 or later.

My recommendation would be to try out Stack. There are new easier installation instructions at https://haskell-lang.org/get-started, and recent Stackage Nightly snapshots are all using GHC 8.0.1.

On Mon, Jul 11, 2016 at 10:49 AM, Magicloud Magiclouds <magicloud.magiclouds@gmail.com> wrote:

Hi,
I update my GHC to 8.0.1 and failed to install any packages since then.
If I use cabal, I got 'installed package info from too old version of Cabal (key field does not match id field)' for every package.
If I use Setup.hs, I got 'Configuring Cabal-1.24.0.0...
Setup.hs: ghc-pkg dump failed'.
What should I do? Googling did not get me an answer.

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