Hi Vasili,
Your problem looks like Cabal hell [1]. The solution to that is to
clear the package database and start over, which should be as simple
as
rm -r ~/.ghc
As long as you haven't installed packages globally (sudo cabal
install) that should be enough.
On Wed, Nov 5, 2014 at 8:21 PM, Michael Snoyman
I'd recommend using Herbert's PPA for installing GHC so you get something newer. bitemyapp has a good guide[1]. I'd also recommend following the Stackage installation guide[2], which builds on top of bitemyapp's guide.
[1] https://github.com/bitemyapp/learnhaskell#getting-started [2] https://github.com/fpco/stackage/wiki/Preparing-your-system-to-use-Stackage
I second this. Haskell development moves quickly, so it's important to have (relatively) recent tools. Once you have Cabal 1.20 installed, I recommend reading up on package sandboxes too [2]. They can make these version conflicts easier to deal with in the future. Chris [1] http://cdsmith.wordpress.com/2011/01/17/the-butterfly-effect-in-cabal/ [2] http://coldwa.st/e/blog/2013-08-20-Cabal-sandbox.html