while trying to live with different versions of packages, I found cabal-install's behaviour strange because: you can "cabal install" a package without any complaint but the next "ghc-pkg list" is all red because of conflicts. and it's too late then - there's no way to get back. even if you re-install some package, it seems it is getting a different hashcode, so it's not recognized. if you were doing "cabal install --global" for some ghc package (e.g. old-locale), then ghc seems completely hosed and you've got to re-install the compiler. well that's not a big deal by itself but afterwards you have to re-install all packages ... so please please please have "cabal install" fail with some error message if (that is, before) the install would break anything. - J. $ ghc --version The Glorious Glasgow Haskell Compilation System, version 6.12.1 $ cabal --version cabal-install version 0.8.0 using version 1.8.0.2 of the Cabal library