On Wed, Sep 15, 2010 at 7:47 PM, Peter Schmitz
Not that I'm having any problem with parsec 2.1.0.1, but I guess I would like to install the latest (3.1.0), unless there is a reason not to.
I can't seem to get Cabal to do so; thanks in advance for any help.
I don't understand part of the output from "cabal install --dry-run --reinstall -v parsec" at the end below, which includes: "selecting parsec-2.1.0.1 (hackage) and discarding parsec-2.0, 2.1.0.0, 3.0.0, 3.0.1 and 3.1.0".
(http://hackage.haskell.org/package/parsec seems to point to 3.1.0.)
I consider this a misfeature of cabal-install. Cabal-install will check here: http://hackage.haskell.org/packages/archive/preferred-versions Before deciding out how to handle an 'install' request. You'll notice that it says: parsec < 3 Sadly cabal-install doesn't warn you or ask what version you want. There is an unwritten policy that cabal knows better than you do about what packages you want. And then it silently enforces it's point of view on you unless you specify a conflicting constraint. And unless the package is base, in which case it only listens if you either a) give an upper bound on base, or b) provide a preference (instead of a constaint). You can work around these (broken) global policies by editing your local cabal config. Should be in $HOME/.cabal/config (or the similar place on windows). You can add a line like: preference: base >= 4, parsec >= 3 That should help to nullify the global policy. Cabal bugs not withstanding, this comes about because cabal is not a package manager. Unlike distributions like Debian there is no way to subscribe to 'stable', 'experimental', or 'developer only' package classifications. Unfortunately, the current 'solution' has been to enforce a 'one size fits all' policy on users with an essentially undocumented way to override it (which has to be applied for each cabal-install installation). I assume this strategy was picked because it was easy to implement and developer time can be scarce. Jason