Question

I have the Haskell Platform 2012.4.0.0 installed and I’d like to try out the unittyped package.

When I try to install it with cabal-dev -s some-dir install unittyped I’m getting the error:

$ cabal-dev -s some-dir install unittyped
Resolving dependencies...
cabal: Could not resolve dependencies:
trying: unittyped-0.1 (user goal)
next goal: base (dependency of unittyped-0.1)
rejecting: base-3.0.3.2, 3.0.3.1 (global constraint requires installed
instance)
rejecting: base-4.5.1.0/installed-724... (conflict: unittyped => base>=4.6 && <4.7)
rejecting: base-4.6.0.0, 4.5.1.0, 4.5.0.0, 4.4.1.0, 4.4.0.0, 4.3.1.0, 4.3.0.0,
4.2.0.2, 4.2.0.1, 4.2.0.0, 4.1.0.0, 4.0.0.0 (global constraint requires installed instance)

and cabal-dev -s some-dir install base-4.6.0.0 yields a similar message.

Is there a way to get past these errors?

Answer 1

The unittyped package requires GHC >= 7.6, it uses DataKinds (well, DataKinds first appeared in 7.4, but the implementation was not yet complete; maybe unittyped would also work with 7.4) and explicitly depends on base >= 4.6 && < 4.7.

As noted parenthetically above, it might also work with ghc-7.4, to test that

$ cabal unpack unittyped
$ cd unittyped-0.1
-- edit the .cabal file to allow base-4.5.*
-- and bump the version, so that cabal doesn't think it cannot work with base-4.5.*
$ cabal install

That may or may not work.

The safe option is to install ghc-7.6.1, but that would mean dropping the Haskell Platform.