This is because a revision to the cabal file was published[1]. Tarballs always stay the same (because of possible signing, etc) but cabal-install will use the revised metadata when doing most of its operation including `install', `get', and `unpack'.

You don't say how you are trying to install mtl, is it not through Cabal? Either way, make sure to use the revised cabal file and it should be fine.

HTH,

Adam

[1] https://hackage.haskell.org/package/mtl-2.2.1/revisions/

On Wed, Feb 10, 2016 at 3:09 PM, Björn Peemöller <bjp@informatik.uni-kiel.de> wrote:

Hi Cafe,

I just wanted to install the mtl package for GHC 8.0.1-rc2, but
installation failed with

Setup: Encountered missing dependencies:
transformers ==0.4.*

Taking a look at the package description [1], it specifies

build-depends: base < 6, transformers >= 0.4 && < 0.6

but the Cabal description in the tarball [2] says

build-depends: base < 6, transformers == 0.4.*

Strangely, if I execute

$ cabal unpack mtl-2.2.1

I obtain a version with the same specification as [1].

Does anybody has an explanation for this?

Regards,
Björn

[1]: http://hackage.haskell.org/package/mtl-2.2.1/mtl.cabal
[2]: http://hackage.haskell.org/package/mtl-2.2.1/mtl-2.2.1.tar.gz
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