On Sun, Jun 12, 2011 at 7:12 PM, Antoine Latter <aslatter@gmail.com> wrote:

Types from differing versions of the same module are specifically not
compatible - even if they are defined identically (in this case they
are different, though).

You can do one of two things:

1. Edit the package description of the package that wants the older
version of parsec to allow to use the new one. Also, it helps to
slightly bump the version number of the package when you do this.

2. Use the older version of parsec in your software. You already have
it installed (or else the package you want to use wouldn't be able to
load!). If you're using ghci you can start it with the option
'-package parsec-2.1.0.1'.

I understand that types from different versions of a module are incompatible. What I don't understand is why one module is using a new version of Parsec when it is constrained to use the "old" one (I control both modules. Their package descriptions contain the same line). Is this a cabal-dev bug?