Support transformers-0.6

[andreasabel]

Please support transfomers-0.6.
Atm, attempting to constrain to it gives these compilation errors:

Building library for free-5.1.7.. 
...
[ 9 of 20] Compiling Control.Monad.Free.Class ( src/Control/Monad/Free/Class.hs, dist/build/Control/Monad/Free/Class.o, dist/build/Control/Monad/Free/Class.dyn_o )

src/Control/Monad/Free/Class.hs:44:1: error:
    Could not load module ‘Control.Monad.Trans.List’ 

src/Control/Monad/Free/Class.hs:45:1: error:
    Could not load module ‘Control.Monad.Trans.Error’ 

[RyanGlScott]

At the moment, this is waiting on a new release of mtl that supports transformers-0.6. Since it appears that a new mtl release may be happening soon, I'll wait to see how that shakes out. In the meantime, I have an experimental mtl-2.3 branch that will likely serve your needs in the interim.

[emilypi]

Just to bump this, mtl-2.3 has been released, and free looks good to go to bump the dep:

  -- GHC-7.8 bundles transformers-0.3,
  -- mtl-2.2.* requires transformers >=0.4
  -- mtl-2.3.* requires base >=4.12
  if impl(ghc >=7.10)
    build-depends:
      mtl               >= 2.2.2 && < 2.4

This builds fine on my machine

[RyanGlScott]

Thanks! I've uploaded free-5.1.8 to Hackage with a fix.