Trying to install semigroupoids using transformers-0.2.2.0 and GHC 7.2.2 I get the following error message:
Preprocessing library semigroupoids-3.1...
[ 1 of 12] Compiling Data.Traversable.Instances ( src/Data/Traversable/Instances.hs, dist/build/Data/Traversable/Instances.o )
[ 2 of 12] Compiling Data.Functor.Extend ( src/Data/Functor/Extend.hs, dist/build/Data/Functor/Extend.o )
transformers-0.2.2.0:Control.Monad.Trans.Identity can't be safely imported! The module itself isn't safe.
Failed to install semigroupoids-3.1
It seems to be the same issue like ekmett/contravariant#4 .
We should at least mark the versions so it doesn't try to build there.
This is resolved in HEAD. We'll no longer try to build on GHC < 7.6.