The GHC Team is pleased to announce a new patchlevel release of GHC, 7.8.3.
haddock 2.14.3 that ships with it seems to be quite broken. Perhaps it's a bad interaction with cabal, it's hard to say from the outside, but here are some details.
Here's the kind of error I get from haddock when I try to use cabal to install a package (primitive, in this case):
module ‘primitive-0.5.3.0:Main’ is defined in multiple files: dist/build/tmp-92638/Control/Monad/Primitive.hs