I have Ubuntu 14.04LTS. I downloaded the latest ghc-7.8.3
from http://www.haskell.org/ghc/download_ghc_7_8_3#x86_64linux and installed it to /usr/local
I remember having a similar issue when setting up ghc-7.8. It has something to do with the new cabal, which somehow isn't compatible with libraries installed with an older versio (but it fails to give the correct problem reason.
Anyway, I think reinstalling the packages in question
cabal install random --reinstall --force-reinstalls
sets it up so cabal install tf-random
should then succeed.