Hi, I did a test build [1] of the current ghc-7.8 branch for Fedora 21 devel, which I think should also install to Fedora 20.
I put the packages for x86_64, i386 and armv7hl into the yum repos under http://repos.fedorapeople.org/repos/petersen/ghc-7.7/
I haven't tested this latest build yet but wanted to announce its availability. Let me know if you hit any packaging problems with it.
Jens
ps I also upload the ghc-7.8.0.20140201 src tarball to http://petersen.fedorapeople.org/ghc/ if you want to use to build yourself.
pps Next time I will build it in copr.fedoraproject.org which creates yum repos for one (like OBS).
[1] http://koji.fedoraproject.org/koji/taskinfo?taskID=6483032