First: Yes, I really do mean to install install just GHC, and not the Haskell Platform. I am installing in a VM made just for this purpose, I have the platform installed elsewhere.
So the standard instructions for installing from a distro mentions ghc6 which is not recognized as a valid target (anymore?). So if I install the ghc package instead, I (successfully) get 7.6.3.
I did make sure that I have universe enabled, and have the latest package list. Is it that 7.8.2 is not packaged yet?
The officially supported version (in other words, the version in the official repos) is 7.6.2 for 13.04 and 7.6.3 for 13.10 and 14.04, according to this website.
If you wish to use a different version, you can compile it from source or use a PPA that supplies the one you prefer, for example, check out this PPA. (For more information on PPAs, see this question.)