8.2.1 ghc haskell on FreeBSD, 801 in pkg?

Updating lang/ghc is not easy. You'll also have to update and fix all Haskell ports. See the commit message for GHC 8.0.2 to see what's involved: https://svnweb.freebsd.org/ports?view=revision&revision=447548

The GHC from haskell.org will work fine. We also have the Haskell build tool devel/stack which downloads and manages GHC versions (with a working set of Haskell packages for each version) on its own for your own projects.