I have been running the Haskell Platform on OS X El Capitan for a few months. I just upgraded to Sierra and I notice it broke something. For instance when I run ghci I get 

xcrun: error: invalid active developer path ... missing xcrun ....

What's the best way to recover?  Should I uninstall and reinstall Haskell Platform?

BTW, how DO you uninstall the Haskell Platform on OS X?