[Haskell-beginners] Haskell Platform on OS X, Sierra

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?