GHCi, version 8.4.3: http://www.haskell.org/ghc/  :? for help
xcrun: error: active developer path ("/Applications/Xcode.app/Contents/Developer") does not exist
Use `sudo xcode-select --switch path/to/Xcode.app` to specify the Xcode that you wish to use for command line developer tools, or use `xcode-select --install` to install the standalone command line developer tools.
See `man xcode-select` for more details.
`clang' failed in phase `gcc'. (Exit code: 1)

GHCi, version 8.4.3: http://www.haskell.org/ghc/  :? for help
xcrun: error: active developer path ("/Applications/Xcode.app/Contents/Developer") does not exist
Use `sudo xcode-select --switch path/to/Xcode.app` to specify the Xcode that you wish to use for command line developer tools, or use `xcode-select --install` to install the standalone command line developer tools.
See `man xcode-select` for more details.
`clang' failed in phase `gcc'. (Exit code: 1)

sudo xcode-select -switch /Library/Developer/CommandLineTools

sudo xcode-select -switch /Library/Developer/CommandLineTools