Mac OS X Installer Packages
Please use the haskell-platform. See https://www.haskell.org/platform/mac.html for further details.
Alternatively, a self-contained relocatable binary release for Mac OS X, that avoids the need for putting files in /usr/bin, etc, can be found at https://github.com/ghcformacosx/ghc-dot-app. This is probably the least intrusive way of getting a version of GHC onto a Mac at present (mid-2014) and will allow you to build GHC from source (other than the documentation).