Hey everyone, if you are actively using ghc 7.6 on your mac, for now please do not install xcode 5. It will break your ghc install, because 7.6 doesn't know how to correctly use Clang for the CPP work. (ghc head / and thus 7.8 will work fine with xcode 5, thanks to some outstanding work by Austin Seipp, 7.6 does not) if you do not need xcode 5, and you're actively using ghc 7.6, stay with xcode 4.6 for now. if you installed xcode 5 because its there, and now your ghc 7.6 is occasionally giving you strange errors involving CPP parse failures on fragments like "#-}", you should go to the apple developers website, download, and reinstall the xcode 4.6 CLI tools. if you need both xcode 5 and ghc in working order *right now, tomorrow*, either a) live on the wildside: test out using ghc head: also means you could play with ghc-ios too! b) if you need both in working order now, and stabilish, Darin Morrison has a set of mac-homebrew taps that should be you use https://github.com/darinmorrison/homebrew-haskell these taps should be regarded as more "official" and "canonical" than the formula's that brew provides (the normal brew ones recurrently have problems induced by folks who aren't haskell devs) c) wait a wee bit till 7.8 lands in all its glory, and have both the freshest of xcodes, and the newest of awesome ghcs tl;dr if you don't need xcode 5, having xcode 4.6 CLI tools installed will stand you in good stead. if you are on os x mavericks, or absolutely need xcode 5 installed, and you want a ghc thats already released, use darin's brew formulae https://github.com/darinmorrison/homebrew-haskell Darin and I plan to spend some time next month preparing an unofficial patched version of ghc 7.6 that should play nice with clang / xcode 5, though at such a time ghc 7.8 will be in RC status at the very least. cheers -Carter