The release 7.8.3 bindist for OS X was flawed: It was not build SplitObjs. That is my fault for not catching it before releasing it. You may demand a beer from me at ICFP as restitution.... I have built a new 7.8.3 bindist for OS X, and tested in 10.9, 10.7, and 10.6(!). It is SplitObjs, and still performs better than the gcc based build. Find it here: ghc-7.8.3-x86_64-apple-darwin-r2.tar.bz2 http://www.ozonehouse.com/mark/platform/ghc-7.8.3-x86_64-apple-darwin-r2.tar... shasum -a 256: 7f056a48de5158a950e49f208d1e79c6721c2a908db55f7691f7695171c63306 Updated blurb for the release page: This is a bindist for Mac OS X, 10.6 or later. The package requires the command line tools package of Xcode 4 or XCode 5 to be installed. You can find Xcode at http://developer.apple.com/. If you are installing on a gcc based system (gcc --version doesn't not include the word "clang"), then then when installing this, use the command make install CC_CLANG_BACKEND=0). - Mark