Hi, I wrote a simple shell function for switching GHC version on the system. It works only under Mac OSX, and only switch GHCs installed via .pkg installers. It's useful to experiment newer features without worrying breaking environment. GHC_BASE_DIR=/Library/Frameworks/GHC.framework/Versions/ ghcs () { VERSION=$1 sudo $GHC_BASE_DIR/$VERSION/Tools/create-links . /Library/Frameworks / } Usage: ~/work/today 08:21 ghcs 7.4.0.20111219-x86_64 Password: ~/work/today 08:21 ghc --version The Glorious Glasgow Haskell Compilation System, version 7.4.0.20111219 ~/work/today 08:21 ghcs 7.4.1-x86_64 ~/work/today 08:22 ghc --version The Glorious Glasgow Haskell Compilation System, version 7.4.1 Now I'm curious of better way to achieve this. This have limitations described above. Even it requires sudo because it modified symbolic links under `/usr`. Suggestions? -nwn