On Wed, Sep 28, 2016 at 2:45 PM, Brandon Allbery
This turns out to be much easier if you assume that Windows and OS X are not worth supporting, or are happy with forcing users on those platforms to jump through annoying hoops (*especially* Windows; there are reasonable ways to get gtk on OS X, even though it doesn't come with the system, but Windows is still the Wild West as far as third party libraries are concerned --- Chocolatey notwithstanding). :/
GTK on Windows is trivial at this point, with stack and LTS 7+. Try it yourself: stack exec -- pacman -S mingw-w64-x86_64-gtk3 stack install gtk2hs-buildtools stack install gtk3 --flag gtk3:build-demos gtk2hs-demo-carsim (I didn't start 100% clean but I don't *think* there are any other pacman packages required...)