Hi Cafe!

I have program written in Haskell and Swift that runs on Mac. This program uses some features that was introduced in last version of OS X “Yosemite” 10.10, but some of my users use previous version "Maverics " 10.9. Is there some technique that allows me to extend my cabal file and specify which *version* of os is currently in use and don't load some of modules?

AFAIK, Cabal's `conditional` doesn't provide such mechanism, but something like

```
if os(osx) && ver(=10.10)
if os(osx) && ver(<=10.9)

```
will be nice.

Maybe there is other approach to this problem?I don't want to use `CPP` extension to handle this within code.

Thanks