Among other features [stack](https://github.com/commercialhaskell/stack/) provides a clean and deep dependency management system that even takes care of installing toolchain (ghc, alex, happy, cabal...) in a segregated environment. Building remote propellor with stack would remove the limitation that code should be compilable with stock ghc from package manager. I have done some preliminary work on this feature in my [github clone](https://github.com/abailly/propellor) for propellor, currently from 2.17.2 branch (I wanted to reuse existing properties). The code is mostly in [Bootstrap](https://github.com/abailly/propellor/blob/master/src/Propellor/Bootstrap.hs) and is currently limited to linux systems. Adapting to FreeBsd should be straightforward as this is supported by slack and there are native builds available. 

If there is interest in such a feature I would be happy to move it to HEAD and provide a patch.
