Perhaps the developers want to take a look at this distribution.It is reported that is written in a `purely functional package management' and tries to be a highly safe OS, where `upgrading a system is as reliable as reinstalling from scratch'. http://nixos.org/nixos/
Because the files of a new configuration don’t overwrite old ones, you can (atomically) roll back to a previous configuration. For instance, if after a nixos-rebuild switch you discover that you don’t like the new configuration, you can just go back
It can be an inspiration for a new version of pacman rewritten in haskell? Also Don Stewart's talk about 'Scripting with Types' might inspire someone too (BTW since he started arch-haskell I think he is a Arch user): http://donsbot.files.wordpress.com/2009/01/semicolon.pdf