Vesa Kaihlavirta has moved GHC 6.10 from [testing] into [extra], so Arch now ships with GHC 6.10 out of the box. Also out of the box comes:
So you can immediately get into full haskell development mode.
The AUR package suite has been updated to play well with 6.10, and the most used AUR packages will continue to move into the binary packaging of the [community] repository.
The AUR packages have an advantage over cabal-install of having C libraries resolved to native packages, and they’ve been checked to build on Arch.