Hackage now has 1540 (+97) Haskell packages, of which 1342 (+76) (87.2%) have been natively packaged for Arch in AUR. All these packages are available via AUR, using the “yaourt” tool.
You can find the status of all Haskell packages in Arch here, regularly updated using the archlinux Haskell package tools.
Arch Linux and Haskell 