$ yaourt --aur -S haskell-hexpat
Also now available, a new package: hexpat-pickle: XML picklers based on hexpat, almost source code compatible with HXT.
This package allows Haskell data structures to be pickled to/from the Tree datatype defined in the hexpat package. It is almost source code compatible with the pickling functionality of the HXT package, to allow you to switch easily between the two implementations.
You can get haskell-hexpat-pickle for Arch here.