Historically ghc-mod provided (and still does) support for emacs and vim as part of its distribution.
It is also used by a number of other IDE backends to provide a way of getting information about a project without worrying
too much about the details of how the project is organised on the file
system.
There is currently a discussion between various interested parties about adjusting the way ghc-mod communicates with the IDE, to make it simpler to provide this support for other environments.
This should end up with a definition of a protocol that ghc-mod can expose, which should also allow tools (such as HaRe) to be plugged into it, so that IDE integration can be handled by the various IDE integrators in a clean, common way.
This is all just hand waving at the moment, so if anyone would like to get involved I am proposing that we revive the "Haskell IDE implementation"[1] google group/mailing list to host the discussion.