Please read: http://www.mew.org/~kazu/proj/ghc-mod/
Emacs front-end, which is consistent with binaries on Hackage, is available stable MELPA whose URL is http://melpa-stable.milkbox.net/packages/. So, your "~/.emacs" should be:
(require 'package)
(add-to-list 'package-archives
'("melpa" . "http://melpa-stable.milkbox.net/packages/"))
(package-initialize)
With this configuration you can install the stable Emacs front end indicated by "ghc" from MELPA while you can install ghc-mod
/ghc-modi
binaries by:
% cabal update
% cabal install ghc-mod
You should install both Emacs front-end and binaries from this git repo. If you use the snapshot MELPA to install Emacs front-end, you would suffer from inconsistency between Emacs front-end and binaries.