ghc-mod is a backend program to enrich Haskell programming in editors. It strives to offer most of the features one has come to expect from modern IDEs in any editor. ghc-mod provides a library for other haskell programs to use as well as a standalone program for easy editor integration. All of the fundamental functionality of the frontend program can be accessed through the library however many implementation details are hidden and if you want to significantly extend ghc-mod you should submit these changes upstream instead of implementing them on top of the library. For more information, please see its home page.