Haskell-Source with Extensions (HSE, haskell-src-exts) is an extension of
the standard haskell-src package, and handles most registered syntactic
extensions to Haskell, including:

  * Multi-parameter type classes with functional dependencies
  * Indexed type families (including associated types)
  * Empty data declarations
  * GADTs
  * Implicit parameters
  * Template Haskell

and a few more. All extensions implemented in GHC are supported.
Apart from these standard extensions, it also handles regular patterns as
per the HaRP extension as well as HSX-style embedded XML syntax.

WWW: https://github.com/haskell-suite/haskell-src-exts