I tend to disagree with this. Yes, GHC is a large application and most certainly developed by experts, but it's also a project with a very long history, whilst Haskell (language, extension, conventions,...) have changed over the years, and this shows in several places.
Next to that, GHC code isn't very idiomatic at times (e.g. for performance reasons, or because it can't depend on too many external high-level libraries).
