[Nix-dev] override ghc-paths to point to wrapped ghc?

[Peter Simons]

Hi Corey,

you realize that ghc-paths is patched in Nix, right?

  https://github.com/NixOS/nixpkgs/blob/master/pkgs/development/libraries/haskell/ghc-paths/ghc-paths-nix.patch

The library returns whatever paths found in the environment variables

  NIX_GHC
  NIX_GHCPKG
  NIX_GHC_LIBDIR
  NIX_GHC_DOCDIR

if those are set. The 'ghcWithLibraries' even generates wrapper scripts
for standard tools that configure those paths appropriately.

Take care,
Peter