anchor.diff:    buildInputs = [
       cabal
       ghc
  +    sqitch
     ];
     shellHook = "eval $(egrep ^export ${ghc}/bin/ghc)";
   }
  
positive.code:     hlint
      tasty
      tasty-hunit
    ]);
  in
  pkgs.stdenv.mkDerivation {
  
negative.code: { nixpkgs ? import <nixpkgs> {}, compiler ? "ghc7102" }:
  let
    inherit (nixpkgs) pkgs;
  
    # Please note that Sqitch requires PosgreSQL 9.4 which is present in
    # configuration.nix
    sqitch = pkgs.sqitchPg;
  
    # Haskell.
    cabal = pkgs.cabal-install;
    ghc = pkgs.haskell.packages.${compiler}.ghcWithPackages (ps: with ps; [
      http-conduit
  