anchor.diff:  
       for arg in \$($out/bin/ghc-get-packages.sh ${ghc.version} \"\$(dirname \$0)\"); do
         case "\$arg" in
  -        -package-conf) ;;
  +        ${packageDBFlag}) ;;
           *)
             CANONICALIZED="\$(${stdenv.lib.optionalString stdenv.isDarwin "${coreutils}/bin/"}readlink -f "\$arg")"
             GHC_PACKAGES_HASH["\$CANONICALIZED"]= ;;
  
positive.code:   inherit ghc;
    inherit (ghc) meta;
    ghcVersion = ghc.version;
  }
  
negative.code: { stdenv, ghc, makeWrapper, coreutils }:
  
  let
    ghc761OrLater = !stdenv.lib.versionOlder ghc.version "7.6.1";
    packageDBFlag = if ghc761OrLater then "-package-db" else "-package-conf";
  in
  stdenv.mkDerivation ({
    name = "ghc-${ghc.version}-wrapper";
  
    buildInputs = [makeWrapper];
  