anchor.diff:    commonBuildInputs = [ ghc perl autoconf automake happy alex python3 ];
   
     version = "8.1.20170106";
  +  rev = "b4f2afe70ddbd0576b4eba3f82ba1ddc52e9b3bd";
   
     commonPreConfigure =  ''
  +    echo ${version} >VERSION
  +    echo ${rev} >GIT_COMMIT_ID
  +    ./boot
       sed -i -e 's|-isysroot /Developer/SDKs/MacOSX10.5.sdk||' configure
     '' + stdenv.lib.optionalString (!stdenv.isDarwin) ''
       export NIX_LDFLAGS="$NIX_LDFLAGS -rpath $out/lib/ghc-${version}"
  
positive.code:     export NIX_LDFLAGS+=" -no_dtrace_dof"
    '';
  in stdenv.mkDerivation (rec {
    inherit version;
    name = "ghc-${version}";
    rev = "b4f2afe70ddbd0576b4eba3f82ba1ddc52e9b3bd";
  
    src = fetchgit {
      url = "git://git.haskell.org/ghc.git";
  
negative.code: 
    postPatch = "patchShebangs .";
  
    preConfigure = commonPreConfigure;
  
    buildInputs = commonBuildInputs;
  
  