anchor.diff:  } // stdenv.lib.optionalAttrs (cross != null) {
     name = "${cross.config}-ghc-${version}";
   
  -  # Some fixes for cross-compilation to iOS. See https://phabricator.haskell.org/D2710 (D2711,D2712,D2713)
  -  patches = [ ./D2710.patch ./D2711.patch ./D2712.patch ./D2713.patch ];
  -
     preConfigure = commonPreConfigure + ''
       sed 's|#BuildFlavour  = quick-cross|BuildFlavour  = perf-cross|' mk/build.mk.sample > mk/build.mk
     '';
  
positive.code: 
    commonBuildInputs = [ ghc perl autoconf automake happy alex python3 ];
  
    version = "8.1.20161224";
  
    commonPreConfigure =  ''
      sed -i -e 's|-isysroot /Developer/SDKs/MacOSX10.5.sdk||' configure
  
negative.code: in stdenv.mkDerivation (rec {
    inherit version;
    name = "ghc-${version}";
    rev = "b4f2afe70ddbd0576b4eba3f82ba1ddc52e9b3bd";
  
    src = fetchgit {
      url = "git://git.haskell.org/ghc.git";
      inherit rev;
      sha256 = "1h064nikx5srsd7qvz19f6dxvnpfjp0b3b94xs1f4nar18hzf4j0";
    };
  
    postPatch = "patchShebangs .";
  