anchor.diff:      export NIX_LDFLAGS+=" -no_dtrace_dof"
     '';
   in stdenv.mkDerivation (rec {
  -  inherit version;
  +  inherit version rev;
     name = "ghc-${version}";
  -  rev = "b4f2afe70ddbd0576b4eba3f82ba1ddc52e9b3bd";
   
     src = fetchgit {
       url = "git://git.haskell.org/ghc.git";
  
positive.code: 
    postPatch = "patchShebangs .";
  
    preConfigure = ''
      echo ${version} >VERSION
      echo ${rev} >GIT_COMMIT_ID
      ./boot
    '' + commonPreConfigure ;
  
    buildInputs = commonBuildInputs;
  
  
negative.code:   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}"
  