anchor.diff:  
       substituteInPlace src/rust-installer/gen-install-script.sh \
         --replace /bin/echo "${coreutils}/bin/echo"
  +    substituteInPlace src/rust-installer/gen-installer.sh \
  +      --replace /bin/echo "${coreutils}/bin/echo"
     '';
   
     buildInputs = [ which file perl curl python27 makeWrapper git valgrind procps ];
  
positive.code: 
    src = fetchgit {
      url = https://github.com/rust-lang/rust;
      rev = "63666317214788329e0b7680929b09823f127d83";
      sha256 = "1saf6ycy5dzp1bxypzqisi4g4p0y1czbgr82xbrw5c81x5c274zk";
    };
  
    # We need rust to build rust. If we don't provide it, configure will try to download it.
  
negative.code: 
  */
  
  with ((import ./common.nix) {inherit stdenv; version = "0.13.0-pre-3497-g6539cb4";});
  
  let snapshot = if stdenv.system == "i686-linux"
        then "b880b98d832c9a049b8ef6a50df50061e363de5a"
        else if stdenv.system == "x86_64-linux"
        then "82a09c162474b69d2d1e4e8399086f3f0f4e31c3"
        else if stdenv.system == "i686-darwin"
        then "569055bb10d96ab25f78ecf2c80ffbccd5e69b8d"
        else if stdenv.system == "x86_64-darwin"
        then "cff1f9ebd63dae6890359b7d353bd9486d8ecdfc"
        else abort "no-snapshot for platform ${stdenv.system}";
      snapshotDate = "2015-01-04";
      snapshotRev = "b2085d9";
      snapshotName = "rust-stage0-${snapshotDate}-${snapshotRev}-${platform}-${snapshot}.tar.bz2";
  
  in stdenv.mkDerivation {
  