anchor.diff:  
   /* Cargo binary snapshot */
   
  -let snapshotDate = "2015-06-17";
  +let
  +  snapshotDate = "2016-01-31";
   in
   
   with ((import ./common.nix) {
  
positive.code:   version = "snapshot-${snapshotDate}";
  });
  
  let snapshotHash = if stdenv.system == "i686-linux"
        then "g2h9l35123r72hqdwayd9h79kspfb4y9"
        else if stdenv.system == "x86_64-linux"
        then "fnx2rf1j8zvrplcc7xzf89czn0hf3397"
        else if stdenv.system == "i686-darwin"
        then "3viz3fi2jx18qjwrc90nfhm9cik59my6"
        else if stdenv.system == "x86_64-darwin"
        then "h2bf3db4vwz5cjjkn98lxayivdc6dflp"
        else throw "no snapshot for platform ${stdenv.system}";
      snapshotName = "cargo-nightly-${platform}.tar.gz";
  in
  
  stdenv.mkDerivation {
  
negative.code: 
    src = fetchurl {
      url = "https://static-rust-lang-org.s3.amazonaws.com/cargo-dist/${snapshotDate}/${snapshotName}";
      sha1Confirm = snapshotHashes.sha1;
      inherit (snapshotHashes) sha256;
    };
  
    buildInputs = [ makeWrapper ];
  