anchor.diff:      optionalString;
   
     inherit (sources.${channel})
  +    fetchzipVersion
       rev
       sha256
       version;
  
positive.code:   name = "bcache-tools-${version}";
  
    src = fetchFromGitHub {
      version = 2;
      owner = "wkennington";
      repo = "bcache-tools";
      inherit rev sha256;
  
negative.code: let
    sources = {
      "stable" = {
        fetchzipVersion = 2;
        version = "1.0.8";
        rev = "03bc5a32e5c14b75fb757902754480b8bcc3069e";
        sha256 = "339e97128db8a70c8da4cd51584634dda49d569314a0078361d075bf023580e6";
      };
      "dev" = {
        fetchzipVersion = 2;
        version = "2016-10-06";
        rev = "f3a8d548376295279d2d27fda5764adbe377c55b";
        sha256 = "bd54114561b9c703fb53d29e445fff3042cd3625167b8e8f956a6998309c1402";
      };
    };
  
  