anchor.diff:  
   let
     stableVersion = "2.1.15";
  -  previewVersion = "2.2.0a3";
  +  previewVersion = "2.2.0a4";
     addVersion = args:
       let version = if args.stable then stableVersion else previewVersion;
           branch = if args.stable then "stable" else "preview";
  
positive.code:   };
    guiPreview = mkGui {
      stable = false;
      sha256Hash = "110mghkhanz92p8vfzyh4199mnihb24smxsc44a8v534ds6hww74";
    };
  
    serverStable = mkServer {
  
negative.code:   };
    serverPreview = mkServer {
      stable = false;
      sha256Hash = "1jlz8a34q3s1sz9r6swh3jnlp96602axnvh1byywry5fb9ga8mfy";
    };
  }
  