anchor.diff:  
   let
     stableVersion = "2.1.18";
  -  previewVersion = "2.2.0a5";
  +  previewVersion = "2.2.0b1";
     addVersion = args:
       let version = if args.stable then stableVersion else previewVersion;
           branch = if args.stable then "stable" else "preview";
  
positive.code:   };
    serverPreview = mkServer {
      stable = false;
      sha256Hash = "1yvdfczi8ah9m7b49l7larfs678hh7c424i1f73kivfds6211bj5";
    };
  }
  
negative.code:   };
    guiPreview = mkGui {
      stable = false;
      sha256Hash = "0kx68r8kgnsb7710a1a5y64blmw2jl1gv37bzbbivi15dzgmykfh";
    };
  
    serverStable = mkServer {
  