anchor.diff:  
     nixpkgs.config.packageOverrides = pkgs: {
       erlang = pkgs.erlangR19;
  +    # TODO: mysql = mysql57;
     };
   }
  
positive.code:   environment.shellAliases.ll = "ls -Glh";
    environment.shellAliases.ls = "ls -G";
  
    nix.nixPath = [ # Use local nixpkgs checkout instead of channels.
      "darwin=$HOME/.nix-defexpr/darwin"
      "darwin-config=$HOME/.nixpkgs/darwin-configuration.nix"
  
negative.code:     leiningen
      openjdk8
  
      # Libraries
      # TODO: openssl
  
      # Lisp
      sbcl
  
      # Miscellaneous
      # FIXME: exercism
      # FIXME: kindlegen
  
      # Nix
      nixops
  