anchor.diff:    # The contents of the configuration file found at $NIXPKGS_CONFIG or
     # $HOME/.nixpkgs/config.nix.
     config =
  -    let {
  +    let
         toPath = builtins.toPath;
         getEnv = x: if builtins ? getEnv then builtins.getEnv x else "";
         pathExists = name:
  
positive.code:   netkittftp = import ../tools/networking/netkit/tftp {
      inherit fetchurl stdenv;
    };
  
  
    netpbm = import ../tools/graphics/netpbm {
      inherit stdenv fetchsvn libjpeg libpng zlib flex perl libxml2;
  
negative.code: 
    allStdenvs = import ../stdenv {
      inherit system stdenvType;
      allPackages = args: import ./all-packages.nix ({ inherit config; } // args);
    };
  
    defaultStdenv = allStdenvs.stdenv;
  