anchor.diff:  # This module generates the nixos-checkout script, which replaces the
  -# NixOS and Nixpkgs source trees in /etc/nixos/{nixos,nixpkgs} with
  -# Git checkouts.
  +# Nixpkgs source trees in /etc/nixos/nixpkgs with a Git checkout.
   
  -{config, pkgs, ...}:
  +{ config, pkgs, ... }:
   
   with pkgs.lib;
   
  
positive.code:             nix-env -iA nixos.pkgs.git || nix-env -i git
          fi
  
          # Move any old nixos or nixpkgs directories out of the way.
          backupTimestamp=$(date "+%Y%m%d%H%M%S")
  
          if [ -e nixos -a ! -e nixos/.git ]; then
              mv nixos nixos-$backupTimestamp
          fi
  
          if [ -e nixpkgs -a ! -e nixpkgs/.git ]; then
              mv nixpkgs nixpkgs-$backupTimestamp
          fi
  
          # Check out the NixOS and Nixpkgs sources.
          git clone git://github.com/NixOS/nixos.git nixos
          git clone git://github.com/NixOS/nixpkgs.git nixpkgs
        '';
     };
  
negative.code:         if [ "$1" == "-h" ] || [ "$1" == "--help" ]; then
            echo "Usage: `basename $0` [PREFIX]. See NixOS Manual for more info."
            exit 0
          fi
  
          prefix="$1"
          if [ -z "$prefix" ]; then prefix=/etc/nixos; fi
  