anchor.diff:              ;;
             --branch=*)
               branch="''${flag#*=}"
  +            ;;
  +          --use-stable-version)
  +            use_stable_version=1
  +            ;;
  +          --tag-prefix=*)
  +            tag_prefix="''${flag#*=}"
               ;;
             *)
               echo "$0: unknown option ‘''${flag}’"
  
positive.code: 
      url=""
      branch=""
  
      while (( $# > 0 )); do
          flag="$1"
  
negative.code:   "--url=${builtins.toString url}"
  ] ++ lib.optionals (branch != null) [
    "--branch=${branch}"
  ] ++ lib.optionals stableVersion [
    "--use-stable-version"
    "--tag-prefix=${tagPrefix}"
  ]
  