anchor.diff:                ${optionalString (cfg.hostBridge != null) ''
                   HOST_BRIDGE=${cfg.hostBridge}
                 ''}
  -              ${optionalString (length cfg.hostPort > 0) ''
  -                HOST_PORT=${concatStringsSep "," cfg.hostPort}
  +              ${optionalString (length cfg.forwardPorts > 0) ''
  +                HOST_PORT=${concatStringsSep "," (map mkPortStr cfg.forwardPorts)}
                 ''}
                 ${optionalString (cfg.hostAddress != null) ''
                   HOST_ADDRESS=${cfg.hostAddress}
  
positive.code:       '';
      };
  
      hostPort = mkOption {
        type = types.listOf types.str;
        default = null;
        example = [ "8080" ];
        description = ''
          List of forwarded ports from the host to the container. 
        '';
      };
  
  
negative.code:     # Generate a configuration file in /etc/containers for each
      # container so that container@.target can get the container
      # configuration.
      environment.etc =
        let mkPortStr = p: p.protocol + ":" + (toString p.hostPort) + ":" + (if p.containerPort == null then toString p.hostPort else toString p.containerPort); 
        in mapAttrs' (name: cfg: nameValuePair "containers/${name}.conf"
        { text =
            ''
              SYSTEM_PATH=${cfg.path}
  