gistfile1.txt

  distinctTTY = name:
    let
      # Does this systemd service have a TTY?                                                                                                                                                                                                             
      hasTTY = service: (service.serviceConfig.TTYPath or null) != null;

      # Get only the systemd services that have a TTY.                                                                                                                                                                                                    
      ttyServices = self: services: lib.filterAttrs (name: value: name == self || hasTTY value) services;

      # Get the names of some systemd services with a stable ordering.                                                                                                                                                                                    
      serviceNames = services: builtins.sort (a: b: a < b) (builtins.attrNames services);

      # Get a stable ordinal for a named service in a collection of services.                                                                                                                                                                             
      servicePosition = name: services:
        lib.findSingle
          (s: s == name)
          (builtins.error "Could not find service")
          (builtins.error "Found multiple services sharing a name")
          (serviceNames (ttyServices name services));

      num = servicePosition name config.systemd.services;
    in
      "/dev/tty${num}";