code: def markov(
      fn: Optional[Union[Iterable[int], Callable]] = None,
      history: int = 1,
      keep: bool = False,
      dim: Optional[int] = None,
      name: Optional[str] = None,
  ) -> Union[MarkovMessenger, Callable]:
      """
      Markov dependency declaration.
  
      This can be used in a variety of ways:
  
          - as a context manager
          - as a decorator for recursive functions
          - as an iterator for markov chains
  
      :param int history: The number of previous contexts visible from the
          current context. Defaults to 1. If zero, this is similar to
          :class:`pyro.plate`.
      :param bool keep: If true, frames are replayable. This is important
          when branching: if ``keep=True``, neighboring branches at the same
          level can depend on each other; if ``keep=False``, neighboring branches
          are independent (conditioned on their share"
      :param int dim: An optional dimension to use for this independence index.
          Interface stub, behavior not yet implemented.
      :param str name: An optional unique name to help inference algorithms match
          :func:`pyro.markov` sites between models and guides.
          Interface stub, behavior not yet implemented.
      """
      if fn is None:
          # Used as a decorator with bound args
          return MarkovMessenger(
              history=history, keep=keep, dim=dim, name=name
          )
      if not callable(fn):
          # Used as a generator
          return MarkovMessenger(
              history=history, keep=keep, dim=dim, name=name
          ).generator(iterable=fn)
      # Used as a decorator with bound args
      return MarkovMessenger(
          history=history, keep=keep, dim=dim, name=name
      )(fn)
  
imports: import collections
  import functools
  from typing import Callable, Iterable, Optional, TypeVar, Union, overload
  from typing_extensions import ParamSpec
  from pyro.poutine import util
  from .block_messenger import BlockMessenger
  from .broadcast_messenger import BroadcastMessenger
  from .collapse_messenger import CollapseMessenger
  from .condition_messenger import ConditionMessenger
  from .do_messenger import DoMessenger
  from .enum_messenger import EnumMessenger
  from .escape_messenger import EscapeMessenger
  from .infer_config_messenger import InferConfigMessenger
  from .lift_messenger import LiftMessenger
  from .markov_messenger import MarkovMessenger
  from .mask_messenger import MaskMessenger
  from .reparam_messenger import ReparamMessenger
  from .replay_messenger import ReplayMessenger
  from .runtime import NonlocalExit
  from .scale_messenger import ScaleMessenger
  from .seed_messenger import SeedMessenger
  from .substitute_messenger import SubstituteMessenger
  from .trace_messenger import TraceMessenger
  from .uncondition_messenger import UnconditionMessenger
label_desc: Use image node_id 23 for calling a global function with example usage: markov(fn, history, keep, dim, name) and returns: MarkovMessenger, MarkovMessenger, MarkovMessenger