new_contents: from .base import TohuBaseGenerator
  from .primitive_generators import Constant
  
  __all__ = ['as_tohu_generator']
  
  
  def as_tohu_generator(g):
      """
      If g is a tohu generator return it unchanged,
      otherwise wrap it in a Constant generator.
      """
  
      if isinstance(g, TohuBaseGenerator):
          return g
      else:
          return Constant(g)
  
subject: Add helper function to ensure an input value is a tohu generator