code: def mk_field(field):
    
    assert len(field) == 1
    identifier, contents = next(iter(field.items()))
    contents = dict(list({'units': '', 'n_with_values': 0}.items()) + list(contents.items()))
    return sbp.resolve_type(sbp.Field(identifier=identifier,
                                      type_id=contents.pop('type'),
                                      options=contents))
docs: Instantiates a field specification from a parsed "AST" of a
    field.
  
    Parameters
    ----------
    field : dict
  
    Returns
    ----------
    A Field or a specialization of a field, like a bitfield.