def boolParam(parameters, name):
    """ boolean parameter value.
    :param parameters: the parameters tree.
    :param name: the name of the parameter.  """
    value = _simple_string_value(parameters, 'BoolParam', name)
    if value not in {'true', 'false'}:
        raise ValueError('BoolParam Value has to be either "true" or "false", was {}.'.format(value))
    return value == 'true'