def parameter_error(procedure, parameter_num, expected_type, parameter):
    """Report a type error for a parameter.  Written as a separate 
       procedure to ensure uniform error messages."""
    raise TypeError(procedure + ": expected " + expected_type + 
                    " for parameter " + repr(parameter_num) +
                    " received " + repr(parameter) +
                    " of type " + repr(type(parameter)))