ERROR

	outputs a list describing the error just caught, if any.  If there was
	not an error caught since the last use of ERROR, the empty list will
	be output.  The error list contains four members: an integer code
	corresponding to the type of error, the text of the error message (as
	a single word including spaces), the name of the procedure in which
	the error occurred, and the instruction line on which the error
	occurred.