class Exception

def backtrace_string(current_location = nil)
	if current_location.nil?
		location = nil
	else
		location = "in #{current_location} "
	end
	return "*** Exception #{self.class} #{location}" <<
		"(#{self}) (process #{$$}, thread #{Thread.current}):\n" <<
		"\tfrom " << backtrace.join("\n\tfrom ")
end