class Status

	sig ChangedHandler(sender, message as String)

	shared
	
		def set(sender, message as String)
			raise .changed, sender, message

		event changed as ChangedHandler

class Program

	var _statuses = List<of String>()

	def main
		listen Status.changed, ref .statusChanged
		Status.set(this, 'one')
		Status.set(this, 'two')
		assert _statuses == ['one', 'two']

	def statusChanged(sender, message as String)
		_statuses.add(message)