Listen

Connect an event to some particular handling code by giving an event handler (method reference) for a particular Event instance.
When the event is raised (or fired) the method (event handler) is invoked with the args given to raise the event.

An event is specified as a name typed to a sig (signature/delegate).
Any method given as an eventhandler/listener must conform to the same sig.

For disconnecting an event from its handling code see Ignore.
For firing an event see Raise.

Grammar

listen <event>, <method-reference>

Examples

use System.Windows.Forms

...
        button = Button(parent=p, autoSize=true, text='One', tag=1)
        listen button.click, ref .clickHandler
...
def clickHandler(source as Object, args as EventArgs)
    pass

Full example showing sig and event declaration and method to raise the event.

# delegate for ActionEvent  <eventName>EventHandler
sig ActionEventHandler(sender as Object, args as EventArgs)

class Generator
	# event declaration for an event called Action
	# event <eventName>Event as <sigName> (<eventName>EventHandler)    
	event actionEvent as ActionEventHandler

	# (protected) method to raise/fire the event for this class 
	# {on,fire}<eventName>Event
	def _onActionEvent(args as EventArgs)      # fireActionEvent
		raise .actionEvent, args

class Listener
	# the event handler method do<eventName>
	def doAction(source as Object, args as EventArgs)
		print 'Event received from [source]'

...
	def driver
		g = Generator()
		l = Listener()
		
		#tie the generator event to the Listener method
		listen g.actionEvent, ref l.doAction

# Todo example using closure/anonymous method

Notes

The event handler method must be a reference to a method not a method invocation.
In practice this means that most listen statements will have their second argument as a method name prefixed with ref.