{
	type Delegator

	F init(d:Delegator) d.delegate = null

	F default_impl(d:Delegator) 'default implementation'

	F operation(d:Delegator) default_impl(d)

	F operation(d:Delegator) {
		guard defined thing
		guard thing is Fun
		try {
			d.delegate.thing()
		}
		catch(e:ImplNotFound) {
			# Might be unrelated exception, so check and optionally rethrow
			e.callable !== thing throws e
			default_impl(d)
		}
	}

	F operation(d:Delegator) {
		guard d.delegate is Null
		default_impl(d)
	}


	a = Delegator()
	echo(a.operation())

	# There is no method thing(s:Str)
	a.delegate = "abc"
	echo(a.operation())

	# ... now there is method thing(s:Str)
	F thing(s:Str) 'delegate implementation'
	echo(a.operation())
	
}