class Greeter
	def initialize &block
		if block
			@block = block
		else
			@block = proc { |name|
				"Hello #{name}!"
			}
		end
	end
	def greet name = nil
		name = 'world' unless name
		@block.call name
	end
end

greeter = Greeter.new
puts greeter.greet

greeter = Greeter.new do |name|
	"Hi #{name}"
end
puts greeter.greet('John')