Just a reminder of duck typing: Haskell style => function applied to parameter, e.g f(x) Ruby duck type style => parameter applies function to itself e.g x.f()

Just a reminder of duck typing: Haskell style => function applied to parameter, e.g f(x) Ruby duck type style => parameter applies function to itself e.g x.f() An example: module Dialable def dial # do stuff with self puts "Dialling..." end end # I wouldn't do this, but... class String include Dialable end # So, phone number as a string can be dialled my_phone_number = "01 23 45678" my_phone_number.dial Dialling... # I'd rather do this class PhoneNumber < String include Dialable end my_phone_number = PhoneNumber.new "01 23 45678" my_phone_number.dial Dialling... # now you get an error on non phone number strings "just a random string".dial NoMethodError: undefined method `dial' for "just a random string":String my_phone_number == "01 23 45678" => true my_phone_number == "just a random string" => false You get all the regex and string functions for free too.