datetime.rb

[Time, Date].map do |klass|
  klass::DATE_FORMATS[:variable]     = lambda do |t|
    date = 
    case 
    # display today's date as "today"
    when t >= Date.today then "today"
    # display yesterday's date as 'Yesterday'
    when (t >= Date.yesterday and t <= Date.today) then "yesterday"
    # otherwise, display date: eg. Mon 4th June
    else
      t.strftime("%A #{t.day.ordinalize} %B")
    end
    time = t.strftime(" #{t.strftime("%I").to_i}:%M%p").downcase
    date + time
  end
end