Inspired by @Yucato, see also: https://gist.github.com/yucato/6073280

yet_another_pretty_old_woman.rb

puts 'Hello! May I help you?'

$stdin.lazy.reduce(Array.new 3) do |history, message|
  history = ([message.strip!] + history).take 3
  break if history.all? {|msg| msg == 'BYE' }

  reply =
    case message
    when 'BYE'
      nil
    when /^[[:upper:][:space:]]+$/
      "Well, it hasn't happened since #{(1930..1950).to_a.sample} !"
    else
      'Huh? Could you speak up, please??'
    end
  puts reply if reply

  history
end

puts 'Thanks. Come back anytime.'

requires Ruby-2.0.x