01.rb

class CLI
  def process(input)
    if input == "q"
      puts "Goodbye"
    elsif input == "tweet"
      puts "tweeting"
    elsif input == "dm"
      puts "direct messaging"
    elsif input == "help"
      puts "helping"
    end
  end
end

02.rb

class CLI
  class QuitCommand
    def match?(input)
      input == "q"
    end
    
    def execute
      puts "Goodbye"
    end
  end

  def TweetCommand
    def match?(input)
      input == "tweet"
    end
  
    def execute
      puts "tweeting"
    end
  end

  class DirectMessageCommand
    def match?(input)
      input == "dm"
    end
  
    def execute
      puts "direct messaging"
    end
  end

  class HelpCommand
    def match?(input)
      input == "help"
    end

    def execute
      puts "helping"
    end
  end

  class NoActionCommand
    def match?(input)
      true
    end
  
    def execute
    end
  end

  def commands
    quit = QuitCommand.new
    tweet = TweetCommand.new
    dm = DirectMessageCommand.new
    help = HelpCommand.new
    no_action = NoActionCommand.new
    [quit, tweet, dm, help, no_action]
  end

  def command_for_input(input)
    commands.find {|command| command.match?(input) }
  end

  def process(input)
    command_for_input(input).execute
  end
end

03.hs

process :: String -> IO ()
process "q"     = putStrLn "quitting"
process "tweet" = putStrLn "tweeting"
process "dm"    = putStrLn "direct messaging"
process "help"  = putStrLn "helping"
process _       = return ()