A Ruby program which checks command line arguments if they are palindromes

palindrome.rb

#!/usr/bin/env ruby
# palindrome.rb

module Palindrome
    ALPHABET = ('a'..'z').to_a + ('A'..'Z').to_a

    def palindrome?
        normalized == normalized.reverse           
    end

    def normalized
        self.split('').select { |char| ALPHABET.include? char }.join('').downcase
    end

end

class String
    include Palindrome
end

ARGV.each do |sentence|
    puts %Q{sentence "#{sentence}" is #{ sentence.palindrome? ? '' : 'not' } palindrome}
end