lewis.rb

#
# start of solution
#
MyString = Class.new(String)

MyString.define_singleton_method(:alphabet) { 'abc' }

MyString.class_eval {
  exclaim_method = proc { |*args|
    count = args.first || 1

    "#{to_s}#{exclamation_mark count}"
  }

  define_method :exclaim, exclaim_method
  define_method :!,       exclaim_method

  define_method(:exclamation_mark) { |count|
    '!' * count
  }
  private :exclamation_mark
}
#
# end of solution
#

require 'rspec/autorun'

describe MyString do
  describe '.alphabet' do
    specify { MyString.alphabet.should == 'abc' }
  end

  describe '#exclaim' do
    subject { MyString.new('lewis') }

    specify { subject.exclaim.should == 'lewis!' }
    specify { subject.exclaim(4).should == 'lewis!!!!' }
  end

  describe '#!' do
    subject { MyString.new('lewis') }

    specify { subject.!.should == 'lewis!' }

    it 'should be the same even if #exclaim is redefined' do
      MyString.class_eval { define_method(:exclaim) { '' } }

      subject.!.should == 'lewis!'
    end
  end

  describe '#exclamation_mark' do
    specify { subject.should_not respond_to(:exclamation_mark) }
  end
end

my_class_keywords.rb

# Please rewrite the MyString definition, without using ruby keywords 
# http://www.ruby-doc.org/docs/keywords/1.9/

class MyString < String
  class << self
    def alphabet
      'abc'
    end
  end

  def exclaim(count = 1)
    "#{self}#{exclamation_mark count}"
  end
  alias :! :exclaim

  private
  def exclamation_mark(count)
    '!' * count
  end
end

j = MyString.new('james')

j.exclaim         # "james!"
j.exclaim(4)      # "james!!!!"
j.!               # "james!"

MyString.alphabet # "abc"