gistfile1.rb

# a class to play with
class Zoo 
  def animals
    ['bison', 'cat']
  end 
end

# add zebras method to the class
zebras = lambda do
  puts "look, i have accesss to the instance scope "+ animals.inspect
end

Zoo.class_eval do
  define_method(:zebras, &zebras)
end

#this works
z= Zoo.new
z.zebras

# we need a lions method with a new argument
lions = lambda do |an_argument|
  puts "look #{an_argument}, i do not have access to the instance scope "+animals.inspect
end

# but we want the method to still be able to be called on the instance with no args,
# so we need to modify the method before being passed to define method
Zoo.class_eval do
  define_method(:lions, lambda do
    instance_exec("fine, sir", &lions)
  end)
end

# but this will fail, because the lambda "lions" is no longer being executed in instance scope
z.lions