lazy_proxy.rb

class LazyProxy
  
  instance_methods.each do |method| 
    undef_method(method) if method !~ /^__/
  end
  
  def initialize &lazy_proxy_block
    @lazy_proxy_block = lazy_proxy_block
  end
  
  def method_missing(method, *args, &block)
    @lazy_proxy_obj ||= @lazy_proxy_block.call # evaluate the real receiver
    @lazy_proxy_obj.send(method, *args, &block) # delegate unknown methods to the real receiver
  end
  
end

module Kernel
  
  def lazily &block
    LazyProxy.new &block
  end
  
end
couch_potato = lazily { lazily { lazily { [1,2,4,8] } } }

p couch_potato.inject(0) { |total, i| total + i }