From: Robert Klemme <bob.news@...>
Date: 2005-10-01T20:46:45+09:00
Subject: Re: Lazy evaluaton (was Re: In your opinion....)

Devin Mullins <twifkak@comcast.net> wrote:
> gabriele renzi wrote:
>
>> Think for example of the IO monad: it allows you to state that you
>> should, say, print "hello" before "world".
>> The rest of the program is still happy, functional and lazy, since he
>> does'nt really care about the console output.
>
> The word "lazy", and the impression I was forming about monads from
> reading these posts, inspired this simple doodad. Is this useful? Is
> it already implemented in some other Ruby library out there?
>
> class Lazy
>  (instance_methods - %w{__send__ __id__}).each {|meth| undef_method
>  meth } def initialize(blk)
>    @blk = blk
>  end
>  def method_missing(*a,&b)
>    @inst = @blk.call unless defined? @inst
>    @inst.send(*a,&b)
>  end
> end
>
> def lazy(&blk)
>  Lazy.new blk
> end

Delegate comes to mind.  Not really shorter...

require 'delegate'
class Lazy < Delegator
  alias :init :initialize

  def initialize(&b)
    super(nil)
    @bl = b
  end

  def __getobj__
    if @bl
      @obj = @bl.call()
      init(@obj)
      @bl = nil
    end
    @obj
  end
end
def lazy(&b)Lazy.new(&b)end

Only advantage seems that one can reuse lib code for delegation and 
initialization.

Kind regards

    robert