From: Brian Candler <b.candler@...>
Date: 2008-11-04T00:01:51+09:00
Subject: Re: Iterator objects and lazy evaluation

And here's a wrapper for this pattern:

class Enumerator
  def filter(&blk)
    self.class.new do |y|
      each do |*input|
        blk.call(y, *input)
      end
    end
  end
end

a = (1..1_000_000_000).to_enum
a.filter { |out,inp| out << inp if inp % 2 == 0 }.
  filter { |out,inp| out << inp+100 }.
  with_index.each { |inp,c| puts inp; break if c > 10 }

$ ruby19 -v
ruby 1.9.1 (2008-10-28 revision 19983) [i686-linux]
$ ruby19 filter.rb
102
104
106
108
110
112
114
116
118
120
122
124
$
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