Ruby1.9のブロックについて勉強した ref: http://qiita.com/items/413f710b126a869cb797

file0.rb

(1..3).map {|x| x * 2} # => [2, 4, 6]

file1.rb

a = (1..3).to_enum
a.next() # => 1

file2.rb

def f1(x)
  x * 2
end
(1..3).map {|x| f1(x)} # => [2, 4, 6]

file3.rb

f1 = lambda {|x| x * 2}  # f1とf2は同じ意味。f1とf3はスコープの考えがちょっと違う（割愛）
f2 = ->(x) {x * 2}
f3 = Proc.new {|x| x * 2}
(1..3).map &f1 # => [2, 4, 6]
(1..3).map &f2 # => [2, 4, 6]
(1..3).map &f3 # => [2, 4, 6]

file4.rb

def itr_func
  (1..3).each {|x| yield x}
end
l = []
itr_func {|x| l << x}
l # => [1, 2, 3]

file5.rb

enum = Enumerator.new do |yielder|
  yielder.yield 1
  yielder.yield 2
  yielder.yield 3
end
enum.next() # => 1
enum.next() # => 2
enum.next() # => 3

file6.rb

def itr_func
  (1..3).each {|x| yield x}
end
enum = Enumerator.new do |yielder|
  Object.itr_func {|x| yielder.yield x}
end
enum.next() # => 1
enum.next() # => 2

file7.rb

enum = ->(x){x * 2}
(1..3).map(&enum).map(&enum) # => [4, 8, 12]

file8.rb

class Chainer
  attr_reader :enum
  def initialize(enum)
    @enum = enum
  end
  def chain(&block)
    next_enum = Enumerator.new do |yielder|
      loop do
        yielder.yield block.call(enum.next)
      end
    end
    Chainer.new(next_enum)
  end
end

enum = Enumerator.new do |yielder|
  yielder.yield 1
  yielder.yield 2
  yielder.yield 3
end

proder = ->(x) {x * 2}

Chainer.new(enum).chain(&proder).chain(&proder).enum.to_a  # => [4, 8, 12]