From: ahoward <ahoward@...>
Date: 2002-11-20T04:09:56+09:00
Subject: Re: Thoughts on generators

On 19 Nov 2002, Martin DeMello wrote:

[snip]
M> Has anyone done something like this already?
[snip]

  i have been using this.  the iterator is compliments of Pit Capitain.

  this doesn't work with threads but i learned a lot from it...

eg.


  a = ['fee','fie','foe','fum']
  h = {0 => 'fee', 1 => 'fie', 2 => 'fum', 3 => 'fum'}

  ai = a.iterator
  hi = h.iterator

  while ((n = ai.next)) do
    print n.inspect, ' '
  end; print "\n"

  # >> "fee" "fie" "foe" "fum"

  while ((n = hi.next)) do
    print n.inspect, ' '
  end; print "\n"

  # >> [0, "fee"] [1, "fie"] [2, "fum"] [3, "fum"]

  each a, h do |elem, kv|
    print elem.inspect, ' ', kv.inspect, ' '
  end; print "\n"

  # >> "fee" [0, "fee"] "fie" [1, "fie"] "foe" [2, "fum"] "fum" [3, "fum"]


source.

--------cut--------
module Enumerable
  class Iterator

  public

    attr_reader :enumerable, :has_next

    def initialize enumerable, end_value = nil, &end_block
      @enumerable = enumerable
      @end_value = end_value
      @end_block = end_block
      initialize_fetch_block
    end

    def next
      @has_next ? fetch_next_element : fetch_end_value
    end

    def rewind
      initialize_fetch_block
      self
    end

  protected

    def initialize_fetch_block
      callcc do |@after_fetch|
	@has_next = true
	@enumerable.each do |@next_element|
	  callcc do |@next_fetch| @after_fetch.call end
	end
	@has_next = false
	@next_fetch = nil
	@after_fetch.call
      end
      @after_fetch = nil
    end

    def fetch_next_element
      result = @next_element
      callcc do |@after_fetch| @next_fetch.call end
      @after_fetch = nil
      result
    end

    def fetch_end_value
      @end_block ? @end_block.call : @end_value
    end
  end

  def iterator
    @iterator = Iterator.new self
  end
end

module Kernel
  def each(*enumerables, &block)
    iterators = enumerables.collect{|e| e.iterator}
    while true
      args = iterators.collect{|i| i.next}
      if args.detect{|arg| arg}
	block.call *args
      else
	return enumerables
      end
    end
  end
end
--------cut--------



-ara


-- 

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 | Ara Howard
 | NOAA Forecast Systems Laboratory
 | Information and Technology Services
 | Data Systems Group
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 | Email: ahoward@fsl.noaa.gov
 | Phone:  303-497-7238
 | Fax:    303-497-7259
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