From: Julian Snitow <vangczung@...>
Date: 2003-03-26T05:44:53+09:00
Subject: Re: External iterators all nice and neat (was: Re: Iterate over two lists in parallel)

> Mauricio Fern�ndez wrote:
> 
>> Credits go to Han Holl [67861] for finding this:
>>
>> batsman@tux-chan:/tmp$ expand -t 2 u.rb
>> ######## put this in 'iteration.rb' or something like that ###
>> module Iteration
>>   class ExternalIterator
>>     def initialize(collection, deathThroes=false)
>>       @collection = collection
>>       @cont = nil
>>       @deathThroes = deathThroes
>>     end
>>     def get
>>       @cont.call if @cont
>>       @collection.each { |elem|
>>         callcc { |@cont|
>>           return elem
>>         }
>>       }
>>       @cont = nil  # reset the continuation
>>       return nil unless @deathThroes
>>       throw :iter_done
>>     end
>>   end
>>   def iter(deathThroes=false)
>>     ExternalIterator.new(self, deathThroes)
>>   end
>> end
>>
>> class Array; include Iteration; end
>>
>> arr = ["foo", "bar", "baz", "qux", "florp", "bzaa", "worble"]
>> ex = arr.iter
>>
>> puts ex.get
>> puts "---"
>> puts ex.get
>> puts "***"
>> batsman@tux-chan:/tmp$ ruby u.rb
>> foo
>> ---
>> bar
>> ---
>> baz
>> ---
>> qux
>> ---
>> florp
>> ---
>> bzaa
>> ---
>> worble
>> ---
>> nil
>> ---
>> foo
>> ***
>>

Whoops.  On testing it, you're right.  The first call *does* spit out 
the entire list.

@hat << Condiments::Ketchup
self.eat(@hat)   # mmmm... hatty