From: Just Another Victim of the Ambient Morality <ihatespam@...>
Date: 2007-11-28T22:35:04+09:00
Subject: Re: Ruby needs continuations...


"Austin Ziegler" <halostatue@gmail.com> wrote in message 
news:9e7db9110711280500j3d7b1c6byf36c6d769c05bcbd@mail.gmail.com...
> On 11/28/07, Vitor Peres <dodecaphonic@gmail.com> wrote:
>> On Nov 28, 2007 10:30 AM, Just Another Victim of the Ambient Morality <
>> ihatespam@hotmail.com> wrote:
>> >    How would one do this in Ruby?  You can use .each_with_index and 
>> > index
>> > the other list but that assumes that the other list is indexable, which
>> > only happens to be true of arrays but is not true in general.  I've 
>> > thought
>> > about implementing some Ruby equivalent of zip() (or preferably izip()) 
>> > and
>> > discovered that I can't do so without continuations.
>
> Actually, Ruby 1.9 is losing continuations (hard to do with native
> threads, expensive for stack frame manipulation in JRuby). However,
> you don't need continuations to do parallel iteration, as Vitor
> suggests:
>
>> Ruby does, however, have an implementation of zip in Enumerable. You can 
>> do
>>
>> list1 = [1, 2, 3, 4]
>> list2 = ['a', 'b', 'c', 'd']
>>
>> list1.zip(list2).each {|num, letter| puts "#{num} #{letter}" }
>>
>> just fine. You'll actually get the same result you would with your Python
>> example.
>
> You're also able to do:
>
>  a.zip(b, c, d, ...)
>
> to iterate multiple lists in parallel.

    Thank you, both, for pointing this out!
    Considering my failure to create such a method, I was about to ask how 
such a thing was implemented but then I just tried it out and I've 
discovered how: arrays.  I've already mentioned that not all containers are 
indexable: linked lists are not and trees are not efficiently. 
Continuations allow even non-indexable containers to be iterated in 
parallel...