From: MonkeeSage <MonkeeSage@...>
Date: 2007-12-03T17:54:59+09:00
Subject: Re: Ruby needs continuations...

On Nov 28, 10:53 am, "Just Another Victim of the Ambient Morality"
<ihates...@hotmail.com> wrote:
> "MonkeeSage" <MonkeeS...@gmail.com> wrote in message
>
> news:4f89dee4-b922-49ef-889f-e281e7ad0e8c@j44g2000hsj.googlegroups.com...
>
>
>
> > On Nov 28, 9:19 am, MonkeeSage <MonkeeS...@gmail.com> wrote:
> >> ========
>
> >> require 'generator'
>
> >> module Enumerable
> >>   def izip(*enumerables)
> >>     enumerables = [self] + enumerables
> >>    generators= enumerables.map { | enum |
> >>       Generator.new(enum)
> >>     }
> >>     whilegenerators[0].next?
> >>       result =generators.map { | gen |
> >>         gen.next
> >>       }
> >>       yield result
> >>     end
> >>   end
> >> end
>
> >> [1,2,3].izip([4,5,6]) { | x, y |
> >>   puts x, y
>
> >> }
>
> >> ========
>
> >> NB. generator.rb says thatgeneratorsare slow in 1.8.
>
> >> Regards,
> >> Jordan
>
> > Ps. The SyncEnumerator class from generator does the same thing as
> > izip:
>
> > SyncEnumerator.new([1,2,3], [4,5,6]).each { | x, y |
> >  puts x, y
> > }
>
>     Thank you, MonkeeSage, this is exactly what I'm looking for!
>     It's interesting thatgeneratorsare slow enough to warn users about its
> lack of speed!  Do you know if it would be any faster implemented with
> continuations?  I'm surprised it's so slow considering Ruby employs green
> threads...

Just for posterity, it should be noted that in this particular example
(and several others from itertools), you don't even need generators;
internal iterators work just fine...

def izip(*enums)
  (enums[0].length).times { | i |
    elems = enums.map { | enum |
      enum[i]
    }
    yield elems
  }
end

izip([1,2,3], [4,5,6], [7,8,9]) { | elem |
  p elem
}

Of course, you have to be wary about gotchas regarding the elements
being iterable and so forth; just thought it was worthy of mention
that this is possible with the built-in iteration construct, without
resorting to external iterators.

Regards,
Jordan