From: Robert Dober <robert.dober@...>
Date: 2006-03-24T22:45:41+09:00
Subject: Re: iterator class not working

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On 3/24/06, Peter Ertl <pertl@gmx.org> wrote:
>
> Hello Robert,
>
> thanks for your feedback.
>
> Yield'ing and using Array.[] seems obvious but I want class 'Iterator' to
> work for any 'Enumerable', not only 'Array'.
>
> The intention for using 'binding' is that I expect / hope it will keep
> track
> of the enumeration state inside 'Enumeration.each'. However, I don't know
> if
> that's possible in ruby at all.
>
>
>
> > --- Urspr=FCngliche Nachricht ---
> > Von: "Robert Dober" <robert.dober@gmail.com>
> > An: ruby-talk@ruby-lang.org (ruby-talk ML)
> > Betreff: Re: iterator class not working
> > Datum: Fri, 24 Mar 2006 22:17:32 +0900
> >
> > On 3/24/06, Peter Ertl <pertl@gmx.org> wrote:
> > >
> > > Hi,
> > >
> > > in order to understand ruby better (and for fun reasons of course) I
> try
> > > to
> > > write an iterator class. this way I want to understand  'binding' and
> > > 'callcc' better.
> > >
> > > however, it does not work! :-(
> > >
> > > any help will be greatly appreciated!!!
> > >
> > > ---------------------------------------------
> > >
> > > class Iterator
> > >
> > >   def initialize(enum)
> > >     @context =3D binding
> > >   end
> > >
> > >   def next
> > >     enum =3D eval("enum", @context)
> > >     @context, item =3D callcc do |cont|
> > >       enum.each do |item|
> > >         cont.call binding, item
> >
> >
> >                         ^
> >                         |
> > ------------------------+
> > you are missing "state" here, each time you call next, you start to
> > iterate
> > over your "enum" and
> > jump out of the iterator at the first iteration, that is giving you
> "mary"
> > all the time.
> >
> >
> >       end
> > >     end
> > >     item
> > >   end
> > >
> > > end
> > >
> > > names =3D %w{mary gordy john jane elwood}
> > >
> > > it =3D Iterator.new(names)
> > >
> > > 3.times do
> > >   puts it.next
> > > end
> > >
> > > > mary
> > > > mary
> > > > mary
> > >
> > > Best regards
> > > Peter
> > >
> > >
> > Well I see why it does not work, but I fail to see your design behind
> the
> > thing
> > it could be done like this
> > class Iterator
> >     def initialize(*args); @items=3Dargs;@i=3D-1;end
> >
> >     def next
> > @i+=3D1; return @items[@i] unless block_given?; yield @items[@i]; end
> > end
> > but I do not really know what that would be good for.
> >
> > Cheers
> > Robert
> >
> > --
> > Deux choses sont infinies : l'univers et la b=EAtise humaine ; en ce qu=
i
> > concerne l'univers, je n'en ai pas acquis la certitude absolue.
> >
> > - Albert Einstein
> >
>
>
and you want lazy evaluation, converting the Enumeration into an array is
not an option, right?
I think what we need here are coroutines and we do not have them (yet).
I fail to see a solution, hopefully somebody brighter will enlighten us ;)

Cheers
Robert

--
Deux choses sont infinies : l'univers et la b=EAtise humaine ; en ce qui
concerne l'univers, je n'en ai pas acquis la certitude absolue.

- Albert Einstein

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