From: Robert Klemme <bob.news@...>
Date: 2005-03-31T20:04:49+09:00
Subject: Re: Syntax sugar idea for loops


"Jon Raphaelson" <jonraphaelson@gmail.com> schrieb im Newsbeitrag
news:424BBE2E.5000406@gmail.com...
> Luke Graham wrote:
> > On Thu, 31 Mar 2005 16:54:25 +0900, Lasse Koskela
> > <lasse.koskela@gmail.com> wrote:
> >
> >>On Thu, 31 Mar 2005 16:34:44 +0900, Robert Klemme <bob.news@gmx.net>
wrote:
> >>
> >>>Yeah, "odd" and "even" are much too specific IMHO.  Using the index
is the
> >>>most general solution.
> >>
> >>True, odd and even are rather specific but is that such a bad thing,
> >>really? If the odd-even semantics are a common need, why not add
> >>support for it in the language? I mean, why else would Ruby have
> >>Array.each etc. instead of for (i=0; i < x; i++) which is clearly more
> >>powerful in terms of all the things you can do with it?
> >
> >
> > Internal and external iterators are equivalent given the existance
> > of continuations. It may be interesting to explore the possibilities
> > of representing flow control as an object. To start the debate...
> >
> > for () {
> >  case for.special # Cant think of a better name right now :(
> >  when for.first
> >   ..
> >  when for.last
> >   ..
> >   for.restart if error
> >  else
> >    ...
> >    for.next
> >    puts "We get here, unlike the real next keyword"
> >  end
> > }
> >
> > Please note, I am -not- suggesting these for Ruby. I dont even like
the
> > odd/even idea personally. Im brainstorming to see what is possible and
> > would like to see what others can come up with as well.
> >
>
> This seems to me like something of what generators are in python, which
> is just a function that yields instead of returns. I'm not an expert,
> but they are really powerful and useful for defining custom iterators
> and the like.
>
> This generator is basically an open ended list of integers that vary by
> 2 ( I would like to say that I use ruby and not python, and I'm not
> really fluent in python. So if this is wrong, will someone correct me
> please? )
>
> <snip python code>
>
> def every_other(num):
> while 1:
> num += 2
> yield num
>
>
> odds = every_other(3)
>
> odds.next() #=> 5
> odds.next() #=> 7
> odds.next() #=> 9
> odds.next() #=> 11
> odds.next() #=> 13
> odds.next() #=> 15
>
> .. and so on.
>
> I really like the idea of generators, and think that something like them
> explicity might bee useful in ruby. I know it would be not-quite-trivial
> to write a generator class (and there might be one already,) but they
> are a nifty language feature that python has going for it.

It's been done already for arbitrary Enumerations:
http://www.ruby-doc.org/core/classes/Generator.html

It's trivial for odd or even numbers.

    robert