From: SonOfLilit <sonoflilit@...>
Date: 2007-02-20T02:56:13+09:00
Subject: Re: For loops don't count down

In math classes, I've seen cases where it's very comfortable that
Sigma (n = b to a) = 0 if b > a.
It was just nice to define something as an empty sum this way
(generalization of solutions).

It's also more according to for(i = a; i < 5; i++) behavior, which is
something very useful. Perhaps we should have syntax for both types.
Or just Range#arrange (awul name) where (a..b).arrange would return
a..a if a<b .

Aur

On 2/19/07, Daniel Schierbeck <daniel.schierbeck@gmail.com> wrote:
> On Mon, 2007-02-19 at 22:38 +0900, Yukihiro Matsumoto wrote:
> > Hi,
> >
> > In message "Re: For loops don't count down"
> >     on Mon, 19 Feb 2007 22:27:02 +0900, SonOfLilit <sonoflilit@gmail.com> writes:
> >
> > |Numeric#step counts down:
> > |
> > |5.step(-1) do |i|
> > | #stuff
> > |end
> >
> > 5.downto(1) do |i|
> > end
>
> Is there a necessity for a range such as 5..0 to be empty? It would
> otherwise be easy to make iteration work for such cases. This is a
> simplified solution that doesn't take into account #exclude_end?
>
>   class Range
>     def each
>       obj = first
>       if first <= last
>         while obj <= last
>           yield obj
>           obj = obj.succ
>         end
>       else
>         while first >= last
>           yield obj
>           obj = obj.pre
>         end
>       end
>     end
>   end
>
> This would of course require that the objects in such a "reverse" range
> respond to #pre, or whatever other name would be more suitable.
>
> I'm basically asking if there is a reason why we shouldn't expand the
> functionality of Range#each, other than backwards compatibility (not
> that that isn't a big consideration.)
>
>
> Cheers,
> Daniel Schierbeck
>
>
>