From: Markus <markus@...>
Date: 2004-10-08T00:27:57+09:00
Subject: Re: Range behavior (Re: [RCR] New [] Semantics)

On Thu, 2004-10-07 at 07:11, trans. (T. Onoma) wrote:

> --only Numeric ranges can be Continuous.

     Not so.  Time ranges, for example, can be Continuous, as could
Colour or FuzzyTruthValue or... 

> Consider further how succ determines successive members --a Range is an 
> indeterminate ordered set built by iteration. Oddly one defines a Range with 
> a first and last argument, but iterations are supposed to be defined by a 
> seed (first) and the number of successive iterations. 

     Supposed by whom?  You can just as easily define an iteration with
a termination test (e.g. iterating over the lines of a File).

> And there is good 
> reason for this: there is no way to be sure that any given _last_ is a member 
> of the set! Look at this:
> 
>   class ShrinkyDink
>     def initialize(x); @x = x.to_i; end
>     def succ; @x - 1; end
>     def <=>(b); @x <=> b; end
>   end
> 
>   rng = ShrinkyDink.new(0)...ShrinkyDink.new(100)
> 
> Not only is ShrinkyDink.new(100) not a member of the range, but nothing 
> "inbetween" the two is either!

     This fails because the implementation of either succ or <=> is
aberrant; by definition x.succ > x, while that is not the case for
ShrinkyDinks.  If you start going down that path (e.g. "but what if they
write:

    def ShrinkyDink.to_s()
        `rm -f *`
        end

"?) no answer will withstand scrutiny.  

-- Markus