From: Bertram Scharpf <lists@...>
Date: 2005-05-07T06:41:11+09:00
Subject: Re: .. and ... aren't operators, maybe they should be?

Hi,

Am Freitag, 06. Mai 2005, 07:22:09 +0900 schrieb Logan Capaldo:
> I was just wondering if maybe the range construction syntax could be
> implemented as a set of operators?
> 
> ...

> This wouldn't implement the parser much  (I don't think any way) and
> it could be useful for things like
> defining inifinite lazy lists, or other ranges with weird natures
> 
> ...
> 
> (1..inf).take(5) do |x|
>          p x

Say `inf = 1/0.0', that works.

> Ok thats a pretty silly example, but lets say succ was more
> complicated than just self + 1
> 
> Eh maybe I'm crazy and this is useless. Just seems to be in line with
> << and + etc. being changeable.

You may redefine a classes `<=>' operator and its `succ'
method before you use its instances as range limits.

The compare operator is needed for initialization of the
range and for the `include?' test. The `succ' method is used for
`to_a' and `each'.

Here is another infinity implementation:

    class InfClass
      def initialize ; @s = +1 ; end
      def negate ; @s = -@s ; self ; end
      def -@ ; dup.negate ; end
      def <=> oth ; @s ; end
      include Comparable
    end

    class String
      alias oldcmp <=>
      def <=> oth
        oldcmp( oth)  ||  -(oth <=> self)
      end
    end

    Inf = InfClass.new
    puts Inf < "x"
    puts "x"..Inf
    puts -Inf.."x"

This is not a very good example as `succ' doesn't make very
much sense for an infinity value.

Bertram


-- 
Bertram Scharpf
Stuttgart, Deutschland/Germany
http://www.bertram-scharpf.de