From: Alex McHale <alexmchale@...>
Date: 2004-05-26T23:15:56+09:00
Subject: Re: defining condititions

This really isn't particularly what you're after, but here's a nibble
that will evaluate an array that  is assumed to be flip-flopping
between ands and ors.  The simple case will be DNF or CNF.

def or_rule conditions
    if conditions.is_a? Array
        conditions.each do |element| return true if and_rule(element) end
        false
    else
        true && conditions
    end
end

def and_rule conditions
    if conditions.is_a? Array
        result = true
        conditions.each do |element| result &&= or_rule(element) end
        result
    else
        true && conditions
    end
end

and_rule([true, [false, false]]) ==> (true AND (false OR false)) ==> false
and_rule([true, [true, false]]) ==>  (true AND (true OR false)) ==> true
and_rule([true, [[true, false], false]]) ==> (true AND ((true AND
false) OR false)) ==> false
and_rule([true, [[true, true], false]]) ==> (true AND ((true AND true)
OR false)) ==> true

Anyway, it's a similar topic, so I thought I would post it.  The only
abnormality is that and_rule([]) is true, or_rule([]) is false, and
and_rule([[]]) is false.

Alex


On Wed, 26 May 2004 19:38:44 +0900, Sascha Doerdelmann
<wsdngtmp@onlinehome.de> wrote:
> 
> Florian Weber <csshsh@structbench.com> wrote:
> > my_set.rules = !name("orange") && hasProperty("color") &&
> > (hasProperty("size") || hasProperty("weight"))
> 
> Apply the composite pattern, see
> http://c2.com/cgi/wiki?CompositePattern
> or
> http://unicoi.kennesaw.edu/~jbamford/csis4650/uml/GoF_Patterns/composite.htm
> 
> Forget about the addComponent, removeComponent messages. You need a
> different way to build composite rules. As in the pattern you need an
> abstract class for all components. Call it AbstractRule and build
> subclasses for composed rules and concrete rules. Implement messages
> like "and", "or", etc. in AbstractRule, each of them should return a
> composed rule. Depending on your implementation of the composed rules
> you might overwrite these messages in composed rules.
> 
> Cheers
> Sascha
> 
>