[rules-users] forall is satisfied when there is nothing?

[Mark Proctor]

forall is implemented as two notes, see the Clips documentation here. In reality it is just a bit of sugar for those two notes. You might be able to achieve what you want, with your own combination of nots.
http://www.csie.ntu.edu.tw/~sylee/courses/clips/bpg/node5.4.7.html

Mark

On 8 Jan 2014, at 11:32, Sonata <plz.write.to at gmail.com> wrote:

> laune wrote
>> On 08/01/2014, Davide Sottara &lt;
> 
>> dsotty@
> 
>> &gt; wrote:
>>> Indeed it is true by convention, see also
>>> http://en.wikipedia.org/wiki/Universal_quantification
>>> 
>>> The only other alternative is to deprecate quantifiers altogether ;)
>>> 
>> 
>> Ah, *by convention*, yes. One should exercise some care with "vacuous
>> truths", however. Uttering statements such as "All the little green
>> men in my room are from Mars" may not brand you as a liar, but you
>> could be called "batty". ;-)
>> 
>> -W
>> 
>>> Davide
>>> 
> 
> Guys, I am not sure whats the arguing point here. But from a programmer's
> and a Drools engine user's perspective, I would find forall(void) to return
> false more convenient.
> 
> Say for example:
>  forall(Cloth(dried)) then collect()
> Programmingwise, I dont want to execute collect() when the Cloth()
> collection is empty and do extra null checkings.
> Performancewise, I also dont want to call collect() when there is actually
> nothing to perform.
> In terms of semantics, I purposely want to check for isDried is true, it is
> easy to realize from the LHS that I only want to collect clothes when all of
> them are dried, rather than I want to collect also empty air.
> 
> On the contrary, if I really want to do the RHS even though the LHS has
> nothing, I would have written:
>  not( exists( Customer() ) ) then takeanap()
> and I will not write
>  forall( Customer(status == "gone") ) then takeanap()
> because the latter needs to do extra property visits and string comparisons
> and it is so indirect to express what I really want.
> 
> I really dont care what the mathematical definition is unless you tell me
> Drools is a math. engine rather than a rule engine to express business
> requirements. That, I should update myself and take a step back to look at
> Drools again. Just my own opinion :P
> 
> 
> 
> 
> --
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