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

[Mark Proctor]

sorry auto correct issue - two not nodes. I incorrectly wrote “two notes”.

Mark
On 8 Jan 2014, at 14:49, Mark Proctor <mproctor at codehaus.org> wrote:

> 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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