Re: JESS: question about writing rule that is based on comparing the number of one kind of facts and that of another

Thanks Wolfgang. This is great.

On Jul 7, 2011, at 5:54 AM, "Wolfgang Laun" <[email protected]> wrote:

> On 7 July 2011 08:25, Felix Chan <[email protected]> wrote:
> Hi,
> 
> I am trying to find a way to write a rule that is based on comparing
> the number of one kind of facts and the number of another kind. I am
> sure experienced JESS users
> 
> Actually, Ernest has seen it a long time ago, and therefore we have...
>  
> must have seen this requirement before and
> likely have a "standard", perhaps elegant way of dealing with it. But
> I am sorry to say that I am still struggling with it after some time.
> 
> ... the CE accumulate!
> 
> (defrule getNumOfCars
>    ?p <- (policy (policyId ?pid))
>    (car (policyId ?pid))
>    ?c <- (accumulate (bind ?count 0)
>                      (bind ?count (+ ?count 1))
>                      ?count
>                      (car (policyId ?pid)))
>    =>
>    (modify ?p (numOfCars ?c))
> )
> (defrule getNumOfDrivers
>    ?p <- (policy (policyId ?pid))
>    ?c <- (accumulate (bind ?count 0)
>                      (bind ?count (+ ?count 1))
>                      ?count
>                      (driver (policyId ?pid)))
>    =>
>    (modify ?p (numOfDrivers ?c))
> )
> 
> You can remove the queries.
> -W