Hi,
I am pretty new to jess and I would be very happy if
someone could explain: what I am trying to do is
syntactically wrong or jess is not design to do the
following.
I have used the example of the book
DimmerSwitchDynamic.
I defined a new method getBrightness in the java bean
DimmerSwitchDynamic. What I am try to do is to fire
the rule if the returning value of the method of the
java bean getBrightness is equal to the slot value pv
of template previous-value.
Does jess allow executing functions or methods on the
left hand side of a rule? And if that is the case,
how?
Thank you in advance for your help
Best regards,
Giovanni
**************
CODE*****************************************
(clear)
(watch all)
;Defining the class and link it to the
DimmerSwitchDynamic java bean
(defclass dimmer DimmerSwitchDynamic)
(bind ?ds (new DimmerSwitchDynamic))
(definstance dimmer ?ds )
;Test the methods of the DimmerSwitchDynamic java bean
(call ?ds setBrightness 20)
(bind ?x (call ?ds getBrightness))
(printout t "The getBrightness: " ?x crlf)
;(printout t "The getBrightness---- " (bind ?x (call
?ds getBrightness))crlf)
; Define a template previous-value in order to compare
with Brigthtness value of the java bean
(deftemplate previous-value
(slot pv))
(assert (previous-value (pv 20)))
(facts)
;This rule should only be triggered if the value of
the java bean DimmerSwitchDynamic is equal to the
;value of the slot pv defined in the previous-value
template
(defrule check-brightness
"it triggers if the brightness is = 20"
(previous-value (pv ?n&:( eq (call ?ds getBrightness)
?n)))
=>
(printout t "The new value is equal to the previous
one " crlf))
(run)
********** ERROR MESSAGE
******************************************
Jess, the Rule Engine for the Java Platform
Copyright (C) 2004 Sandia Corporation
Jess Version 7.0a1 9/17/2004
This copy of Jess will expire in 11 day(s).
==> f-0 (MAIN::dimmer (brightness 0) (class
<External-Address:java.lang.Class>) (OBJECT
<External-Address:DimmerSwitchDynamic>))
<=> f-0 (MAIN::dimmer (brightness 20) (class
<External-Address:java.lang.Class>) (OBJECT
<External-Address:DimmerSwitchDynamic>))
The getBrightness: 20
==> f-1 (MAIN::previous-value (pv 20))
f-0 (MAIN::dimmer (brightness 20) (class
<External-Address:java.lang.Class>) (OBJECT
<External-Address:DimmerSwitchDynamic>))
f-1 (MAIN::previous-value (pv 20))
For a total of 2 facts.
Jess reported an error in routine HasLHS.addPattern.
Message: Variable used before definition: ds.
Program text: ( defrule check-brightness "it
triggers if the brightness is = 20" ( previous-value (
pv ?n & : ( eq ( call ?ds getBrightness ) ?n ) ) ) = >
( printout t "The new value is equal to the previous
one " crlf ) ) at line 29.
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