recursion - Recursive call to a rule -

i have rule fires thousands of other same rule:

(defrule calculate-temperature     ?zone <- (object (is-a zone) (id ?id-zone) (dew-temperature ?dew-temperature) (delta-r ?delta-r))     (process-action (is cooling))             =>     (bind ?supply-temperature (+ ?delta-r ?dew-temperature))     (modify-instance ?zone (supply-temperature ?supply-temperature))             (printout ?*debug-print* "supply-temperature:", ?supply-temperature crlf)) 

what want modify zone's supply-temperature when can calculate it, i.e. when inside zone defined delta-r , dew-temperature. modification of object keeps on firing in recursice neverendless cycle. best practices avoid these annoying loops, please?

thank nicola

by rule doesn't loop:

clips> (clear) clips>  (defclass zone    (is-a user)    (slot id)    (slot dew-temperature)    (slot supply-temperature)    (slot delta-r)) clips>  (definstances start-instances    (z1 of zone (id 1) (dew-temperature 100) (delta-r 10))) clips>     (deftemplate process-action     (slot is)) clips>  (deffacts start-facts    (process-action (is cooling))) clips> (defglobal ?*debug-print* = nil) clips>  (defrule calculate-temperature    ?zone <- (object (is-a zone)                      (id ?id-zone)                     (dew-temperature ?dew-temperature)                     (delta-r ?delta-r))    (process-action (is cooling))            =>    (bind ?supply-temperature (+ ?delta-r ?dew-temperature))    (modify-instance ?zone (supply-temperature ?supply-temperature))            (printout ?*debug-print* "supply-temperature:", ?supply-temperature crlf)) clips> (watch slots) clips> (reset) ::= local slot id in instance z1 <- 1 ::= local slot dew-temperature in instance z1 <- 100 ::= local slot delta-r in instance z1 <- 10 ::= local slot supply-temperature in instance z1 <- nil clips> (run)    ::= local slot supply-temperature in instance z1 <- 110 clips> 

so it's interactions between rules causing loop.

there 3 general techniques prevent rule looping. first, can remove 1 of facts/instances matching conditions of rule. example, process-action fact:

(defrule calculate-temperature    ?zone <- (object (is-a zone)                      (id ?id-zone)                     (dew-temperature ?dew-temperature)                     (delta-r ?delta-r))    ?p <- (process-action (is cooling))            =>    (retract ?p)    (bind ?supply-temperature (+ ?delta-r ?dew-temperature))    (modify-instance ?zone (supply-temperature ?supply-temperature))            (printout ?*debug-print* "supply-temperature:", ?supply-temperature crlf)) 

second, can modify fact/instance slot value prevent pattern matching. example, delta-r:

(defrule calculate-temperature    ?zone <- (object (is-a zone)                      (id ?id-zone)                     (dew-temperature ?dew-temperature)                     (delta-r ?delta-r&~0))    (process-action (is cooling))            =>    (bind ?supply-temperature (+ ?delta-r ?dew-temperature))    (modify-instance ?zone (supply-temperature ?supply-temperature) (delta-r 0))            (printout ?*debug-print* "supply-temperature:", ?supply-temperature crlf)) 

third (and applicable object pattern matching), rules triggered changes slots explicitly matched in conditions of rules. if want changes delta-r trigger rule, not changes dew-temperature, you'd write rule this:

(defrule calculate-temperature    ?zone <- (object (is-a zone)                      (id ?id-zone)                     (delta-r ?delta-r))    (process-action (is cooling))            =>    (bind ?supply-temperature (+ ?delta-r (send ?zone get-dew-temperature)))    (modify-instance ?zone (supply-temperature ?supply-temperature))            (printout ?*debug-print* "supply-temperature:", ?supply-temperature crlf))