Defining "anonymous" rules in CLIPS

Question

I know that rules in CLIPS are usually given names using defrule. This rule is called rule1:

(deftemplate animal (slot species))

(deffacts animal
  (animal (species dog)))

(defrule rule1
   (animal (species ?name))
   =>
   (printout t ?name crlf))
(reset)

(run)

(exit)
;

But I still don't know whether it is necessary for the rules to be named. Is it possible to define a rule without giving it a name, like this?

(deftemplate animal (slot species))

(deffacts animal
  (animal (species dog)))

(defrule
   (animal (species ?name))
   =>
   (printout t ?name crlf))
(reset)

(run)

(exit)
;

Answer 1

From section 5 of the Basic Programming Guide:

(defrule <rule-name> [<comment>] 
   [<declaration>]
   <conditional-element>*
   =>
   <action>*)

The rule name is required.

To dynamically generate a rule name, use the gensym* function which creates a unique symbol:

CLIPS> 
(deffunction create-anonymous (?conditions ?actions)
   (bind ?str (str-cat "(defrule " (gensym*) " "
                        ?conditions " => " ?actions ")"))
   (build ?str))
CLIPS> (deftemplate animal (slot species))
CLIPS> 
(create-anonymous "(animal (species ?name))"
                  "(printout t ?name crlf)")
TRUE
CLIPS> (rules)
gen1
For a total of 1 defrule.
CLIPS> (ppdefrule gen1)
(defrule MAIN::gen1
   (animal (species ?name))
   =>
   (printout t ?name crlf))
CLIPS>