Macro

Syntax

defrule rule-name direction &rest body

Arguments

rule-name is a symbol. direction is :forward or :backward . The body is described in Chapter 3, Rules.

Description

Defines a rule of the given name (which must be distinct from any other rule name, context name or KnowledgeWorks class name). If direction is :forward a forward chaining rule is defined, if :backward a backward chaining rule is defined. A full description is given in Rules.

Values

rule-name is returned.

Examples

(defrule move-train :forward :context trains

  (train ?train position ?train-pos)

  (signal ?signal position ?signal-pos colour green)

  (test (= ?signal-pos (1+ ?train-pos)))

  -->

  ((format t "~%Train moving to ~S" ?signal-pos))

  (assert (signal ?signal colour red))

  (assert (train ?train position ?signal-pos)))

(defrule link-exists :backward

  ((link-exists ?town1 ?town2)

   <--

   (or (link ?link town1 ?town1 town2 ?town2)

       (link ?link town2 ?town1 town1 ?town2))

   (cut))

  ((link-exists ?town1 ?town2)

   <--

   (route-exists ?town1 ?town2)))