Defines a rule named rule-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. If doc-string is given, then it should be a string. The value can be retrieved by calling the function documentation
with doc-type rule
.
A full description is given in Rules.
(defrule move-train :forward :context trains
(train ?train position ?train-pos)
(signal ?signal position ?signal-pos color green)
(test (= ?signal-pos (1+ ?train-pos)))
-->
((format t "~%Train moving to ~S" ?signal-pos))
(assert (signal ?signal color 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)))
KnowledgeWorks and Prolog User Guide (Unix version) - 24 Mar 2017