I think Alexander Lamb wrote: [Charset iso-8859-1 unsupported, filtering to ASCII...] > > You really only mean this rule to apply when selectedScript is nil, so > > you should state that explicitly: > > > > (defrule ASP1 > > (OrmedContext > > (readyToRun TRUE) > > (task "script") > > (selectedScript nil) > > (OBJECT ?c) > > ) > > ... > > > > When the rule fires, selectedScript becomes non-nil, and the rule > > won't be reactivated. > > I had thought about that but didn't you say bean properties can't be nil? >
My recollection is that the JavaBeans spec says this; if it doesn't, in any event, it's an assumption made by many JavaBeans containers. As a result, it's bad practive to write Beans that can return null from their getX methods. Nevertheless, sometimes it's unavoidable. Jess does *not* make this assumption, per se; but if you test the value in a slot, Jess won't test for null first -- you have to do it yourself; i.e., Jess assumes that if you compare the value of a slot to another value, then the slot held a value, not a null. In any event, it's definitely OK to test against nil this way. --------------------------------------------------------- Ernest Friedman-Hill Distributed Systems Research Phone: (925) 294-2154 Sandia National Labs FAX: (925) 294-2234 Org. 8920, MS 9012 [EMAIL PROTECTED] PO Box 969 http://herzberg.ca.sandia.gov Livermore, CA 94550 -------------------------------------------------------------------- To unsubscribe, send the words 'unsubscribe jess-users [EMAIL PROTECTED]' in the BODY of a message to [EMAIL PROTECTED], NOT to the list (use your own address!) List problems? Notify [EMAIL PROTECTED] --------------------------------------------------------------------
