This is a minor complaint. Why can't one use nil to match an empty list? Consider the following:
(deffacts init (sprocket 1 spacely) (sprocket 2)) (defrule non-nil-match (sprocket ?id ?name&~nil $?) => (printout t "sprocket " ?id " is named " ?name "." crlf)) (defrule nil-match-1st-try (sprocket ?id nil $?) => (printout t "sprocket " ?id " is unnamed (1st try)." crlf)) (defrule nil-match-2nd-try (sprocket ?id nil) => (printout t "sprocket " ?id " is unnamed (2nd try)." crlf)) (defrule nil-match-3rd-try (sprocket ?id) => (printout t "sprocket " ?id " is unnamed (3rd try)." crlf)) Running this program results in: Jess> (run) sprocket 2 is unnamed (3rd try). sprocket 1 is named spacely. 3 Jess> Only the pattern (sprocket ?id) matches (sprocket 2) with no following symbols. I would have thought that (sprocket ?id nil) at least would also work, i.e. nil matching the empty list, especially considering that ~~nil matches a non-null symbol. Perhaps my concept of nil is influenced too much by Lisp. Thanks, -Steve Solomon -------------------------------------------------------------------- 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] --------------------------------------------------------------------
