;; This is an example of a _good_ JESS function (i.e., something that
;; makes more sense written in procedural style than in declarative style).
;;
;; This function prompts the user with ?qstring, and then validates the
;; response to be either y/yes or n/no (case insensitive). It re-prompts if
;; an invalid response is given.

(deffunction ask-question-yn "Ask a yes/no question and return TRUE/FALSE"
                             (?qstring)
  (bind ?success FALSE)
  (while (not ?success) do
    (printout t ?qstring)
    (bind ?reply (read))
    (if (member$ (lowcase ?reply) (create$ "y" "yes"))
      then (bind ?reply TRUE)
           (bind ?success TRUE)
      else (if (member$ (lowcase ?reply) (create$ "n" "no"))
             then (bind ?reply FALSE)
                  (bind ?success TRUE)
             else (printout t "Please answer yes or no." crlf))))
  ?reply)