JESS: Problems Combining Jess Variables

[Jim VanDragt]

Good Evening All,

I'm attempting my first Jess script tonight and need a little help.  I'm trying to create a new variable (see Problem Line below) by combining ?ostring and ?answer. When I (run) this batch file I receive a Jess error (see below).

How do you combine to variables such as ?ostring and ?answer ?

TIA




--------------------------- Script Snippet ----------------------------

(deftemplate work-surface
    (slot shape (default rectangular))
    (slot product-line (default not-defined))
    (slot order-string (default Z))
    (slot shape-code (default R))
    (slot top-material (default not-defined))
    (slot front-edge (default not-defined))
    (slot question-to-ask (default product-line))
)


(defrule rectangular-work-surface-front-edge-laminate "For top material Laminate"
    (vocabulary (product work-surface))
    ?ws <- (work-surface (shape rectangular) (order-string ?ostring) (question-to-ask ?question) (top-material l))
    (test (eq ?question front-edge))
  =>

    (printout t crlf "Select Front Edge Material" crlf)
    (printout t "===================" crlf)
    (printout t "A - Square-Edge Front, Vinyl" crlf)
    (printout t "C - Square-Edge Front, Wood" crlf)
    (printout t "D - Bullnose Front, Laminate" crlf)
    (printout t "E - Bullnose Front, Wood" crlf)
    (printout t "F - Bullnose Front, Vinyl" crlf)
    (printout t "G - Passage Edge Front, Vinyl" crlf)
    (printout t "K - Contoured Edge Front, Vinyl" crlf)
    (printout t "" crlf)


    (bind ?answer (read))

    (modify ?ws (top-material ?answer) (question-to-ask nil))
    (bind ?combinded-ostring (+ ?ostring ?answer))    <<<<<<< ------------------------ Problem Line

)


--------------------------- Error Snippet ------------------------------

Jess reported an error in routine Value.numericValue
.......
  Message: Not a number: "Z" (type = ATOM).
  Program text: ( batch /jess61p4/jimsjess/firstone.clp )
.....




Jim Van Dragt
Herman Miller Inc.
(616) 654-5285