;;   v ; => 16
;;   (+= v)
;;   v ; => 16
;; 

(define-simple-syntax (s:if-param varname first ...)
  (if (s:get varname)
      (begin
	first
	...)
      '()))

(define-simple-syntax (s:if-sessionvar varname first ...)
  (if (s:session-var-get varname)
      (begin
	first
	...)
      '()))

;; (define-macro (s:if-param varname ...)
;;   (match dat
;; 	 (()    '())
;; 	 ((a)    `(if (s:get ,varname) ,a '()))
;; 	 ((a b)  `(if (s:get ,varname) ,a ,b))))
;;