(define (display-to-string val)
  (let ((exp-port (open-output-string)))
    (display exp exp-port)
    (get-output-string exp-port)))

;;expression as string
(define (write-to-string exp)
  (let ((exp-port (open-output-string)))
    (write exp exp-port)
    (get-output-string exp-port)))

(define (on/off-option-processor name)
  (lambda (option arg-name arg ops)
    (cons (cons name #t) ops)))