[comp.lang.scheme] Unknown symbol in Elk

vladimir@prosper.EBB.Eng.Sun.COM (Vladimir G. Ivanovic) (12/02/90)

What does the symbol '#v' mean in the following program from a test in the Elk
1.2 distribution?  Both R3RS and the Elk Reference Manual are silent about
'#v'.  MacScheme 2.0 doesn't like it, but Elk happily consumes it.

-- Vladimir

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; -*-Scheme-*-

(define acc)
(define bcc)
(define n 5)

(define (a)
  (if (not (= 0 (call-with-current-continuation
		 (lambda (cc)
		   (set! acc cc) 0))))
      (if (> n 0)
	  (begin
	    (set! n (- n 1))
	    (display "resume b") (newline)
	    (bcc 1))
	  #v)					      ;;; What does this mean?
      acc))

(define (b)
  (if (not (= 0 (call-with-current-continuation
		 (lambda (cc)
		   (set! bcc cc) 0))))
      (begin
        (display "resume a") (newline)
        (acc 1)))
  bcc)

(a)
(b)
(acc 1)

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
--
==============================================================================
   Vladimir G. Ivanovic				Sun Microsystems, Inc
     (415) 336-2315				2550 Garcia Ave., MTV12-33
    vladimir@Sun.COM				Mountain View, CA 94043-1100

      Disclaimer: I speak only for myself.  Your mileage will vary.
==============================================================================

net@opal.cs.tu-berlin.de (Oliver Laumann) (12/02/90)

In article <VLADIMIR.90Dec1213048@prosper.EBB.Eng.Sun.COM> vladimir@prosper.EBB.Eng.Sun.COM (Vladimir G. Ivanovic) writes:
> What does the symbol '#v' mean in the following program from a test in the Elk
> 1.2 distribution?  Both R3RS and the Elk Reference Manual are silent about
> '#v'.  MacScheme 2.0 doesn't like it, but Elk happily consumes it.

It's the non-printing object.  By the way, a more portable way to obtain
a non-printing object (at least when printed with "display") is
(string->symbol "").

--
Oliver Laumann     net@TUB.BITNET     net@tub.cs.tu-berlin.de     net@tub.UUCP