[racket] Problem with macro

Thanks Danny,

I've changed the syntax of the macro as follows by faking keyword
arguments prompt: and handler: and it works now as far as I can tell.

I saw some discussion on the dev list about keyword parameters and
syntax but I didn't quite follow it, so I wasn't sure if it was saying
that keyword parameters in macros  wll or won't be implemented.

;let/set-prompt  is  let type syntax for call-with-continuation-prompt
procedure.
;(let/set-prompt ([prompt: prompt] [handler: handler] args) body)
; prompt and handle are optional
; Examples:
; (let/set-prompt () (+ 1 2 3 4))
; (let/set-prompt ([prompt: prompt-1])  (+ 1 2 3 4))
; (let/set-prompt ([prompt: prompt-1] [handler: handler-1]) (+ 1 2 3 4))
; (let/set-prompt ([prompt: prompt-1] [handler: handler-1] [val 4]) (+
1 2 3 val))
(define-syntax let/set-prompt
  (syntax-rules (prompt: handler:)
[(_ ((prompt:  PROMPT) (handler: HANDLER) ARGS ...) BODY ...)
(call-with-continuation-prompt (let (ARGS ...) (λ () BODY ...)) PROMPT
HANDLER)]
[(_ ((handler: HANDLER) (prompt:  PROMPT) ARGS ...) BODY ...)
(call-with-continuation-prompt (let (ARGS ...) (λ () BODY ...)) PROMPT
HANDLER)]
[(_ ((prompt:  PROMPT)                    ARGS ...) BODY ...)
(call-with-continuation-prompt (let (ARGS ...) (λ () BODY ...))
PROMPT)]
[(_ ((handler: HANDLER)                   ARGS ...) BODY ...)
(call-with-continuation-prompt (let (ARGS ...) (λ () BODY ...))
PROMPT)]
[(_ (                                     ARGS ...) BODY ...)
(call-with-continuation-prompt (let (ARGS ...) (λ () BODY ...)))]))

(define-syntax abort-to-prompt
  (syntax-rules ()
     [(_ VAL) (abort-current-continuation
(default-continuation-prompt-tag) (thunk VAL))]
     [(_ PROMPT-TAG VAL) (abort-current-continuation PROMPT-TAG (thunk VAL))]))


(define prompt-1 (make-continuation-prompt-tag))
(define prompt-2 (make-continuation-prompt-tag))
(define prompt-3 (make-continuation-prompt-tag))

(define (play-with-prompts [p (default-continuation-prompt-tag)])
  (+ 1
     (let/set-prompt ([prompt: prompt-1] [val 10] )  (+ val
        (let/set-prompt ([prompt: prompt-2] [val 100]) (+ val
           (let/set-prompt ([prompt: prompt-3] [val 1000]) (+ val
              (abort-to-prompt p 0) 2000)) 200)) 20))))


(play-with-prompts prompt-1)
(play-with-prompts prompt-2)
(play-with-prompts prompt-3)
(play-with-prompts)

On Sun, Sep 2, 2012 at 12:27 AM, Danny Yoo <dyoo at hashcollision.org> wrote:
>> (let/set-prompt prompt-3 ()
>>                 (+ 1000
>>                    (abort-to-prompt p 0)
>>                    2000))
>>
>> ==>
>>
>> (call-with-continuation-prompt
>>  (let () (λ ()
>>            +
>>            1000
>>            (abort-to-prompt p 0)
>>            2000))
>>  prompt-3)
>>
>>
>>
>> And whoops!  That's where we're getting the funky values back: the use
>> of + just got ripped apart by the macro, by accident.  We popped its
>> bubble, and the components just spilled out into the body of the let.
>
>
> Doh.  Typo.  I meant to say: "... and the components just spilled out
> into the body of the λ".  Sorry about the confusion!