[racket] Behavior of continuation-mark-set->list and continuation-mark-set-first with respect to key values

Y. that's the solution. Thanks very much

I'm going to read a few more hours of ch. 16, as its obviously a 
weakness on my part.

Also, jeez, what a great paper Flatt et al. is. I know I've said it to 
you before. Won't be the last time, either.


On Sun, May 6, 2012 at 9:57 PM, Robby Findler wrote:

> Do you mean to just leave the quote off of the usage example?
>
> If not, you could do something like the below (note that this doesn't
> do a good job of error reporting and the test module requires a git
> version of racket to run).
>
> Robby
>
> #lang racket
>
> (define-syntax-rule
>   (with-continuation-marks keys vals body)
>   (with-continuation-marks/proc keys vals (λ () body)))
>
> (define (with-continuation-marks/proc keys vals thunk)
>   (let loop ([keys keys]
>              [vals vals])
>   (cond
>     [(null? keys)
>      (thunk)]
>     [else
>      (with-continuation-mark (car keys) (car vals)
>        (loop (cdr keys)
>              (cdr vals)))])))
>
> (module+ test
>   (require rackunit)
>   (check-equal?
>    (continuation-mark-set->list
>     (with-continuation-marks '(id1 id2 id3)
>                              '(1 2 3)
>                              (current-continuation-marks))
>     'id1)
>    '(1)))
>
>
> On Sun, May 6, 2012 at 8:10 PM, Galler <lzgaller at optonline.net> wrote:
>> Thanks Robby.
>>
>> I'm attempting to implement the behavior described in Section 3.2 of 
>> your
>> 2007 paper, specifically
>>
>> "each continuation frame can have any number of marks with distinct 
>> keys"
>>
>> by defining a new 'with-continuation-marks' syntax which will set up
>> arbitrary number of nested 'with-continuation-mark' calls in response 
>> to a
>> list of keys
>>
>> As Eli B. picked up on earlier, I'm having trouble with Chapter 16 of 
>> the
>> Racket Guide and its a mess at the moment.
>>
>>
>>
>> Is there a basic example of pattern matching for a list of arbitrary 
>> number
>> of elements (including zero)? I
>>
>>
>> ; usage (with-continuation-marks '(id1 id2 id3) body)
>>
>> ;this doesn't work because of bad pattern matching in the
>> with-continuation-marks macro.  (make-binding ...) just sets up 
>> storage.
>> ;its the '(id1 id2 id3) in the arguments that's causing the problem.
>>
>>
>> (define-syntax with-continuation-marks
>>  (syntax-rules ()
>>    [(with-continuation-marks (id) body) (with-continuation-mark id
>> (make-binding id) body)]
>>    [(with-continuation-marks (id1 id2 ...) body) 
>> (with-continuation-mark id1
>> (make-binding id1) (with-continuation-marks (id2 ...) body ))]))
>>
>>
>>
>> On Sun, May 6, 2012 at 9:56 AM, Robby Findler wrote:
>>
>>> continuation-mark-set->list always does return all of the bindings,
>>> but continuation marks are carefully designed to avoid breaking tail
>>> recursion (they let you understand the tail behavior of your 
>>> program,
>>> more accurately) so that's why you see only one binding.
>>>
>>> continuation-mark-set-first can be more efficient than
>>> continuation-mark-set->list and it is more likely to work in 
>>> futures.
>>> That's the only reason it exists.
>>>
>>> Robby
>>>
>>> On Sat, May 5, 2012 at 11:02 PM, Galler <lzgaller at optonline.net> 
>>> wrote:
>>>>
>>>> BACKGROUND:
>>>>
>>>> Per the documentation:
>>>>
>>>> with-continuation-mark  causes a key to be associated with a 
>>>> binding
>>>> within
>>>> a continuation frame
>>>>
>>>> continuation-mark-set->list returns the binding(s) associated with 
>>>> that
>>>> particular key, for any given continuation-mark-set
>>>>
>>>> while
>>>>
>>>> continuation-mark-set-first returns the first (innermost) binding
>>>> associated
>>>> with a particular key
>>>>
>>>> QUESTIONABLE  BEHAVIOR
>>>>
>>>> The issue is:
>>>>
>>>> if a key is reused, the only binding continuation-mark-set->list 
>>>> returns
>>>> is
>>>> the innermost binding.
>>>>
>>>> So continuation-mark-set->list could only possibly return **one** 
>>>> value
>>>>
>>>> and
>>>>
>>>> continuation-mark-set-first  appears redundant
>>>>
>>>> Is that the desired behavior? I would have expected
>>>> continuation-mark-set->list to return all the bindings for a 
>>>> particular
>>>> key.
>>>>
>>>> Additionally, I suspect continuation-mark-set->context has to be
>>>> implemented
>>>> using the 'return a list of all bindings for a single key' 
>>>> behavior,
>>>> since
>>>> the documentation indicates it uses a single private key.
>>>>
>>>>
>>>> EXAMPLE
>>>>
>>>> #lang racket
>>>> (with-continuation-mark 'global  'outermost-value
>>>>  (let/cc k-outer
>>>>    (with-continuation-mark 'global 'middle-value
>>>>      (let/cc k-inner
>>>>        (with-continuation-mark 'global 'inner-value (begin
>>>>                                                       (display
>>>> (continuation-mark-set->list (current-continuation-marks) 'global))
>>>>                                                       (newline)
>>>>                                                       (display
>>>> (continuation-mark-set->list (continuation-marks k-inner) 'global))
>>>>                                                       (newline)
>>>>                                                       (display
>>>> (continuation-mark-set->list (continuation-marks k-outer) 'global))
>>>>         ))))))
>>>>
>>>> ;Returns
>>>>
>>>> ;(inner-value)
>>>>
>>>> ;(middle-value)
>>>>
>>>> ;(outermost-value)
>>>>
>>>> but I would have expected:
>>>>
>>>> ;Returns
>>>>
>>>> ;(inner-value) (middle-value) (outermost-value)
>>>>
>>>> ;(middle-value) (outermost-value)
>>>>
>>>> ;(outermost-value)
>>>>
>>>>
>>>> Thanks very much for looking at this.
>>>>
>>>> R/
>>>>
>>>> Zack
>>>> ____________________
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