Fw: [plt-scheme] Confusing continuation behavior (a question about)

----- Original Message ----- 
From: "Anton van Straaten" <anton at appsolutions.com>
To: "Jos Koot" <jos.koot at telefonica.net>
Cc: <plt-scheme at list.cs.brown.edu>
Sent: Friday, July 18, 2008 2:29 AM
Subject: Re: Fw: [plt-scheme] Confusing continuation behavior (a question 
about)


> Sorry, I didn't mean to be so blunt about it - I was too focused on the 
> problem.

I have the one to be sorry. I did not take your remark as blunt. It was 
right.
May be the following does what is wanted (just following the recipe):

#lang scheme
(define cond1 #f)
(define cond2 #f)
(define (foo-process arg1 arg2 name)

 (define (toggle (arg 'ignore))
  (let ((old-state state))
   (let/cc cc (set! state cc)
    (old-state arg))))

 (define (state ignore)
  (define done1 #f)
  (define done2 #f)
  (printf "~a Passed in args ~a and ~a~n" name arg1 arg2)
  (let loop ()
   (unless done1
    (if cond1
     (begin
      (set! done1 #t)
      (printf "~a Condition 1 is met, going to condition 2~n" name))
     (begin
      (toggle (list name "Condition 1 not met"))
      (loop)))))
  (let loop ()
   (if cond2
    (begin
     (set! done2 #t)
     (printf "~a Condition 2 is met, can finish the process~n" name))
    (begin
     (toggle (list name "Condition 2 not met"))
     (loop))))
  (printf "The process has finished with values ~a and ~a~n" arg1 arg2)
  (let ((result (+ arg1 arg2)) (old-state state))
   (set! state (lambda (ignore) (error 'process "~a called after finish" 
name)))
   (old-state result)))

  toggle)

(define a-process (foo-process 13 29 'aaa))
(define b-process (foo-process 665 1 'bbb))
(a-process)
(set! cond1 #t)
(a-process)
(set! cond2 #t)
(a-process)
(b-process)



;Welcome to DrScheme, version 4.0.2.3-svn17jul2008 [3m].
;Language: Module; memory limit: 600 megabytes.
;aaa Passed in args 13 and 29
;(aaa "Condition 1 not met")
;aaa Condition 1 is met, going to condition 2
;(aaa "Condition 2 not met")
;aaa Condition 2 is met, can finish the process
;The process has finished with values 13 and 29
;42
;bbb Passed in args 665 and 1
;bbb Condition 1 is met, going to condition 2
;bbb Condition 2 is met, can finish the process
;The process has finished with values 665 and 1
;666
;>

>
>
> Anton
>
>
> Jos Koot wrote:
>>
>>
>>
>> Oops. So sorry.
>> Jos
>>>
>>> ----- Original Message ----- From: "Anton van Straaten" 
>>> <anton at appsolutions.com>
>>> To: "Grant Rettke" <grettke at acm.org>
>>> Cc: "PLT-list" <plt-scheme at list.cs.brown.edu>
>>> Sent: Friday, July 18, 2008 1:36 AM
>>> Subject: Re: [plt-scheme] Confusing continuation behavior (a question 
>>> about)
>>>
>>>
>>>
>>>> 2. Jos Koot's solution doesn't achieve the desired effect, since it 
>>>> simply re-executes the whole of 'impl' every time.  impl is local with 
>>>> respect to 'process', so the effect of the set! is lost once control 
>>>> transfers out of the procedure.  This can be seen in the output which 
>>>> repeats "Condition 1 is met, going to condition 2" three times.)
>>>>
>>>> Anton
>>>> _________________________________________________
>>>>  For list-related administrative tasks:
>>>>  http://list.cs.brown.edu/mailman/listinfo/plt-scheme
>>>
>>
>> _________________________________________________
>>  For list-related administrative tasks:
>>  http://list.cs.brown.edu/mailman/listinfo/plt-scheme