Re: [Chicken-users] scheduling and coroutines

[Tomtom]

Hi Peter

> Welcome.  I hope you're enjoying Scheme so far :)

Definitely. I've always been amazed by the beauty and expressiveness of
functional programming.
 
> Yeah, you can use multiple value returns. Just change this in the scheduler:
> 
>  (let ((cont (call/cc (queue-remove! q))))
>     ...)
> 
> to this:
> 
>  (let-values (((cont sleep-duration) (call/cc (queue-remove! q))))
>     ...)
> 
> or the slightly shorter:
> 
> (receive (cont sleep-duration) (call/cc (queue-remove! q))
>    ...)
> 
> Then when the coroutine yields to the scheduler, it can just call
> cont with more than one argument.

Sounds promising ! But I must miss something. Let's say I change my scheduler
to this, following your advice:

(define scheduler
  (lambda ()
    (let loop ()
      (if (not (queue-empty? q))
          (receive 
           (cont time) (call/cc (queue-remove! q))
           (printf "sleep:~A~%" time)
           (if 
            (not (unspecified? cont))
            (queue-add! q cont)))
          (loop)))))

Now, how should I change the code in the routine ?

If I don't change anything, obviously it won't work:

(define (routine cont)
  (let loop ((n 10))
    (set! cont (call/cc cont))
    (if (> n 0)
        (loop (- n 1)))))

Error: bad argument count - received 1 but expected 2: #<procedure (? cont 
time)>

Buf if I change the routine by adding one argument to call/cc

(define (routine cont)
  (let loop ((n 10))
    (set! cont (call/cc cont n))
    (if (> n 0)
        (loop (- n 1)))))

Error: bad argument count - received 2 but expected 1: #<procedure
(call-with-current-continuation proc1295)>

Well, I guess it's normal too, as call/cc is taking only one argument - so how
am I supposed to pass this second argument ?

cheers,

Tom