Re: No ending loop occured when using call-with-current-continuaion

[Keith Wright]

> From: Ying Luo <address@hidden>
> 
> Hi,
> 
> When I type commands listed below interactively into guile(not using
> "load"), I found there is a loop without ending occured.
> 
> (define call/cc call-with-current-continuation)
> 
> (define retry #f)
> (define factorial
>   (lambda (x)
>     (if (= x 0)
>         (call/cc (lambda (k) (set! retry k) 1))
>         (* x (factorial (- x 1))))))
> 
> (begin (display (factorial 4))
>        (newline)
>        (display (retry 1))
>        (newline))
> 
> 
> Would you please give me some advice? Thanks a lot!

I advise you not to write infinite loops.  Your
program is equivalent to:

>> (let loop () (display 24) (newline) (loop))

My version of Guile correctly prints 24 over and
over until I hit ^C, at which time it returns to a
prompt.

To see the loop, note that after the call to Factorial,
Retry is set equal to a continuation from inside the
call to Factorial that occurs in the Begin just _before_
the call to Retry.  When Retry is called it finishes
the computation of Factorial, displays it, and calls
Retry.

So don't do that then.

-- 
     -- Keith Wright  <address@hidden>

Programmer in Chief, Free Computer Shop <http://www.free-comp-shop.com>
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