Re: [Chicken-users] Printing procedures returned from call/cc

[Thomas Chust]

On Tue, 31 Jul 2012, Jeronimo Pellegrini wrote:
> [...]
> I was wondering why this happens in Chicken (recent checkout from git):
>
> (let ((lst (call/cc (lambda (x)
>                      (print 'something)
>                      (call/cc (lambda (y)
>                                 (list x y)))))))
>  (print lst)
>  (print (eq? (car lst) (cadr lst)))
>  (print (eqv? (car lst) (cadr lst)))
>
> ==>
> (#<procedure (f_10734 . results1838)> #<procedure (f_10734 . results1838)>)
> #f
> #f
>
> The procedures returned are different continuations (and of course
> they are certainly not eq? or eqv?).
> [...]

Hello,

this is really strange!

Since the second lambda expression is in tail position with respect to the
first, the two continuations x and y are actually equivalent, so at first
I was less surprised by their printed representation than by the results
of the equality predicates.

But then I tried to wrap some other function call around the inner
invocation of call-with-current-continuation -- and the two continuation
procedures still had the same printed representation.

I guess one just cannot rely on intuition in this case ;-)

Ciao,
Thomas

--
When C++ is your hammer, every problem looks like your thumb.

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