Yes. Sorry. My bad, I had coded by copy&paste my previous example and is
obviously not going to work.
Indeed dynamic-wind works as it should:
mgubi@Ulrike guile3-usr % bin/guile
GNU Guile 3.0.1
Copyright (C) 1995-2020 Free Software Foundation, Inc.
Guile comes with ABSOLUTELY NO WARRANTY; for details type `,show w'.
This program is free software, and you are welcome to redistribute it
under certain conditions; type `,show c' for details.
Enter `,help' for help.
scheme@(guile-user)> (call-with-values (lambda ()
(dynamic-wind (lambda () (display "initialize\n"))
(lambda () (values "a" "b" "c"))
(lambda () (display "finalize\n"))))
(lambda body body))
initialize
finalize
$2 = ("a" "b" "c")
It seems to me a very good solution to my problem. Thanks a lot to all!
Max
> On 18. Mar 2020, at 16:08, to...@tuxteam.de wrote:
>
> On Wed, Mar 18, 2020 at 03:48:03PM +0100, Massimiliano Gubinelli wrote:
>>
>>> On 18. Mar 2020, at 15:40, Massimiliano Gubinelli <m.gubine...@gmail.com>
>>> wrote:
>>>
>>> Good point with dynamic-wind. Does it pass along also multiple values or
>>> has the same problem?
>>>
>>
>> Does not work...
>>
>> mgubi@Ulrike guile3-usr % bin/guile
>> GNU Guile 3.0.1
>> Copyright (C) 1995-2020 Free Software Foundation, Inc.
>>
>> Guile comes with ABSOLUTELY NO WARRANTY; for details type `,show w'.
>> This program is free software, and you are welcome to redistribute it
>> under certain conditions; type `,show c' for details.
>>
>> Enter `,help' for help.
>> scheme@(guile-user)> (call-with-values (lambda ()
>> (dynamic-wind (lambda () (display "initialize\n"))
>> (lambda () (let ((a (values "a" "b" "c"))) a))
> ^^^^^^ HERE
>> (lambda () (display "finalize\n"))))
>> (lambda body body))
>> initialize
>> finalize
>> $1 = ("a")
>> scheme@(guile-user)>
>>
>> Isn't this a bug??? In my view it breaks composability of scheme code.
>
> Above, marked with HERE is the crocodile eating
> your other values.
>
> If you instead do, in that line
>
> (lambda () (values "a" "b" "c"))
>
> then you get ("a" "b" "c").
>
> The let binding construct only binds one value. There's a
> "let-values" for that.
>
> Cheers
> -- tomás
