values

values

[Philippe de Rochambeau]

Hello,
how do you retrieve the first item returned by the values procedure?
I’ve tried (first (values 1 3)), but to no avail, because values doesn’t return a list.
Many thanks.
Philippe

Re: values

[Arvydas Silanskas]

Hi

generally you would use constructs like define-values or let-values to
declare multiple variables which will be bound to the received multiple
values. There is also a more primitive call-with-values construct for
piping those values as arguments to some procedure. To get a list, you
could use `(call-with-values (lambda () (values 1 3)) list)`.

Arvydas

2021-09-26, sk, 14:57 Philippe de Rochambeau via Kawa <kawa@sourceware.org>
rašė:

> Hello,
> how do you retrieve the first item returned by the values procedure?
> I’ve tried (first (values 1 3)), but to no avail, because values doesn’t
> return a list.
> Many thanks.
> Philippe

Re: values

[Philippe de Rochambeau]

Hi Arvydas,
thanks you for your feedback.
I’ve managed to retrieve the 19 from div-and-mod using let-values.
Now, how do I add a procedure called « (halve n) » which when passed a value such as 39, returns 19?
Many thanks.
Philippe

(display (let-values (((a b) (div-and-mod 39 2)))
a))



> Le 26 sept. 2021 à 14:33, Arvydas Silanskas <nma.arvydas.silanskas@gmail.com> a écrit :
> 
> Hi
> 
> generally you would use constructs like define-values or let-values to declare multiple variables which will be bound to the received multiple values. There is also a more primitive call-with-values construct for piping those values as arguments to some procedure. To get a list, you could use `(call-with-values (lambda () (values 1 3)) list)`.
> 
> Arvydas
> 
> 2021-09-26, sk, 14:57 Philippe de Rochambeau via Kawa <kawa@sourceware.org <mailto:kawa@sourceware.org>> rašė:
> Hello,
> how do you retrieve the first item returned by the values procedure?
> I’ve tried (first (values 1 3)), but to no avail, because values doesn’t return a list.
> Many thanks.
> Philippe

Re: values

[Philippe de Rochambeau]

I found a solution:

(define (halve n)
	(let-values (((a b) (div-and-mod n 2)))
	a))


> Le 26 sept. 2021 à 15:25, Philippe de Rochambeau <phiroc@free.fr> a écrit :
> 
> Hi Arvydas,
> thanks you for your feedback.
> I’ve managed to retrieve the 19 from div-and-mod using let-values.
> Now, how do I add a procedure called « (halve n) » which when passed a value such as 39, returns 19?
> Many thanks.
> Philippe
> 
> (display (let-values (((a b) (div-and-mod 39 2)))
> a))
> 
> 
> 
>> Le 26 sept. 2021 à 14:33, Arvydas Silanskas <nma.arvydas.silanskas@gmail.com <mailto:nma.arvydas.silanskas@gmail.com>> a écrit :
>> 
>> Hi
>> 
>> generally you would use constructs like define-values or let-values to declare multiple variables which will be bound to the received multiple values. There is also a more primitive call-with-values construct for piping those values as arguments to some procedure. To get a list, you could use `(call-with-values (lambda () (values 1 3)) list)`.
>> 
>> Arvydas
>> 
>> 2021-09-26, sk, 14:57 Philippe de Rochambeau via Kawa <kawa@sourceware.org <mailto:kawa@sourceware.org>> rašė:
>> Hello,
>> how do you retrieve the first item returned by the values procedure?
>> I’ve tried (first (values 1 3)), but to no avail, because values doesn’t return a list.
>> Many thanks.
>> Philippe
> 

Re: values

[Philippe de Rochambeau]

… and here’s a solution with a local halve procedure:

(let* ((n0 39)
    (halve (lambda (n)
            (div-and-mod n 2))))
            (let-values (((a b) (halve n0)))
                (display a)))

> 
> I found a solution:
> 
> (define (halve n)
> 	(let-values (((a b) (div-and-mod n 2)))
> 	a))
> 
>> 
>> 
>> Hi Arvydas,
>> thanks you for your feedback.
>> I’ve managed to retrieve the 19 from div-and-mod using let-values.
>> Now, how do I add a procedure called « (halve n) » which when passed a value such as 39, returns 19?
>> Many thanks.
>> Philippe
>> 
>> (display (let-values (((a b) (div-and-mod 39 2)))
>> a))
>> 
>> 
>> 
>>> Le 26 sept. 2021 à 14:33, Arvydas Silanskas <nma.arvydas.silanskas@gmail.com <mailto:nma.arvydas.silanskas@gmail.com>> a écrit :
>>> 
>>> Hi
>>> 
>>> generally you would use constructs like define-values or let-values to declare multiple variables which will be bound to the received multiple values. There is also a more primitive call-with-values construct for piping those values as arguments to some procedure. To get a list, you could use `(call-with-values (lambda () (values 1 3)) list)`.
>>> 
>>> Arvydas
>>> 
>>> 
>>> Hello,
>>> how do you retrieve the first item returned by the values procedure?
>>> I’ve tried (first (values 1 3)), but to no avail, because values doesn’t return a list.
>>> Many thanks.
>>> Philippe