From: "Kjetil S. Matheussen" <k.s.matheussen@notam02.no>
To: guile-user@gnu.org
Subject: Re: References/locations
Date: Fri, 08 Aug 2008 20:34:27 +0200 (CEST) [thread overview]
Message-ID: <Pine.LNX.4.64.0808082021001.5443@ttleush> (raw)
In-Reply-To: <cmu-lmtpd-5833-1218211546-4@mail-imap1.uio.no>
"Maciek Godek":
> Subject: References/locations
> To: guile-user@gnu.org
> Message-ID:
> <e2ceda030808071850uc1640e6kf4ffc33699143fd2@mail.gmail.com>
> Content-Type: text/plain; charset=ISO-8859-1
>
> Hi,
> it's me again, asking silly questions.
Not at all, your questions are very good. :-)
> This time I would like to know if there's
> a simple way to store a reference to
> a variable in another variable -- say,
> an element of vector or hash table.
>
> I imagine this could look like this:
> (define v #(1 2 3))
> (define v1 (vector-location v 1))
> v1
> : 2
> (set! v1 10)
> v
> : #(1 10 3)
>
> I've tried to do it using a "procedure with
> setter", but the problem is that set! doesn't
> evaluate its first argument (as long as it's a
> symbol), so I'd have to wrap everything
> up in macros to obtain:
> (set! (vector-location v 1) 10)
>
> Besides I think that the names "hash-ref"
> and "vector-ref" are confusing, since they
> don't return references, but values (therefore
> the names like "vector-get" or "hash-get" would
> be more apropreate)
>
Never thought about that, but it sounds
correct. vector-get and hash-get would
probably be mroe apropreate names.
> I also wonder if there's any point for allowing
> locations to any sorts of variables (similar to
> pointers in C or pointers to C++), that is,
> (define x 10)
> (define y (location x))
> (set! y 20)
> x
> : 20
>
Well, here's a relatively clean way, I think:
(define-macro (location name)
(define new-val (gensym))
`(lambda (,new-val)
(set! ,name ,new-val)))
(define old-set! set!)
(define-macro (set! a b)
`(if (procedure? ,a) ;; Needs a better check.
(,a ,b)
(old-set! ,a ,b)))
guile> (define x 10)
guile> (define y (location x))
guile> (set! y 20)
guile> x
20
guile>
next parent reply other threads:[~2008-08-08 18:34 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <cmu-lmtpd-5833-1218211546-4@mail-imap1.uio.no>
2008-08-08 18:34 ` Kjetil S. Matheussen [this message]
2008-08-10 23:00 ` References/locations Maciek Godek
2008-08-15 10:14 ` References/locations Maciek Godek
2008-08-15 13:55 ` References/locations Clinton Ebadi
2008-08-18 8:09 ` References/locations Maciek Godek
2008-08-18 16:15 ` References/locations Clinton Ebadi
2008-08-08 1:50 References/locations Maciek Godek
2008-08-10 7:51 ` References/locations Stephen Compall
2008-08-15 9:35 ` References/locations Maciek Godek
[not found] ` <e2ceda030808141732r524fc0cehb8ae7c6007550ea6@mail.gmail.com>
[not found] ` <m2wsihltfv.fsf@member.fsf.org>
[not found] ` <e2ceda030808200441q52d9858bv63323055e0f6308a@mail.gmail.com>
2008-08-21 5:05 ` References/locations Stephen Compall
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