From: "Maciek Godek" <pstrychuj@gmail.com>
To: "Kjetil S. Matheussen" <k.s.matheussen@notam02.no>
Cc: guile-user@gnu.org
Subject: Re: References/locations
Date: Mon, 11 Aug 2008 01:00:21 +0200 [thread overview]
Message-ID: <e2ceda030808101600k2469efa7k56800fa8d480d3c@mail.gmail.com> (raw)
In-Reply-To: <Pine.LNX.4.64.0808082021001.5443@ttleush>
Kjetil:
>> Hi,
>> it's me again, asking silly questions.
>
> Not at all, your questions are very good. :-)
That's werid. Every time I write a post I've got the
strange feeling that I'm thinking in the way that
should be forbidden :)
I can give you the background of this idea.
I've been trying to implement a vector-based
object-oriented system (I'm rather reluctant towards
goops). I imagine that it could be used in the
following manner (borrowed from C++):
(define sphere
(class
() ;; public slots
(x y radius) ;; private slots
((move (dx dy) ;; methods
(set! x (+ x dx))
(set! y (+ y dy)))
(scale (factor)
(set! radius (* radius factor))))))
Obviously, the "class" macro should convert methods
to lambdas. For "move" that would be:
(lambda(self dx dy)
(let((x (vector-loc self (get-hash-table properties 'x)))
(y (vector-loc self (get-hash-table properties 'y)))
(radius (vector-ref self (get-hash-table properties 'radius))))
(set! x (+ x dx))
(set! y (+ y dy)))
Obviously, the hash table reference would have to be
evaluated during macro expand to provide the maximum
efficiency.
(If you have any other solutions to this problem, I'm open
to suggestions)
>> 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.
On the other hand the world of scheme seems
to have gotten used to such convention.
> 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>
That's amazing! Whenever I think of something (and imagine
how difficult would it be to implement), you come up with a
solution taking only a few lines of code :)
(I only have to think how would it perform in practice)
Thanks
M.
next prev parent reply other threads:[~2008-08-10 23:00 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 ` References/locations Kjetil S. Matheussen
2008-08-10 23:00 ` Maciek Godek [this message]
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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