accessor with 2/3 parameters

accessor with 2/3 parameters

[Marco Maggi]

Ciao,

  I wanted to create an accessor called ELM with synopsis:

  (set! (elm obj key) value)
  (elm obj key)

which is the same required by the VECTOR-SET! and
VECTOR-REF pair. For this  both  the #:accessor
keyword of class definition and the explicit
definition:

  (define-method (elm (obj <my-class>) key) ...)
  (define-method ((setter elm) (obj <my-class>) ...) ...)

do not work. I had to use:

  (export elm)
  (set! elm (ensure-accessor
             (make-procedure-with-setter
              (lambda (o key)
                ...)
              (lambda (o key value)
                ...))))

So a working example is:

;; ----------------------------------------

(use-modules (oop goops))

(debug-enable 'debug)
(debug-enable 'backtrace)
(debug-enable 'trace)


(define-class <my-vec> ()
  (v #:init-keyword #:value))

(define elm (ensure-accessor
	     (make-procedure-with-setter
	      (lambda (v k)
		(vector-ref (slot-ref v 'v) k))
	      (lambda (v k value)
		(vector-set! (slot-ref v 'v) k value)))))

(define-method (display (o <my-vec>) (port <port>))
  (display (slot-ref o 'v) port))

(define v (make <my-vec> #:value #(1 2 3)))

(set! (elm v 1) -9)
(display v)(newline)
(display (elm v 0))(newline)
(display (elm v 1))(newline)
(display (elm v 2))(newline)

;; ----------------------------------------

  I do not like it because ELM does not know about
<my-vec>, but at  least ELM is a  generic function.
Is there a better way to do it?

  If there is a solution it could be a good idea to
add the implementation example to the GOOPS
documentation.

--
Marco Maggi

"They say jump!, you say how high?"
Rage Against the Machine - "Bullet in the Head"



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Re: accessor with 2/3 parameters

[Neil Jerram]

"Marco Maggi" <marco.maggi-ipsu@poste.it> writes:

> So a working example is:
>
> ;; ----------------------------------------
>
> (use-modules (oop goops))
>
> (debug-enable 'debug)
> (debug-enable 'backtrace)
> (debug-enable 'trace)
>
>
> (define-class <my-vec> ()
>   (v #:init-keyword #:value))
>
> (define elm (ensure-accessor
> 	     (make-procedure-with-setter
> 	      (lambda (v k)
> 		(vector-ref (slot-ref v 'v) k))
> 	      (lambda (v k value)
> 		(vector-set! (slot-ref v 'v) k value)))))
>
> (define-method (display (o <my-vec>) (port <port>))
>   (display (slot-ref o 'v) port))
>
> (define v (make <my-vec> #:value #(1 2 3)))
>
> (set! (elm v 1) -9)
> (display v)(newline)
> (display (elm v 0))(newline)
> (display (elm v 1))(newline)
> (display (elm v 2))(newline)

Do you need the `ensure-accessor' wrapper in order for this example to
work?  I suspect not.

In other words, I think you should get the same result with

 (define elm (make-procedure-with-setter
 	      (lambda (v k)
 		(vector-ref (slot-ref v 'v) k))
 	      (lambda (v k value)
 		(vector-set! (slot-ref v 'v) k value))))

>   I do not like it because ELM does not know about
> <my-vec>, but at  least ELM is a  generic function.

But you don't actually use the generic-ness here, do you?

> Is there a better way to do it?

Not that I know of.  I'll take a look at the code though.

Regards,
     Neil



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Re: accessor with 2/3 parameters

[Neil Jerram]

Neil Jerram <neil@ossau.uklinux.net> writes:

> Not that I know of.  I'll take a look at the code though.

Well, the following seems to work ...

(use-modules (oop goops))
(define-method (second (l <list>)) (cadr l))
(define-method (set-second (l <list>) val) (set-car! (cdr l) val))
(define-method (second (l <vector>)) (vector-ref l 1))
(define-method (set-second (l <vector>) val) (vector-set! l 1 val))
(define sec (make-procedure-with-setter second set-second))
(sec '(1 2 3)) => 2
(sec #(1 2 3)) => 2
(define l (list 'a 'b 'c))
(set! (sec l) 'fff)
l => (a fff c)
(define l (vector 'a 'b 'c))
(set! (sec l) 'fff)
l => #(a fff c)

In other words, it appears that the args of make-procedure-with-setter
can be generics.

Regards,
     Neil



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Re: accessor with 2/3 parameters

[Marco Maggi]

"Neil Jerram" wrote:
>Well, the following seems to work ...
>[...]
>In other words, it appears that the args of
>make-procedure-with-setter
>can be generics.

Yes! The following appears to do what I want:

(use-modules (oop goops))

(define-class <my-vec> ()
  (v #:init-keyword #:value))

(define-method (my-vec-setter (v <my-vec>) k)
  (vector-ref (slot-ref v 'v) k))

(define-method (my-vec-getter (v <my-vec>) k value)
  (vector-set! (slot-ref v 'v) k value))

(define elm (make-procedure-with-setter
              my-vec-setter my-vec-getter))

(define-method (display (o <my-vec>) (port <port>))
  (display (slot-ref o 'v) port))

(define v (make <my-vec> #:value #(1 2 3)))

(set! (elm v 1) -9)
(display v)(newline)
(display (elm v 0))(newline)
(display (elm v 1))(newline)
(display (elm v 2))(newline)

Thank You!

My real code does not act upon Guile vectors but upon
a custom class that wraps a custom SMOB. I require the
generic-ness of ELM to let other Guile extensions take
it in an attempt to write math functions 'compatible'
with Guile-GSL.

--
Marco Maggi

"They say jump!, you say how high?"
Rage Against the Machine - "Bullet in the Head"



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