[racket] Help: Passing a class to a macro and not an identifier

On Wed, Sep 15, 2010 at 16:17, Matthias Felleisen <matthias at ccs.neu.edu>wrote:

>
> Now see Robby's answer.
>

I have, several times, but I must be blind.
The code I gave works for class a%, so certainly a% can be "inspected" by
(interface->method-names (class->interface a%))
during the expansion of the macro, and it generates the functions names
according to the method names, so that their existence is detected at
compile
time (thanks to datum->syntax).
I suspect this is why the last line '(get-the-val)' in the module doesn't
raise
a syntax error.

The only remaining problem I have is to abstract class->singleton over a%,
so that the class can be given as an argument to the macro.

Ah, in fact I've just found a (probably ugly) workaround that I hope to
improve
(see below):
To abstract over a%, I just turned class->singleton into a macro-maker
that takes a class (at compile time) and instantiate define-class->singleton
for a given class.

I am a bit puzzled since this does not match your (kind) answers so I must
have either badly explained my problem, or badly understood your answers
(or both).

Anyway, thanks a lot for your help.

Laurent
P.S.: If anyone knows how to improve this, I'm interested.



<singleton.rkt>
#lang racket

(require (for-syntax racket/class))

(define-syntax-rule (define-singleton-sender func obj meth)
  (begin (printf "define-sender: ~s ~s ~s\n" 'func 'obj 'meth)
         (define (func . args)
           (send/apply (obj) meth args))))

(define-syntax-rule (define-class->singleton define-name cl)
  (define-syntax (define-name stx)
    (syntax-case stx ()
      [(_ obj)
       (with-syntax ([(name (... ...))
                      (map (λ(n)(datum->syntax #'obj n))
                           (interface->method-names (class->interface
cl)))])
         #'(begin (define-singleton-sender name obj name)
                  (... ...)))])))

; Tests

(require "a.rkt"
         (for-syntax "a.rkt"))

; Instantiate the macro for a% :
(define-class->singleton a%->singleton a%)

(define current-a (make-parameter (new a% [val 3])))

(a%->singleton current-a)

(get-the-val)

->
define-sender: get-the-val current-a get-the-val
3
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