[plt-scheme] A macro for declaring class properties, a question

From: Noel Welsh (noelwelsh at gmail.com)
Date: Thu Oct 18 05:46:12 EDT 2007

On 10/18/07, Grant Rettke <grettke at acm.org> wrote:

> (define-syntax property
>   (lambda (stx)

You don't need to unhygenically introduce an identifier, as all
accesses of the field should go through the accessor method, right?

>     (define gen-id ; Source: _TSPL3rdEd_ by Kent Dybvig
>       (lambda (template-id . args)
>         (datum->syntax-object
>          template-id
>          (string->symbol
>           (apply
>            string-append
>            (map
>             (lambda (x)
>               (if (string? x) x
>                   (symbol->string (syntax-object->datum x))))
>             args))))))
>     (syntax-case stx ()
>       [(_ name)
>        (with-syntax
>            ([property-name (gen-id (syntax name) "field-" (syntax name))])
>          (syntax
>           (begin
>             (field (property-name null))

Maybe use case-lambda for the accessor, as you have exactly two cases:
no args or one arg (not sure if case-lambda works in the class system)

>             (define/public (name . args)
>               (if (null? args) property-name
>                   (set! property-name (car args)))))))])))

Something like this would do:

(define-syntax property
  (syntax-rules ()
    [(_ name)
     (begin (field super-secret-field-name)
            (define/public name
                [() super-secret-field-name]
                [(value) (set! super-secret-field-name value)])))]))


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