Re: Breaking hygiene with syntax-rules?

[Jean Abou Samra <jean@abou-samra.fr>]

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Le vendredi 11 août 2023 à 18:50 -0400, Walter Lewis via General Guile related discussions a écrit :

> Sorry I typed that code offhand and it had some mistakes; should be:
> 
> ```
> (use-modules (srfi srfi-9) (system foreign))
> 
> (define-syntax define-ffi-wrapper
>    (syntax-rules ()
>      ((_ size
>          name wrap unwrap predicate
>          to-pointer from-pointer)
>       (begin
>         (define-record-type name
>           (wrap bv pointer)
>           predicate
>           (bv unwrap)
>           (pointer pointer-ref pointer-set!))
>         (define (to-pointer x)
>           (or (pointer-ref x)
>               (let ((pointer (bytevector->pointer x)))
>                 (pointer-set! x pointer)
>                 pointer)))
>         (define (from-pointer pointer)
>           (wrap (pointer->bytevector pointer size)
>                 pointer))))))
> ```


You could just turn that into a syntax-case macro, use gensym to generate the names, and insert them using with-syntax or quasisyntax. For example (untested):

```
(use-modules (srfi srfi-9) (system foreign))

(define-syntax define-ffi-wrapper
   (lambda (sintax)
     (syntax-case sintax ()
       ((_ size
           name wrap unwrap predicate
           to-pointer from-pointer)
        (with-syntax ((pointer-ref (datum->syntax sintax (gensym "pointer-ref")))
                      (pointer-set! (datum->syntax sintax (gensym "pointer-set!"))))
          #'(begin
              (define-record-type name
                (wrap bv pointer)
                predicate
                (bv unwrap)
                (pointer pointer-ref pointer-set!))
              (define (to-pointer x)
                (or (pointer-ref x)
                    (let ((pointer (bytevector->pointer x)))
                      (pointer-set! x pointer)
                      pointer)))
              (define (from-pointer pointer)
                (wrap (pointer->bytevector pointer size)
                      pointer))))))))
```

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