Re: Breaking hygiene with syntax-rules?

[Walter Lewis]

Hi Jean,

On 8/11/23 4:00 AM, Jean Abou Samra wrote:
> This is a known limitation in Guile. Please read
> https://www.gnu.org/software/guile/manual/html_node/Hygiene-and-the-Top_002dLevel.html
>
> I expect that you would be able to fix your macro by using
>
> (define binding-you-want-to-report
>   (let ((private-binding ...) ...)
>    expr...))
>
> or
>
> (define-values (binding-to-export-1 binding-to-export-2 ...)
>   (let ((private-binding ...) ...)
>     (values expr1 expr2 ...)))

Unfortunately this won't work for my use case, since I am writing a 
helper to generate record type definitions. The code is something like 
this (slightly simplified for now):

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

(define-syntax define-ffi-wrapper
  ((_ size
      name wrap unwrap predicate
      to-pointer from-pointer)
   (begin
     (define-record-type name
      (wrap bv pointer)
      predicate
      (pointer get-pointer set-pointer!))
     (define (to-pointer x)
       (or (get-pointer x)
           (let ((pointer (bytevector->pointer x)))
             (set-pointer! x pointer)
             pointer)))
     (define (from-pointer pointer)
       (wrap (pointer->bytevector pointer size)
             #f)))))

Basically it is a wrapper similar to define-wrapped-pointer-type, except 
when you cast it to a pointer it memoizes the pointer for later. (It's 
actually inspired by the vec2 implementation in Dave Thompson's 
Chickadee.) I wanted to avoid writing all this boilerplate by hand for 
each wrapper type, but I ran into this shadowing issue with the internal 
definitions such as get-pointer and set-pointer!.