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))))))
