[R6RS] libraries

[dyb at cs.indiana.edu]

> > Good point---I think I understand your criteria.  Would this be okay,
> > then?
> >
> >   (library S "scheme://r6rs"
> >     (export A P! s)
> >     (define s '())
> >     (define-syntax A
> >       (syntax-rules ()
> >         [(_ p x) (p s x)]))
> >     (define-syntax P!
> >       (syntax-rules ()
> >         [(_ x y) (set! x (cons y s))])))
> >   (library T "scheme://r6rs"
> >     (import S)
> >     (export P0!)
> >     (define (P0!) (A P! 0)))
> >
> > I assume so, since both the set! and reference to 's' are within S.
>
> Yes.

So any identifier that leaks out of a module is fair game as long as
the module itself exports some sort of assignment abstraction.  So,
I presume, this is okay too:

  (library S "scheme://r6rs"
    (export A P! s)
    (define s '())
    (define-syntax A
      (syntax-rules ()
        [(_ p x) (p 's x)]))
    (define-syntax P!
      (syntax-rules ()
        [(_ x y) (set! x (cons y s))])))
  (library T "scheme://r6rs"
    (import S)
    (export P0!)
    (define-syntax dequote-P!
      (syntax-rules (quote)
        [(_ (quote x) e) (P! x e)]))
    (define (P0!) (A dequote-P! 0)))

Again, both the set! and "reference" to s appear in the exporting module.

Kent