[racket] Understanding local-expand with definition contexts

Is there any way to have the `test` macro work more like `begin`?

What I am trying to accomplish is something like:

(define-syntax (make-my-unit stx)
   (syntax-parse stx
      [(e ...)
       (with-syntax ([body (local-expand/capture-lifts stx <something>)])
         #'(unit (imports ...) (exports ...) body))]))

Where the defines in #'(e ...) are visible to `unit` so that they can be
used for exports.

--spf
On Mon Jan 05 2015 at 11:32:46 AM Matthew Flatt <mflatt at cs.utah.edu> wrote:

> I think it's more a question of what a definition context is supposed
> to be, rather than how `syntax-local-bind-syntaxes` works.
>
> When you create a new definition context, the context's bindings are
> visible only to expressions that are also in that context. The `test`
> form here creates a new definition context in much the same way as
> `(let () ...)`:
>
>  (let ()
>    (let () (define x 1))
>    x)
>
> In other words, the final `x` really is out of the scope of the
> definition of `x`.
>
> At Mon, 05 Jan 2015 16:26:30 +0000, Spencer Florence wrote:
> > Progress is a new error! I don't think I understand how
> > syntax-local-bind-syntaxes is supposed to work. I extended the previous
> > program:
> >
> > #lang racket
> > (require (for-syntax syntax/parse))
> > (define-syntax (test stx)
> >   (syntax-parse stx
> >     [(_ e)
> >      (define ctx
> >        (if (list? (syntax-local-context))
> >            (cons (gensym) (syntax-local-context))
> >            (list (gensym))))
> >      (define def-ctx (syntax-local-make-definition-context))
> >      (define expd (local-expand #'e ctx (list #'define-values) def-ctx))
> >      (define ids (syntax-parse expd [(def (id) _) (list #'id)]))
> >      (syntax-local-bind-syntaxes ids #f def-ctx)
> >      (internal-definition-context-seal def-ctx)
> >      expd]))
> > (let ()
> >   (test (define x 1))
> >   x)
> >
> > And now I receive the error:  `x: unbound identifier in module in: x`
> > Looking at the docs for `syntax-local-make-definition-context` it seems
> > like I need to provide it with the parent definition-context, but I'm not
> > sure how to get a hold of that.
> >
> > --spf
> >
> > On Mon Jan 05 2015 at 10:00:53 AM Matthew Flatt <mflatt at cs.utah.edu>
> wrote:
> >
> > > The error message is intended for "end users" and turns out to be
> > > misleading for the implementor of an internal-definition context. The
> > > documentation for `define-values` has essentially the same problem: it
> > > describes how `define-values` should work in an internal-definition
> > > context, but it doesn't say how the form interacts with `local-expand`.
> > >
> > > A `define-values` form will only expand in a module or top-level
> > > context. To implement an internal-definition context, you must expand
> > > only far enough to see `define-values` form; in other words, supply
> > > `#'define-values` in the stop list. Then, a partially expanded
> > > `define-values` form must be recognized and handled explicitly, with
> > > tools like `syntax-local-bind-syntaxes` or re-writing to
> > > `letrec-values`, as appropriate for the definition context.
> > >
> > > At Mon, 05 Jan 2015 14:49:03 +0000, Spencer Florence wrote:
> > > > Hey all,
> > > >
> > > > I'm trying to use 'local-expand', however it seems to think its
> never in
> > > a
> > > > definition context. For example:
> > > >
> > > > (require (for-syntax syntax/parse))
> > > > (define-syntax (test stx)
> > > >   (syntax-parse stx
> > > >     [(_ e)
> > > >      (define ctx
> > > >        (if (list? (syntax-local-context))
> > > >            (cons (gensym) (syntax-local-context))
> > > >            (list (gensym))))
> > > >      (local-expand
> > > >       #'e ctx null
> > > >       ;; result is the same with this uncommented
> > > >       #;(syntax-local-make-definition-context))]))
> > > > (let ()
> > > >   (test (define x 1))
> > > >   x)
> > > >
> > > > errors with a "define-values: not in a definition context in:
> > > > (define-values (x) 1)"
> > > >
> > > > Can anyone provide any insight into what is going on?
> > > >
> > > > --spf
> > > > ____________________
> > > >   Racket Users list:
> > > >   http://lists.racket-lang.org/users
> > >
>
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