[racket] Understanding local-expand with definition contexts

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
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.racket-lang.org/users/archive/attachments/20150105/dca6a1dc/attachment-0001.html>