[racket-dev] Trouble with state, submodules, and module-begin

From: Matthew Flatt (mflatt at cs.utah.edu)
Date: Mon Jun 25 17:38:12 EDT 2012

I think I misunderstood your complaint. If you change the example to

  (module+ sub
    (#%module-begin (m)))

then there's no error. So, I think you're running into the old
only-form-in-module-just-might-expand-to-#%module-begin problem.

The usual solution is form `m' to check whether it's being expanded in
a 'module-begin context, in which case it should wrap itself in
`begin', or something like that.

At Mon, 25 Jun 2012 17:28:23 -0400, Sam Tobin-Hochstadt wrote:
> On Mon, Jun 25, 2012 at 5:14 PM, Matthew Flatt <mflatt at cs.utah.edu> wrote:
> > The expansion of submodules is intended to have a fresh store, just
> > like the expansion of any module. The `#f' initial import is intended
> > to be something like using `(submod "..")' as the initial language,
> > except importing all internal bindings of the module instead of its
> > exports.
> >
> > Can Typed Racket not handle enclosing bindings in the same way that it
> > handles `require's in general?
> Currently, it can.  However, I wanted to make a fairly small change to
> only update the type environment when needed, and it broke because of
> this.  In the context of my example, the `(m)` invocation is expanded
> *before* the inner `#%module-begin` expansion happens, meaning that it
> hits the error case, even though it's expanded inside a module with
> the appropriate `#%module-begin` binding.
> With submodules as they currently work, the inner `#%module-begin` is
> expanded quite late, which I think breaks other possible expectations
> about #%module-begin as well.  Moving it earlier will, I think,
> alleviate all of these issues.
> >
> > At Mon, 25 Jun 2012 17:05:21 -0400, Sam Tobin-Hochstadt wrote:
> >> It appears that the expansion of (module* m #f ...) occurs in a fresh
> >> store, but before running the inner module's `#%module-begin` binding.
> >> To see this, run the program at https://gist.github.com/2991214 , and
> >> note that ">> in module-begin" is printed only once, but the expansion
> >> of `m` fails, indicating a fresh store.
> >>
> >> This is troublesome for Typed Racket, which uses the store to record
> >> the types of identifiers. Is this the intended behavior?
> >> --
> >> sam th
> >> samth at ccs.neu.edu
> -- 
> sam th
> samth at ccs.neu.edu

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