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

From: Matthias Felleisen (matthias at ccs.neu.edu)
Date: Mon Jun 25 18:53:08 EDT 2012

Sam, can you focus on cases of submodules for which you can guarantee that #%module-begin is okay and reject others [with an explicit, informative error message]? -- Matthias

On Jun 25, 2012, at 6:47 PM, Matthew Flatt wrote:

> At Mon, 25 Jun 2012 17:50:27 -0400, Sam Tobin-Hochstadt wrote:
>> The problem (I
>> think) is that the implicit `require` of `(submod "..")` happens
>> *before* the expansion of `#%module-begin` inside the submodule.
> That's the same for a top-level module M whose initial language is some
> other module L, right? The require of `L' happens before the
> `#%module-begin' expansion in `M'... and it can't be any other way,
> because `#%module-begin' comes from `L'.
>> The
>> key bit of code is the residual snippet left in the outer module:
>>         (begin-for-syntax
>>             (when (unbox is-typed?)
>>               (set-box! type-env 1)))
>> Currently, in TR, the code in the begin-for-syntax is unconditional,
>> and therefore it gets re-run in the store used for expanding the inner
>> submodule.  However, if I add the `when`, then the `set-box!` doesn't
>> happen, and the expansion of `m` fails.  I'd like to be able to add
>> this conditional, so I'd like to change the order of effects slightly
>> here.
> I see what you mean, but I don't think it makes sense to change the
> order of things in the way that you're suggesting. I don't have any
> immediate ideas, but I'll think about it more.
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