The way this works, the box doesn't have to "get into" any modules
that aren't typed. Instead, when expanding a module A, that module
may contain uses of identifiers defined in a typed module T. Those
identifiers are macros that look something like this:
(define-syntax (id stx) (if typed-context? #'typed-id #'id-for-untyped))
Furthermore, the typed-context? value is initially set to #f, and it's
set to #true only inside the typechecker. When `id` is used in an
untyped module, it never gets set to #true, and so the
`id-for-untyped` is used. That means that the untyped code doesn't
need to know or do anything to make the system work, which is
necessary for Typed Racket to be a library.
There's more detail about this in our Scheme Workshop paper, here:
https://www2.ccs.neu.edu/racket/pubs/scheme2007-ctf.pdf
Sam
On Wed, Oct 7, 2020 at 6:18 AM Nate Griswold <[email protected]> wrote:
>
> I just finished reading the paper "Languages as Libraries", which really
> helped as an introduction to racket's language system (i had previously been
> ignoring the syntax features).
>
> I did have one question from it, which wasn't quite made clear in the
> interoperability section, or so it seems: how does the box `typed-context?`
> get into the modules that are not part of that language? Or more generally
> how would you solve this problem of needing to know which language of a
> module you are in without modifying the other languages? I was wondering if
> it was a hackaround or if there was a way to do generically in any language i
> might make.
>
> I grepped the source code and it looks like it's even exposed to the user in
> a function `syntax-local-typed-context?`, but i noticed that module never
> actually imports `typed-context?`.
>
> I suppose if it is a hack i could just reflect on the namespace to solve the
> problem, but i thought i would send a mail here to check.
>
> Thanks for the great work everyone!
>
> Nate
>
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