[racket] TR: struct: #:prefab option

On 2013-05-06 10:09:06 -0400, Ray Racine wrote:
>    The below is now failing for me.
>    (struct: Stuff ([this : String][that : Natural]) #:prefab)
>
> [...]
>
>    If there is a typing issue with the use of #:prefab and its banishment
>    permanent, is there an alternate best practice mechanism for easy struct:
>    serialization/de-serialization?

If you're using the Racket pre-release, then that was probably my commit
that broke that. Sorry for breaking compatibility here, but it's unsound
for TR to admit #:prefab as is. Here's an example:

  $ racket
  Welcome to Racket v5.3.
  -> (module foo typed/racket
       (struct: foo ([f : (Float -> Float)]) #:prefab)
       (define x (foo (lambda: ([x : Float]) (* 3.3 x))))
       (provide x))
  -> (module bar racket
       (require 'foo)
       (struct foo (f) #:prefab)
       ((foo-f x) "foo"))
  -> (require 'bar)
  2.293305645053357e-309

The first module exports a #:prefab struct instance containing an
optimized (Float -> Float) function. Since it's a prefab, the second
module (which is untyped), can freely access the function stored inside.

Since the function is unprotected, it does an unsafe multiplication on a
string and no contract error is raised.

I'm not sure what's a good alternative for serialization in TR off the
top of my head.

Cheers,
Asumu