[plt-dev] certificates, #%module-begin, and typed-scheme's soundness

From: Jon Rafkind (rafkind at cs.utah.edu)
Date: Wed Dec 16 18:46:57 EST 2009

On 12/16/2009 04:37 PM, Sam TH wrote:
> On Wed, Dec 16, 2009 at 6:05 PM, Carl Eastlund<carl.eastlund at gmail.com>  wrote:
>> On Wed, Dec 16, 2009 at 5:19 PM, Sam TH<samth at ccs.neu.edu>  wrote:
>>> The program at the end of this message behaves in arbitrary ways.  In
>>> particular, it segfaults on my system.  However, this should be safe:
>>> Typed Scheme is checking that only vectors are passed to `f'.  But the
>>> `cheater' macro uses `local-expand' to extract a reference to `f', and
>>> use it in arbitrary ways.
>> You provided 'f'.  Certificates do not protect identifiers that are
>> provided from the module that defines them.
> As Jay points out, I didn't really provide `f'.  I provided a
> rename-transformer that points to `f'.  Here's a more explicit version
> of the original module:
> (module m typed/scheme
>    (require scheme/unsafe/ops (for-syntax scheme/base))
>    (: f ((Vectorof (U)) ->  Any))
>    (define (f x) (unsafe-vector-length x))
>    (define-syntax f*
>      (make-rename-transformer #'f))
>    (provide (rename-out [f* f])))
> This suggests to me that this is a bug in the interaction of
> rename-transformers and certificates.

I don't have an answer, but it seems to me that since you are providing 
*something* that the thing you provided can be inspected by destructing 
the syntax. Whether the syntax-case gets the original f or f* won't the 
result be the same? (the result being applying the function `f' to 3).

Or are you saying that since `f' was not provided that 
`make-rename-transformer' should not certify access to the syntax being 

Posted on the dev mailing list.