[racket] Access scheme library from C

The easiest approach is often to put Racket in its own OS-level thread,
where scheme_main_setup() is given a function that receives evaluations
requests and sends back results.

Currently, I don't think it's possible to call into Racket, completely
leave, and call back in the way you suggest. You might imagine calling
scheme_set_stack_base() on each entry to reset the start of the stack
traversal on each entry, but that would create various problems with,
for example, Racket continuations or threads that are captured/started
in one scheme_set_stack_base() and applied/resumed in another.

At Mon, 02 Dec 2013 17:12:35 +0100, Daniel Langner wrote:
> Hello,
> 
> I want to embed the racket interpreter to create a C interface for a 
> certain r6rs scheme library. It comprises diverse functions which return 
> complex scheme objects. These, in turn, may be passed to other functions 
> within the library (and therefore shouldn't be gc'ed along the way).
> 
> I got it so far that I call scheme_main_setup, passing along my run 
> function which loads the library into the scheme environment and does 
> the actual scheme calls. This approach, however, isn't suitable for what 
> I want. When run returns, all is gone and gets garbage collected (I think).
> 
> I'd rather have a typical interface with an initialization function 
> (that loads the environment and returns normally), some wrapper 
> functions (which call scheme_dynamic_require and scheme_apply), and a 
> destructor function.
> 
> Probably I'd have to use scheme_set_stack_base rather than 
> scheme_main_setup. Obviously I would want to reuse the environment 
> throughout all calls. There hopefully is a way to prevent the garbage 
> collector from collecting it, and also the other scheme objects which my 
> library returns.
> 
> My question is: is this feasible? How would I go about it? Thanks for 
> your help!
> 
> Regards,
> Daniel
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