type checks (was: CLISP typed foreign references)

Von: Kevin Rosenberg wrote:

> Thanks for the detailed information. I'll reread the 
> imp-notes for CLISP and think about your message. I would
I think it doesn't mention the properties of FOREIGN-ADDRESS etc. objects.

> Looking at foreign-variable and foreign-address, perhaps I
> can plug in my own malloc and free to allocate arbitrary 
> objects outside of a function call.

Don't do malloc+free, I'll do. I'm already thinking about WITH-ALIEN/STACK-ALLOCATION for CLISP. I already have a MALLOC hack (but no free yet).

The problem to me, however, is not malloc+free. It's matching C type information between foreign objects and function signatures. So far, I don't seem forward to implementing C subtype style testing in Lisp.

OTOH, if I declare (function GETENV (* char)) and pass a typeless foreign pointer (or worse, an integer like in ACL), I'm even less safe than working in plain ANSI-C. I don't like that.

Any ideas?

(C-subtypep '(c-ptr (c-array character <N>)) 'c-string) ->?
(C-subtypep 'c-string '(c-ptr-null (c-array-max character <N>))) ->?
(C-subtypep '(c-array-ptr character) 'c-string) ->?

Worse-is-better => provide version which does no checking so people can start working, then think about improvements and a better world.

BTW, thanks for putting my draft of an article on FFI design on the server.

Regards,
	Jorg Hohle.