[cffi-devel] `lambda-callback'

[James Bielman]

Lars Rune Nøstdal <larsnostdal at gmail.com> writes:

> I've been using this lately:
>
>   (defvar *lambda-callbacks* nil
>     "TODO: Clean up later somehow?")
>
>   (defmacro lambda-callback (return-type args &body body)
>     (let ((name (read-from-string (symbol-name (gensym)))))
>       `(progn
>          (defcallback ,name ,return-type ,args
>            , at body)
>          (push ',name *lambda-callbacks*)
>          (callback ,name))))
>
> ..maybe something like this could be included in cffi? :)

Using CFFI's DEFCALLBACK in any non-toplevel context is probably a
recipe for disaster on at least some of the Lisps we support, so I
don't think this can work as a portable solution.  (I don't understand
the purpose of *LAMBDA-CALLBACKS* or the READ-FROM-STRING business
either...)

I implemented a proof-of-concept CALLBACK-LAMBDA for SBCL and CLISP
awhile back---the patch should be in the list archives somewhere.  I'd
like to see it cleaned up and integrated into CFFI proper, but
currently don't have the time to finish it; the main things missing
are an interface for freeing the callback functions, and probably some
sort of CALLBACK-FLET type macro that can be used when the callback
function has dynamic extent.

James