Re: Foreign Callbacks

> Windows often uses callbacks. How can I call back into a Lisp function? I
> see define-foreign-callable, but the assumption seems to be that you're
> defining functions to be called from by name from a DLL...? To call back
> from Windows I'd need to pass some pointer-to-a-function, where the
> function declaration was defined by Windows itself. So ultimately I
assume
> that I need to get a pointer to the function defined by
> define-foreign-callable...?

(fli:define-foreign-callable ("lisp-wnd-func" :result-type :long)
        ((hWnd :hwnd) (Msg :ulong) (wParam :ulong) (lParam :long))
;your stuff here
)

(defvar *lisp-wnd-func* (fli:make-pointer :symbol-name "lisp-wnd-func"
:functionp t))

This is very old code, may be it's simpler now.

*** Thanks! I read the chapter on pointers, but it didn't mention this use
of make-pointer. But there was :functionp right in the reference...

> Also, just to check: I'm going to pass a Lisp object out which then gets
> sent back in from the callback. I don't want the object to be garbage
> collected while it's out in the wild. I can do that by making sure some
> Lisp thing points to it while it's held externally--but is there another
> way? Or should I be worried about something else...?

You don't pass a lisp object, you have to allocate a foreign object that
you
can pass to windows.

*** Thanks again. Going back through the manual, I was able to find an
example in section 2.4.2.