ffcall

[Clark McGrew <mcgrew@ale.physics.sunysb.edu>]

Hi, 

This is a naive question.  Is there any particular reason people seem
to prefer libffi to ffcall?  

I'm only familiar with ffcall, and it seems OK.  I have some code that
does essentially the same thing as the libffi module, but I've never
got around to packaging it.  I've used it (along with some code to get
direct access to C pointers) to hack directly at the lowest levels of
Xt.

Cheers,

Clark

PS: The ffcall web page is:
	 <http://clisp.cons.org/~haible/documentation/ffcall>

PPS: Part of the reason I haven't tried to contribute this is that the
module system is a little up in the air and I was never sure where the
compiled guile modules belonged.  Discussing this on the list really
helped.  

PPPS: As far as I can see, the only advantage ffcall has to ffi is that
you can create a callback for C directly in scheme.  For example:

	(define c-callback
		(callback 
			(lambda (a b) (+ a b))
			'int
			'(int int)))

makes c-callback a pointer to a function with a C prototype: 

	int afunc(int, int);

which will execute "(lambda (a b) (+ a b))".

If there is a C function that needs a callback, then you can use your
scheme directly:

	void c_needs_a_callback(int (*func)(int,int)) {
		int i = func(1,2);
	}

calls "(lambda (a b) (+ a b))" from deep in side a C library without
knowing about guile (assuming func holds the address returned by
"callback").