Re: how to use ffi-help

[Matt Wette]

On 12/30/18 10:07 AM, Amirouche Boubekki wrote:

> 1. Is it possible to have a program or subcommand of guild that
>    does take a header file from stdin and prints the bindings to stdout.
This could be done.  I will think about it.

> 2. What do you think of PSSI https://github.com/ktakashi/r6rs-pffi
This seems like the functionality of Guile ffi API and the scheme-bytestructure 
package.
I don't see a reason to port the FH to PSSI at this point.

> 3. is it possible to specify a 'renamer' procedure that takes as argument
>    a symbol representing the kind of thing (enum, member, static 
> variable,
>    struct, typdef, function, constant macro...) and the original name 
> of the
>    original name of the thing. The goal here is to allow to have 
> schemey variable
>    names.

The syntax of define-ffi-module provides a #:renamer form that takes a 
procedure to
reform symbols.  I don't think I have implemented it.  This is on my list.

> 4. In the module definition, is it possible to add some code that will 
> be appended
>    to the generated file?

Yes.  I do this all the time.  Please see one of the examples in 
nyacc/examples/ffi,
like for glib.ffi shown below.  You can also specify C declarations using the
#:api-code form.  See example below.

(define-ffi-module (ffi glib)
  #:pkg-config "glib-2.0"
  #:include '("glib.h")
  #:inc-filter (lambda (file-spec path-spec)
                 (or (string-contains path-spec "glib/" 0)
                     (string=? file-spec "<glibconfig.h>")))
  )

(define-public G_PI (ffi-glib-symbol-val 'G_PI))
(define-public G_PI_2 (ffi-glib-symbol-val 'G_PI_2))
(define-public G_PI_4 (ffi-glib-symbol-val 'G_PI_4))
...


(define-ffi-module (hack)
  #:api-code "double sqrt(double);")
=>
(define-module (hack)
...
;; double sqrt(double);
(define sqrt
  (let ((~sqrt (delay (fh-link-proc
                        ffi:double
                        "sqrt"
                        (list ffi:double)
                        hack-llibs))))
    (lambda (arg-0)
      (let ((~arg-0 (unwrap~float arg-0)))
        ((force ~sqrt) ~arg-0)))))
(export sqrt)
...

> 5. In the module definition, is it possible to declare the interface 
> of the generated
>    module?

I'm not sure what you mean, but for

  (define-ffi-module (ffi glib) ...

the generated module is

  (define-module (ffi glib) ...

Is this what you are asking for?

Matt