[racket] users Digest, Vol 114, Issue 3

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-------- Original message --------
From: users-request at racket-lang.org 
Date:02/02/2015  11:00 AM  (GMT-06:00) 
To: users at racket-lang.org 
Cc:  
Subject: users Digest, Vol 114, Issue 3 

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Today's Topics:

   1. Re: forward pointer declarations (Anthony Carrico)
   2. Re: forward pointer declarations (Sam Tobin-Hochstadt)
   3. Re: forward pointer declarations (Anthony Carrico)


----------------------------------------------------------------------

Message: 1
Date: Mon, 02 Feb 2015 08:02:43 -0500
From: Anthony Carrico <acarrico at memebeam.org>
To: Matthew Flatt <mflatt at cs.utah.edu>
Cc: racket Users <users at racket-lang.org>
Subject: Re: [racket] forward pointer declarations
Message-ID: <54CF7573.6060000 at memebeam.org>
Content-Type: text/plain; charset="utf-8"

On 02/02/2015 01:17 AM, Matthew Flatt wrote:
> It's also valid to reference `wl_interface-pointer` directly:
...
> 
> I don't have a nicer solution if you want to refer to
> `_wl_message-pointer`, though.
> 

The forward reference is actually in wl_message, like this:

(define-cstruct _wl_message
  ((name _string/utf-8)
   (signature _string/utf-8)
   (types (_cpointer 'wl_interface))))

(define-cstruct _wl_interface
  ((name _string/utf-8)
   (version _int)
   (method_count _int)
   (methods _wl_message-pointer)
   (event_count _int)
   (events _wl_message-pointer)))

I ended up just inlining (_cpointer 'wl_interface) for the forward
reference. This ends up creating two (_cpointer 'wl_interface) ctypes,
but it's no problem, correct?

I don't think it is possible to "reference 'wl_interface-pointer'
directly" as you suggest in this case because of the "cannot reference
an identifier before its definition" error.

-- 
Anthony Carrico


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Message: 2
Date: Mon, 02 Feb 2015 14:04:25 +0000
From: Sam Tobin-Hochstadt <samth at cs.indiana.edu>
To: Anthony Carrico <acarrico at memebeam.org>, Matthew Flatt
<mflatt at cs.utah.edu>
Cc: racket Users <users at racket-lang.org>
Subject: Re: [racket] forward pointer declarations
Message-ID:
<CAK=HD+bSzeuvOm+pjuM53MfidOfy6=mJC0M7KwSjDJ7qj3LwGQ at mail.gmail.com>
Content-Type: text/plain; charset="utf-8"

Maybe a ctype which is a delay node, along the lines of
'recursive-contract', is the right thing here.

Sam

On Mon, Feb 2, 2015, 8:05 AM Anthony Carrico <acarrico at memebeam.org> wrote:

> On 02/02/2015 01:17 AM, Matthew Flatt wrote:
> > It's also valid to reference `wl_interface-pointer` directly:
> ...
> >
> > I don't have a nicer solution if you want to refer to
> > `_wl_message-pointer`, though.
> >
>
> The forward reference is actually in wl_message, like this:
>
> (define-cstruct _wl_message
>   ((name _string/utf-8)
>    (signature _string/utf-8)
>    (types (_cpointer 'wl_interface))))
>
> (define-cstruct _wl_interface
>   ((name _string/utf-8)
>    (version _int)
>    (method_count _int)
>    (methods _wl_message-pointer)
>    (event_count _int)
>    (events _wl_message-pointer)))
>
> I ended up just inlining (_cpointer 'wl_interface) for the forward
> reference. This ends up creating two (_cpointer 'wl_interface) ctypes,
> but it's no problem, correct?
>
> I don't think it is possible to "reference 'wl_interface-pointer'
> directly" as you suggest in this case because of the "cannot reference
> an identifier before its definition" error.
>
> --
> Anthony Carrico
>
>
> ____________________
>   Racket Users list:
>   http://lists.racket-lang.org/users
>
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------------------------------

Message: 3
Date: Mon, 02 Feb 2015 09:41:46 -0500
From: Anthony Carrico <acarrico at memebeam.org>
To: users at racket-lang.org
Subject: Re: [racket] forward pointer declarations
Message-ID: <54CF8CAA.60500 at memebeam.org>
Content-Type: text/plain; charset="windows-1252"

Along these lines, I also am a little foggy on unions. This:
  http://docs.racket-lang.org/foreign/C_Union_Types.html

says, "Unions are always treated like structs." But I have no idea what
that phrase means. I don't get the impression that unions have tags like
structs can have. Or can they? Maybe any pointer can be tagged? For example:

(define _wl_argument
  (_union _int32
          _uint32
          _wl_fixed
          _string/utf-8
          (_cpointer/null 'wl_object)
          _uint32
          _wl_array-pointer
          _int32))

Now suppose I need to pass an array of _wl_argument. Does it even make
sense to use a tag in the _cpointer?

(define _wl_argument-pointer (_cpointer 'wl_argument))

(define-wl-client wl_proxy_marshal_array_constructor
  (_fun #:save-errno 'posix
        _wl_proxy-pointer
        _uint32
        _wl_argument-pointer
        _wl_interface-pointer
        -> _wl_proxy-pointer/null
        ))

So as I said, I'm just a little foggy on some of the concepts, but I do
think the FFI is very nice. Maybe I'm just trying to use stronger typing
than actually exists in the ffi. I've started reading
Eli Barzilay/Dmitry Orlovsky "Foreign Interface for PLT Scheme".

-- 
Anthony Carrico


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End of users Digest, Vol 114, Issue 3
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