Steel Bank Common Lisp

Hi everyone,

When I started using Lisp, I received a lot of help on this mailing
list regarding foreign interfaces in SBCL.  I use foreign functions
quite frequently, yet I like to use native Lisp arrays whenever
possible, thus I created the FFA library to hide the plumbing
necessary for foreign interfaces.

A lot of the code in FFA was created to work around the fact that
sb-sys:vector-sap doesn't work for simple-arrays that have a rank
higher than 1.  Currently the workaround is to create a simple array
of rank 1, and then displace to this when I need multidimensional
arrays.

I am about to redesign FFA, and I would like to ask if there is a
chance of getting this limitation removed, ie have sb-sys:vector-sap
work on array of rank higher than 1, or the introduction of another
function that would allow this.  I know little of SBCL's internal
workings, is there anything that makes this impossible, or tricky, or
is it just that no one has asked for it yet?

Thanks,

Tamas

On Fri, Nov 28, 2008 at 10:25 PM, Tamas K Papp <tkpapp@...> wrote:

> A lot of the code in FFA was created to work around the fact that
> sb-sys:vector-sap doesn't work for simple-arrays that have a rank
> higher than 1.  Currently the workaround is to create a simple array
> of rank 1, and then displace to this when I need multidimensional
> arrays.
>
> I am about to redesign FFA, and I would like to ask if there is a
> chance of getting this limitation removed, ie have sb-sys:vector-sap
> work on array of rank higher than 1, or the introduction of another
> function that would allow this.  I know little of SBCL's internal
> workings, is there anything that makes this impossible, or tricky, or
> is it just that no one has asked for it yet?

In SBCL a multidimensional simple-array has an underlying
one-dimensional simple-array which holds the data. You can access it
like so (though this is not officially supported, but support for it
could possible be added.)

(defun simple-array-vector (array)
  (declare (simple-array array))
  (if (sb-kernel:array-header-p array)
      (sb-kernel:%array-data-vector array)
      array))

(simple-array-vector (make-array '(3 3) :initial-contents '((1 2 3) (4
5 6) (7 8 9))))

Cheers,

 -- Nikodemus

On Sat, 29 Nov 2008 15:57:50 +0200, Nikodemus Siivola wrote:

> On Fri, Nov 28, 2008 at 10:25 PM, Tamas K Papp <tkpapp@...> wrote:
> 
>> A lot of the code in FFA was created to work around the fact that
>> sb-sys:vector-sap doesn't work for simple-arrays that have a rank
>> higher than 1.  Currently the workaround is to create a simple array of
>> rank 1, and then displace to this when I need multidimensional arrays.
>>
>> I am about to redesign FFA, and I would like to ask if there is a
>> chance of getting this limitation removed, ie have sb-sys:vector-sap
>> work on array of rank higher than 1, or the introduction of another
>> function that would allow this.  I know little of SBCL's internal
>> workings, is there anything that makes this impossible, or tricky, or
>> is it just that no one has asked for it yet?
> 
> In SBCL a multidimensional simple-array has an underlying
> one-dimensional simple-array which holds the data. You can access it
> like so (though this is not officially supported, but support for it
> could possible be added.)
> 
> (defun simple-array-vector (array)
>   (declare (simple-array array))
>   (if (sb-kernel:array-header-p array)
>       (sb-kernel:%array-data-vector array)
>       array))
> 
> (simple-array-vector (make-array '(3 3) :initial-contents '((1 2 3) (4 5
> 6) (7 8 9))))

Thank you, this is exactly what I was looking for.

If feasible, please make this officially supported, and let me know when 
it is, will then release the new version of FFA.

Thanks,

Tamas