Re: Mixing syntax-rule and indentifier-syntax

2012-01-18 Thread Andy Wingo 
On Wed 18 Jan 2012 00:26, Tobias Brandt  writes:

>> 0. I'm sure there is another way, but my mind blanks at the moment
>
> After you got me started, I was able to simplify and generalize it a bit.
> (-> is a GOOPS generic accessor I defined elsewhere. It works with
> vectors, arrays, strings, etc ...)
> (define-syntax with-accessors  (lambda (stx)    (syntax-case stx ()
>   ((_ (id ...) exp ...)       #`(begin           #,@(let (;; checks if

My eyes!!!

;-)

Can you repost, but without having your editor wrap the lines?

Thanks :)

Andy
-- 
http://wingolog.org/

Re: Accessing multiple values from C

2012-01-18 Thread Andy Wingo 
On Wed 18 Jan 2012 04:15, Mark H Weaver  writes:

> Should this verify that `obj' is a values object?
>
> Should it verify that `idx' can fit in an inum?

Agreed!

> Also, if `obj' is _not_ a values object and `idx' is 0, should this
> simply return `obj'?  Since a single value is conceptually no different
> than multiple values (but is represented very differently within Guile),
> I'd think that this function should handle that case gracefully.

Hum, good question.  I'm inclined to agree.

Regards,

Andy
-- 
http://wingolog.org/

Re: Accessing multiple values from C

2012-01-18 Thread Ludovic Courtès 
Hi Mark,

Mark H Weaver  skribis:

> Julian Graham  writes:
>> +SCM
>> +scm_c_value_ref (SCM obj, size_t idx)
>> +{
>> +  SCM values = scm_struct_ref (obj, SCM_INUM0);
>> +  return scm_list_ref (values, SCM_I_MAKINUM (idx));
>> +}
>> +
>
> Should this verify that `obj' is a values object?
>
> Should it verify that `idx' can fit in an inum?

Yes, good point.  Using an ‘SCM_VALIDATE’, which will throw an exception
upon error, right?

> Also, if `obj' is _not_ a values object and `idx' is 0, should this
> simply return `obj'?

Yes, makes sense to me.

Julian: could you change these bits and send an updated patch?

Thanks,
Ludo’.

Re: Accessing multiple values from C

2012-01-18 Thread Julian Graham 
Hi all,

Thanks for the review!

On Wed, Jan 18, 2012 at 3:19 PM, Ludovic Courtès  wrote:
> Julian: could you change these bits and send an updated patch?

Will do.


Regards,
Julian

Re: Accessing multiple values from C

2012-01-18 Thread Mark H Weaver 
l...@gnu.org (Ludovic Courtès) writes:

> Mark H Weaver  skribis:
>
>> Julian Graham  writes:
>>> +SCM
>>> +scm_c_value_ref (SCM obj, size_t idx)
>>> +{
>>> +  SCM values = scm_struct_ref (obj, SCM_INUM0);
>>> +  return scm_list_ref (values, SCM_I_MAKINUM (idx));
>>> +}
>>> +
>>
>> Should this verify that `obj' is a values object?
>>
>> Should it verify that `idx' can fit in an inum?
>
> Yes, good point.  Using an ‘SCM_VALIDATE’, which will throw an exception
> upon error, right?

Well, there's a complication with using an `SCM_VALIDATE' to check for
values objects.  If `idx' is 0 (make sure it's exact!), then we must
_not_ throw an exception if `obj' is not a values object.  However, in
that case we still need to know whether `obj' is a values object or not.

Also, a fine point about desirable error messages: asking for `idx' 5 of
a values object with only 3 elements is, conceptually, the same kind of
error as asking for `idx' 5 of something that is _not_ a values object.

Therefore, I think in both cases the error should be something to the
effect of "too few values".

Thanks,
  Mark

Re: Accessing multiple values from C

2012-01-18 Thread Ludovic Courtès 
Hi!

Mark H Weaver  skribis:

> l...@gnu.org (Ludovic Courtès) writes:
>
>> Mark H Weaver  skribis:
>>
>>> Julian Graham  writes:
 +SCM
 +scm_c_value_ref (SCM obj, size_t idx)
 +{
 +  SCM values = scm_struct_ref (obj, SCM_INUM0);
 +  return scm_list_ref (values, SCM_I_MAKINUM (idx));
 +}
 +
>>>
>>> Should this verify that `obj' is a values object?
>>>
>>> Should it verify that `idx' can fit in an inum?
>>
>> Yes, good point.  Using an ‘SCM_VALIDATE’, which will throw an exception
>> upon error, right?
>
> Well, there's a complication with using an `SCM_VALIDATE' to check for
> values objects.  If `idx' is 0 (make sure it's exact!), then we must
> _not_ throw an exception if `obj' is not a values object.  However, in
> that case we still need to know whether `obj' is a values object or not.

Yes, I already agreed on this one.  ;-)

> Also, a fine point about desirable error messages: asking for `idx' 5 of
> a values object with only 3 elements is, conceptually, the same kind of
> error as asking for `idx' 5 of something that is _not_ a values object.
>
> Therefore, I think in both cases the error should be something to the
> effect of "too few values".

Right.

Ludo’.

Re: Accessing multiple values from C

2012-01-18 Thread Mark H Weaver 
I think something along these lines be ideal,
though this code is UNTESTED.

 Mark


SCM
scm_c_value_ref (SCM obj, size_t idx)
{
  if (SCM_VALUESP (obj))
{
  SCM values = scm_struct_ref (obj, SCM_INUM0);
  size_t i = idx;
  while (SCM_LIKELY (!scm_is_null (values)))
{
  if (i == 0)
return SCM_CAR (values);
  values = SCM_CDR (values);
  i--;
}
}
  else if (idx == 0)
return obj;

  scm_error (scm_out_of_range_key,
 "scm_c_value_ref",
 "Too few values in ~S to access index ~S",
 scm_list_2 (obj, scm_from_unsigned_integer (idx)),
 scm_list_1 (scm_from_unsigned_integer (idx)));
}

Re: Accessing multiple values from C

2012-01-18 Thread Mark H Weaver 
At Julian's request, I went ahead and pushed my implementation of
`scm_c_value_ref' to the stable-2.0 branch, so it will be in 2.0.4.

Thanks,
  Mark