Returning errno as a second value

[Felix Filozov]

I have a with-errno
<https://github.com/ffilozov/cffi/tree/with-errno>implementation.


On Wed, Aug 14, 2013 at 5:23 PM, Felix Filozov <ffilozov at gmail.com> wrote:

> Ah, I understand why it has to be dynamic now. I'll start working on
> with-errno then.
>
> The consing problem is clearer now, but I wonder how much overhead it adds
> compared to the cost of making a foreign call. According to the Allegro CL
> documentation, a foreign call which returns errno is less efficient. For
> other Lisps, an additional foreign call would have to be made to get errno.
> Maybe consing is negligible?
>
>
> On Wed, Aug 14, 2013 at 3:04 PM, Luís Oliveira <luismbo at gmail.com> wrote:
>
> Felix Filozov <ffilozov at gmail.com> writes:
>>
>> > Maybe we can even do this using lexical binding, since GET-ERRNO could
>> > be a macro that expands to a lexical variable introduced by
>> > WITH-ERRNO.
>>
>> The issue there is that foreign-funcall will be setting errno.
>>
>>
>> > Could you elaborate where there's a consing issue, if errno is
>> > returned as the last, or first, value?
>>
>> So, the pseudo-code for the implementation in foreign-funcall would be
>> something like:
>>
>>   (multiple-value-bind (return-value errno)
>>       (%foreign-funcal ...)
>>     (let ((translated-return-values (multiple-value-list
>> (translate-from-foreign ...))))
>>       (values-list (cons errno translated-return-values))
>>       ;; or (values-list (nconc translated-return-values (list errno)))
>>       ))
>>
>> Right now I'm inclined to discard all but the first translated return
>> value. (This is your initial solution, isn't it?)
>>
>> Luís
>>
>>
>>
>
> On Wed, Aug 14, 2013 at 3:04 PM, Luís Oliveira <luismbo at gmail.com> wrote:
>
>> Felix Filozov <ffilozov at gmail.com> writes:
>>
>> > Maybe we can even do this using lexical binding, since GET-ERRNO could
>> > be a macro that expands to a lexical variable introduced by
>> > WITH-ERRNO.
>>
>> The issue there is that foreign-funcall will be setting errno.
>>
>>
>> > Could you elaborate where there's a consing issue, if errno is
>> > returned as the last, or first, value?
>>
>> So, the pseudo-code for the implementation in foreign-funcall would be
>> something like:
>>
>>   (multiple-value-bind (return-value errno)
>>       (%foreign-funcal ...)
>>     (let ((translated-return-values (multiple-value-list
>> (translate-from-foreign ...))))
>>       (values-list (cons errno translated-return-values))
>>       ;; or (values-list (nconc translated-return-values (list errno)))
>>       ))
>>
>> Right now I'm inclined to discard all but the first translated return
>> value. (This is your initial solution, isn't it?)
>>
>> Luís
>>
>>
>>
>
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