Re: rfc: array literals

  This message is in MIME format.  The first part should be readable text,
  while the remaining parts are likely unreadable without MIME-aware tools.

---58492207-1917855976-1252624754=:478
Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed


FYI, this change is now implemented.

Note that Yann's version of test0 and the original version
of test0 (below) now behave differently (intentionally so).

I have attached a little script with examples you may run
to see the new behavior.

Ralf


On Fri, 12 Dec 2008, Yann LeCun wrote:

> Even though the behavior of "static" variables is semantically well
> defined, it's true that this particular behavior is a bit confusing
> (like the behavior of defvar which most people expect to work like
> setq or defparameter).
>
> The semantic of the code below is exactly like:
>
> (defparameter some_random_name [0 0 0 0 0])
> (defun test0 ()
>   (for (i 0 3)
>     (let ((v some_random_name))
>       (v 0 (+ (v 0) 1))
>       (printf "%f " (v 0)) ))
>   (print) )
>
> The proper way to fix this is to make array literal create a new
> matrix every time, and return it.
>
>  -- Yann
>
>
> On Friday 12 December 2008, Ralf Juengling wrote:
>> Hello,
>>
>> Consider this code, which exhibits a malicious bug.
>>
>> (defun test0 ()
>>    (for (i 0 3)
>>      (let ((v [0 0 0 0 0]))
>>        (v 0 (+ (v 0) 1))
>>        (printf "%f " (v 0)) ))
>>    (print) )
>>
>> ? (test0)
>> 1 2 3 4
>> = ()
>>
>> The desired output is "1 1 1 1". If I remember correctly,
>> somewhere in the documentation array literals are advertised
>> as a means to simulate something like "static variables" in
>> C. But here it does not square with the semantics of let.
>>
>> In my opinion, this is behavior will be confusing to many
>> users and we should change it in Lush2. When compiled, v
>> should simply be allocated on the stack when it is not returned
>> (and dynamically otherwise).
>>
>> Ralf
>>
>> ---------------------------------------------------------------------------
>> --- SF.Net email is Sponsored by MIX09, March 18-20, 2009 in Las Vegas,
>> Nevada. The future of the web can't happen without you.  Join us at MIX09
>> to help pave the way to the Next Web now. Learn more and register at
>> http://ad.doubleclick.net/clk;208669438;13503038;i?http://2009.visitmix.com
>> / _______________________________________________
>> Lush-devel mailing list
>> [email protected]
>> https://lists.sourceforge.net/lists/listinfo/lush-devel
>
>
>
>
---58492207-1917855976-1252624754=:478
Content-Type: TEXT/PLAIN; charset=US-ASCII; name=test-let.lsh
Content-Transfer-Encoding: BASE64
Content-ID: <[email protected]>
Content-Description: 
Content-Disposition: attachment; filename=test-let.lsh
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---58492207-1917855976-1252624754=:478
Content-Type: text/plain; charset="us-ascii"
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit
Content-Disposition: inline

------------------------------------------------------------------------------
Let Crystal Reports handle the reporting - Free Crystal Reports 2008 30-Day 
trial. Simplify your report design, integration and deployment - and focus on 
what you do best, core application coding. Discover what's new with 
Crystal Reports now.  http://p.sf.net/sfu/bobj-july
---58492207-1917855976-1252624754=:478
Content-Type: text/plain; charset="us-ascii"
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit
Content-Disposition: inline

_______________________________________________
Lush-devel mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/lush-devel

---58492207-1917855976-1252624754=:478--