[GAP Forum] The Add function

[Hebert Pérez-Rosés]

OK, thank you very much. I would just swear that I had already tried that.
Cheers,
Hebert.


2011/1/8 Keshav Rao Kini <krkini at ntu.edu.sg>

>  Hello,
>
> Each time you use Add, it adds perm as a new list entry in out. It does NOT
> add the current value of perm as a new list entry in out, but rather inserts
> a reference to the list perm. The list perm is added to the list out three
> times, and by the time the function returns, perm = [1,2,3], so out consists
> of three [1,2,3].
>
> If you want to remember previous states of a list, you'll always need to
> make a copy, because this is not done automatically when using functions
> like Add. Try using for example the ShallowCopy function.
>
> Hope that helps.
>
> Yours,
>     Keshav
>
> Disclaimer: the boilerplate text at the foot of this email has been added
> automatically by my mail server. This was not done by my request (rather the
> opposite) so please disregard it.
>
>
>
> 2011/1/8 Hebert Pérez-Rosés <hebert.perez at gmail.com>
>
>> Dear all,
>>
>> I'm embarrased to say this, but I'm very puzzled by the behaviour of the
>> Add
>> function. I have this simple test code:
>>
>> --------------------------------------
>>  TestFun:= function(n)
>>   local perm, out, i;
>>
>>   out:= [];
>>   perm:= [];
>>   for i in [1..n] do
>>       perm[i]:=0;
>>   od;
>>   for i in [1..n] do
>>       perm[i]:= i;
>>       Add(out, perm);
>>   od;
>>   return out;
>>  end;
>> ----------------------------------
>>
>> If I now make a call to Test(3), I should get [ [1,0,0], [1,2,0], [1,2,3]
>> ],
>> right? However, I'm getting [ [1,2,3], [1,2,3], [1,2,3] ]. Do you get the
>> same thing? Can anybody explain to me what's happening here?
>>
>> Thank you very much in advance,
>>
>> Hebert Perez-Roses
>> The University of Newcastle, Australia
>> _______________________________________________
>> Forum mailing list
>> Forum at mail.gap-system.org
>> http://mail.gap-system.org/mailman/listinfo/forum
>>
>
>
> ------------------------------
> CONFIDENTIALITY: This email is intended solely for the person(s) named and
> may be confidential and/or privileged. If you are not the intended
> recipient, please delete it, notify us and do not copy, use, or disclose its
> content. Thank you.
>
> Towards A Sustainable Earth: Print Only When Necessary
>