[ruby-core:56349] Re: [CommonRuby - Feature #8723] Array.any? predicate returns true for empty array.

Some more explanation reading on the subject - and reasons for this:
http://en.m.wikipedia.org/wiki/Universal_quantification

http://en.m.wikipedia.org/wiki/Vacuous_truth

It's a basic classic logic definition.
On Aug 3, 2013 5:02 AM, Martin J. Dst <[e-mail]> wrote:

> On 2013/08/03 15:40, nurettin (Nurettin Onur TUGCU) wrote:
>
>>
>> Issue #8723 has been updated by nurettin (Nurettin Onur TUGCU).
>>
>>
>> I find I need to address all the questions
>>
>
>  However I find the result needs not be defined. Also, defining "all?" or
>> "any?" makes no sense for empty set since they will never execute.
>>
>
> You say:
>
> > Also, defining "all?" or "any?" makes no sense for empty set since they
> will never execute.
>
> So should be write code like
>
> unless enum.empty?
>    enum.all { |x| predicate(x) }
> end
>
> Think about this in a bigger context. Assume we are applying .any or .all
> not to a simple array, but to an array of arrays.
>
> We would e.g. write
>
> arrays.all { |a| a.all { |x| predicate(x) } }
>
> If we use what we currently have in Ruby, this just works, even if there
> are some empty lists in the 'arrays' array. With your proposal, we'd have
> to write a lot of special code.
>
>  ============
>>
>> Of course I understand that there are other languages which do this the
>> same, I also understand that it would break existing code, and I know that
>> docs are clear, and of course I can write my own, but is it really correct
>> behavior to treat undefinedness as truth? In my opinion, no.
>>
>
> It would be incorrect behavior to treat undefinedness as truth, but the
> results of these operations are not undefined. They have a clear underlying
> mathematical background. People familiar with this area know what the
> results are, and they expect them to work the way they do. Anything else
> would be highly confusing for everybody except maybe beginners.
>
> I suggest you read some introductory book in this area (discrete math). An
> alternative is to read a book on Haskell, especially one that discusses
> code transformations/equivalences and proofs.
>
> Regards,   Martin.
>
>