Re: Gnat GPL 2010 available soon (conditional expressions)

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Tue, 6 Jul 2010 09:31:05 -0700 (PDT), Phil Clayton wrote:

> The concept of an order is important because the function F could have
> side effects in the above example (though I would not advocate that as
> good practice).

AFAIK, presently the order is not defined. So though this is legal

   X : String (1..80) := (others => Character'Read (Stream'Access));

It is not a good idea.

> However, we would be able to write
> 
>   (for I in reverse A'Range => A(I))
> 
> to represent the reverse of the array A is perhaps a little confusing.

The effect is undefined. Theoretically the compiler could initialize array
elements concurrently on a multi-core processor.
 
> Also, it really only makes sense to have one variable holding the
> array index.  For example, if we could write
> 
>   (I, J : 1 .. 5 => ...)
> 
> surely I and J would always be equal: there are only 5 elements in the
> array.  Having
> 
>   (for I in 1 .. 5 => ...)
> 
> syntactically rules out multiple variables.

Yes, but many other things as well. However I prefer an absolutely
different approach anyway, e.g. proper index types. In my world a diagonal
would be initialized like:

   (Diagonal (5, 5) => 1.0, others => 0.0)

where Diagonal is a proper function.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de