[wg11] EXPRESS (DERIVEd) attribute redeclaration question

[Alan R Williams]

On 01/06/2012 21:27, Lothar Klein wrote:
> It has been always this way.

I agree.

> And the classical example is that if an entity A has an explicit
> INTEGER attribute and two subtypes B and C. In B the attribute is
> redeclared to be an odd number and in C to be an even number and there
> is an entity D that is a subtype of both, B and C then all this is
> valid Express. But it is not possible to construct a valid instance of
> D because you won't find an integer value that is both an odd and an even
> number simultaneously.

There was a prototype tool written (I think) in Scheme that detected 
some of these impossible combinations. I remember it found some 
interesting implicit features of the VHDL language.

> Lothar

Alan