Re: Ada.Execution_Time

[Robert A Duff <bobduff@shell01.TheWorld.com>]

"Randy Brukardt" <randy@rrsoftware.com> writes:

> They're supposed to provide a useless implementation that raises Use_Error 
> for most of the operations. There are a pair of Notes to that effect 
> (A.16(129-130)).

OK, good enough.

>... I don't think features should ever be designed so that 
> implementations have to appeal to 1.1.3(6) - my preference would be that 
> that paragraph not exist with the language itself sufficiently flexible 
> where it matters.

But something like 1.1.3(6) has to exist in every language definition,
at least implicitly.  Computers are finite machines, so there will
always be things that are "impossible or impractical", and it is
impossible for any language designer to predict what that means
in all cases.

>...(Otherwise, implementations could leave out anything that 
> they want and appeal to 1.1.3(6).

Well, not really.  That para says "given the execution environment", not
"given the compiler-writer's whim, or laziness, or lack of interest".
One could claim that "if X = 0..." is impractical to implement, but of
course people would laugh at that claim.

>... I think that both interfaces and 
> coextensions are "impractical" to implement for the benefit gained, so does 
> that mean I can ignore them and still have a complete Ada compiler??)

I definitely disagree about interfaces.  I might agree about
coextensions, depending on my mood on any particular day of the week.
But yeah, you can implement what you like, and claim it's an Ada
compiler.  Whether people buy it is a question that lies outside any ISO
standard.

Standards are optional!  The Ada standard doesn't require anybody to do
anything.  Still, there's a community that can decide, informally, that
so-and-so compiler is an implementation of Ada 2005 (despite a few minor
bugs), and such-and-such compiler is not.

- Bob