Re: Compiler implementation of speciallized needs annexes.

[dewar@gnat.com]

In article
<36D3A1EF.E7CA2A8C@physics.BLAH.purdue.BLAH.edu>,
  "Robert T. Sagris" <robs@physics.BLAH.purdue.BLAH.edu>
> wrote:
> I was wondering why only GNAT implements all of the
> specialized needs annex's. All of the other vendors I
> looked into implement A, B as they are required. C and D
> are also generally implemented by everyone. Rational also
> implements G.

Actually you should check VSR's carefully, a lot of
compilers do NOT fully implement annex D (for example,
as far as we know, GNAT is the only compiler that fully
implements annex D on VxWorks, including a full
implementation of FIFO_Within_Priorities dispatching
policy.)

> Is this do to a lack of customer demand for these
> features or is it something else?

It is not so much a "lack of customer demand". Rather
it is an issue of how much customer demand there is
compared to the cost of implementation.

Implementing annex E for instance is a very large task,
and one that may well not be justified by customer demand.
GNAT certainly has a number of customers for annex E, but
if the decision had been a purely commercial one, who
knows?

In fact we decided very early on in the GNAT project that
we would implement all the annexes. This decision was made
even before ACT existed, and was part of the commitment of
the GNAT project to providing a *complete* freely available
Ada 95 system.

Since our first validation was for all the annexes, we
decided that we would go for 100% validations on all
targets. That has not always been easy, but it makes for
a consistent guarantee of completeness. Of course not every
annex is required in every situation, and that is why it is
perfectly practical to use compilers that lack annex
features that you do not need. This was after all the whole
point of defining optional special needs annexes in the
first place. For example, the Intermetrics compiler for the
Patriot 2 certainly does NOT need the Information Systems
annex (Patriot missiles are not in the habit of performing
payroll computations as they fly through the air :-)

That being said, it would definitely be nice to see some
other compilers implement some of the "missing" annexes.
For one thing, it would be interesting to see if different
compilers implementing Annex E could really communicate :-)

Most certainly every vendor is driven by customer demand,
so if you see something that is not implemented, then
it is definitely likely to mean that>

> I was just wondering
>
> Robbi Sagris
>

Robert Dewar
Ada Core Technologies

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