Re: Required Metrics

["Robert I. Eachus" <rieachus@earthlink.net>]

Robert Dewar wrote:
 
> Not till the ARG ruled clearly on this issue, and the AVO
> backed it up with the tests (which as I mention above, I
> helped write), in ACVC version 1.10, did a proper set of
> tests get written.

   I have no disagreement with what Robert Dwer wrote here (hmmm
enthusiastically agree?  applaud wildly?).  However, the Chapter 13
tests which RBKD wrote had less effect on Ada 95
than he and others including myself hoped, for several reasons.

   First, by the time some of these were required by the ACVC vendors
were all working
on Ada 9X compilers and were unwilling to make fundamental changes not
required by Ada 9X.

   Second, the conformance rules were changed to allow compilers not to
comply with up to ten tests, as long as the intent was to correct these
in the next validated version.  In practice, since most new tests in
1.10 and after were chapter 13 tests, it allowed vendors to be much more
agressive in stating that "this cannot be 'simply' implemented in this
compiler."  Of course, in many cases this was exactly right--it was the
tests that would have required major compiler changes that didn't get
made.

   Finally, since many of the Chapter 13 tests were, in effect, pushed
back by challenges to later ACVC versions, some of these tests were
never effectively required.  Since the design of Ada 9X started well
before ACVC 1.10 affected production compilers, the experience of users
during the early phases of the Ada 9X development process was with
compilers that in some cases  did not take representation clauses, etc.
seriously.

   So as Robert Dewar points out, while the requirements in Ada 95 are
much more clearly spelled out, they are definitely a subset of what was
finally required in Ada 83.  (Fortunately, the marketplace has tended to
require this 'additional' support in any case.  I hope 'de facto'
becomes 'de jure' with the next Ada standard...
 
> Interesting -- I had COMPLETELY forgotten this
> statement in the standard. It is of course an exact codification
> of some of the things that Bob Duff and I have argued. In
> particular, it provides an absolutely CLEAR basis for Bob Duff's
> observation that the behavior of the delivered binary compiler
> code, and the behavior of code generated by this compiler
> constitute documentation in the sense of the RM.
> 
> So the RM *did* try to define what documentation meant, and
> came up with something about as far from what Ken has in mind
> as one can imagine.
 
    Yes, the intent was to prevent documentation requirements from
limiting actual implementations.  In Ada 83, the ACVC tests effectively
required every Ada compiler to implement a "usable" maximum input line
length.  And the blasted ACVC tests checked that the compiler DID NOT
accept longer lines, whle requiring that you accept an identifier that
was the same length as a line.  So you had to set an arbitrary maximum
line length and enforce it even if in the absence of the ACVC test the
limit would only be imposed by memory size or file characteristics.  In
Ada 95 the requirement concerning line length is in RM 2.2(15): "...The
maximum supported line length and lexical element length are
implementation defined."  (The minimum for each is 200 characters.)