Re: Getting GNAT to issue ARM error messages

[dewar@gnat.com]

In article <1999Feb10.073547.1@eisner>,
  Kilgallen@eisner.decus.org.nospam wrote:

> A compiler referring a
> newcomer to a page in the Ada95 reference manual could
> lead to confusion because of the way that book is
> written.


And just to clarify what Larry wrote above, this is not
in any way a criticism of the ADa 95 RM, just a comment
on its different stylistic approach. Clarity for
non-experts and precision for experts are often opposing
goals. There are several factors in this opposition:

1. Precision for experts usually requires a more formal
style that is less accessible for non-experts.

2. Precision requires considering marginal cases carefully
and thoroughly that may confuse non-experts.

3. Redundancy, that is so often helpful in explaining
things to non-experts, is a menace in a precise definition,
it can only lead to self-contradiction, and adds nothing.

4. In a formal definition, precise terminology, and the
style of depending on that terminology is an important
tool, but it can often confuse (an example: how many
non-expert users immediately understand that a generic
package is not a package, so a rule that applies to
packages does not [necessarily] apply to generic packages).

The viewpoint of the designers of Ada 95 was that the Ada
83 reference manual was insufficiently precise, and that a
more formal, more precise approach was desirable. This was
a controversial point, and remains moot (undecided and
arguable) in my opinion, but that's a separate issue from
the current one (whether to put RM references in messages).

One thing to remember here is that I was the one who
started the idea of putting RM references in messages. The
first compiler to do this was Ada/Ed, and at the time it
was an innovation. I am not aware of previous compilers for
other languages that contained references to the standard
in this manner (after all most programmers for other
languages don't even know a standard exists, let alone use
it as a standard reference source). Other Ada 83 compilers
copied this innovation from Ada/Ed.

So I certainly don't oppose the general idea, and indeed
the general idea is a good one, *if* the standard is
written in an aggressively accessible style. For the Ada
83 standard, I think this criterion was usually met. For
the Ada 95 standard, it makes better sense to decide on
a case by case basis if an RM reference is helpful.

That is why my suggestion is to consider individual
examples where an RM reference would be helpful, rather
than discussing the point as a general abstract issue.

Robert Dewar
Ada Core Technologies

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