Re: What is wrong here? (Generic and controlled types)

[Robert Dewar <robert_dewar@my-deja.com>]

In article <38FFFDEE.431A@li.net>,
  Vincent Marciante <marciant@li.net> wrote:
> Robert Dewar <robert_dewar@my-deja.com> writes:
>
> |    29.    package Real_Vectors is new Generic_Vectors(Real,
Index,
> Zero);
> |           |
> |        >>> instantiation error at generic_vectors.ads:23
> |        >>> controlled type must be declared at the library
level
> |        >>> instantiation error at generic_vectors.ads:75
> |        >>> controlled type must be declared at the library
level
>
> > P.S. it is hard to see how the GNAT message could be any
> > clearer, suggestions welcome!
>
> 29.    package Real_Vectors is new Generic_Vectors(Real,
Index, Zero);
>        |
>     >>> instantiation error at generic_vectors.ads:23
>
>     >>> controlled type must be declared in a package
>                                          ^^^^^^^^^^^^
>     >>> that is a library unit
>     ^^^^^^^^^^^^^^^^^^^^^^^^^^
>
> Both "package" and "library unit" are in the ARM's index.


Well so is "library level", and if we are going to use technical
terms in the error messages we might as well use them
accurately. A library level package is definitely NOT the same
thing as a package that is a library unit, so your replacement
is inaccurate.

I don't mind considering replacing the formal correct existing
message with an informal message that might not be quite as
correct but is more informative, but surely it is not a good
idea to replace it with a message using formal terms that is
just wrong :-)

The fact that something is in the index of the RM is really
not good enough for two reasons:

1. There is no reason to expect beginning programmers to have
the RM, and indeed every reason to expect them NOT to have it.

2. If they do have it, sending them off to the index of this
document is often not likely to be as helpful as you think.

But you can see the bind of choosing such messages, I suggested
that the very familiar term "global" might be better, but
Florian thinks that is equally obscure.

Probably for really difficult messages like this you want an
auxiliary wizard that can provide additional information at an
appropriate level of sophistication -- we have envisioned such
a tool for some time. I even have had a name for it which I
thought up 8 years ago, GNOME - GNAT On-line Message Explainer.
Of course we delayed too long implementing it, and now we can't
use that name, so now we don't even have a name :-(


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