Re: Exception types?

[dewar@merv.cs.nyu.edu (Robert Dewar)]

<<> The proposal was in the mapping, but was removed. Maybe someone who
> participated actively in the language design can tell us why ?
>>


There was a LOT of stuff in the mapping documents. There was virtually
unanimous agreement (with only the design team dissenting) that in
aggregate the design was far too extensive. So it had to be cut back.
This feature in particular was one that introduced a lot of implementation
complexity for insufficient gain, and there was general agreement that
it had too low a value-to-effort ratio. Note that this does not mean
that in isolation this feature was "bad" (there is nothing wrong per se
with the last straw on the camel's back :-)

Note that I think the general level of change turned out about right. Most
(but still not all) Ada vendors have managed to upgrade to Ada 95 (GNAT
acted as a useful nudge). We still have at least one vendor remainin
committed to Ada 83, and one major vendor that dropped out completely
(Digital) and one of the reasons for that dropout was (as Bevin has
noted), the extent of the change. We also had one Ada technology drop
out of site (the old Alsys technology) as a direct result of the fact
that the change was too extensive.

SO I think we compromised at a reasonable level. We lost some implementations
but kept the majority. If we had accepted everything in the mapping team's
design document, I think we would have far fewer Ada 95 compilers on the
market today (perhaps none).

That being said, at this stage, it is very worthwhile to go back and look
at some of the (very good) suggestions that were dropped. Another example
of a feature worth looking at for example is the extension of 'Class to
non-tagged types. There are many others.

At this stage, it would be definitely interesting on a research project
basis to attempt adding some of these features to experimental versions
of GNAT (this is one of the advantages of having the sources available!)