Re: Improving Ada Exceptions

[stt@houdini.camb.inmet.com (Tucker Taft)]

For what it is worth, we proposed during the Ada 9X revision 
allowing more flexibility in the exception mechanism, allowing for a 
hierarchy of exceptions, treating exception declarations approximately
like type declarations, and treating "raise" statements
approximately like creating an instance of the exception type.

At the time, it was felt to be overkill.  I suspect there might
be more sympathy for it today, though if you look at how exceptions
are used, many of them are used to represent unanticipated errors rather 
than anticipated messages to be received by higher level code.  

Java has an interesting approach, where some classes of exceptions
are presumed to be unanticipated errors (and no local handler or "throws"
clause is required), whereas others are required to have local handlers, or
a "throws" clause that announces that the exception might be propagated.
Unlike in C++, these rules are enforced at compile-time, which
seems much more useful.

--
-Tucker Taft   stt@inmet.com   http://www.inmet.com/~stt/
Intermetrics, Inc.  Burlington, MA  USA