Re: question on exceptions

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

Robert Dewar (dewar@merv.cs.nyu.edu) wrote:
: Bob Duff says

:> "By the way, during the design of Ada 9X, it was suggested that we have
:> functions for querying things like the Current_Exception_Name and
:> Current_Exception_String.  However, the design team rejected this idea
:> for the reasons explained above -- presumably the semantics of calling
:> these at the wrong time would be "erroneous", which is bad.  

: I see no reason why these could not be functoins which can only be called
: within a handler, checked statically by the compiler. This is how GNAT
: implements the DEC Current_Exception package (which has these semantics).

There would still be some possible ambiguities associated with such 
functions.  What are their semantics when there is an exception raised and 
then handled in some statement within the handler, but preceding 
the call to one of these special functions?  Does it report the
most recent exception raised, or does it report the exception being
handled by the current handler?  Also, what happens if you rename
such a subprogram?  Does the renaming retain its special status?

I presume we generally agree that having a namable exception 
occurrence object makes the semantics clearer, and gives the
programmer a bit more flexibility.

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