Re: RISC

[Charles Hixson <charleshixsn@earthlink.net>]

Robert A Duff wrote:

> "Marin David Condic" <marin.condic.auntie.spam@pacemicro.com> writes:
> 
>> Its hard to come up with absolute rules since it often requires
>> subjective, artistic judgements. Just keep in mind that the intention is
>> to have a mechanism that deals with *errors* - not anticipated conditions
>> that can be accommodated with some sort of "normal" processing.
> 
>....
> Another way to look at it is that the point of exceptions is to separate
> the code that *detects* errors from the code that *handles* those
> situations.  If the code that detects something knows what to do about
> it, then exceptions aren't necessary -- that code can just have an 'if'
> statement that checks the condition, and handles the situation in the
> 'then' part.
> 
> - Bob
> 

Is the problem that exceptions are expensive, or that exceptions violate 
localization?  Or something else?

E.g.:  Should EOF detection be done with an exception?  It's usuaual, but 
expected.  I think of encountering an EOF and an unusual condition, and 
it's nice to be able to automatically check for it whenever a read happens 
without explicitly calling on an eof() function.

Java rather expects that procedures will throw exceptions.  I don't know 
C++ well enough to comment.  Python seems to believe that exceptions are 
quite reasonable.  Eiffel thinks that exceptions should be handled within 
the same routine that defines them. Etc.  I think that this is a language 
specific issue.

My impression was that Ada exceptions were intended to handle unusual cases 
(exceptional cases).  That they were slightly more expensive to raise than 
a local branch would be, but that they were slightly cheaper if no 
exceptional case was detected.  And that they should be handled as close to 
the routine that raised them as possible.  Preferably within the routine.  
But I would hardly call myself an expert at Ada.