Path: news.cs.au.dk!not-for-mail
From: "Jorgen Lindskov Knudsen" <jlk@cs.au.dk>
Newsgroups: comp.lang.beta
Subject: Re: Static vs. dynamic exceptions
Date: Tue, 20 Jun 2000 23:14:05 +0200
Organization: University of Aarhus, Department of Computer Science (DAIMI)
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Peter,

You are really spot on here.

The model for integrating dynamic and static exception handling in BETA is
essentially along the same lines as the proposal.  However, there are some
nitti-gritty details more to consider :-)

Regards,
Jørgen


Peter von der Ahé wrote in message ...
>>>>>> "JLK" == Jørgen Lindskov Knudsen <jlk@mjolner.dk> writes:
>
> JLK> There is no connection between leave/restart and static
> JLK> exception handling - these two issues have been discussed and
> JLK> designed separately (look e.g. at [ref1] or the chapter in the
> JLK> BETA book).
>
>The only connection is that I'm pretty sure that I could implement
>dynamic exceptions in BETA if leave/restart wasn't so limited.  I'm
>also thinking about closures and call/cc as known from scheme.  But
>maybe this is a bit far fetched for BETA :-)
>
>[...]
>
> JLK> Thus, 'simulation' isn't sufficient - could you on the other
> JLK> hand implement an abstraction with the necessary semantics,
> JLK> etc., we would be in another ballgame.
>
>This was just to "prove" that at least dynamic exceptions is a
>superset of static exceptions (maybe not a proper superset).
>
>But let me try harder.  I might even come up with something that you
>could use in BETA :-)
>
>If static exceptions is a subset of dynamic exceptions it should be
>possible to extend static to dynamic:
>
>Lets say that we have the well known exception pattern and a try
>pattern.  Normally when an uncaught/unbound static exception occurs we
>end up with a runtime error.  (In my experience most of the errors in
>the Mjolner tools are unbound exceptions.)
>
>One way to add dynamic exceptions to BETA could be to let try patterns
>catch unbound exceptions, that is:
>
>try
>  (#
>     catch::(# (* handle second exception *) #)
>  do
>     getInt(# syntaxError::(# (* handle first exception *) #) #);
>     getInt (* a second exception can occur here *)
>  #)
>
>To fully implement this the exception pattern should be aware of the
>nesting level of try blocks and be able to call the catch methods in
>all the try blocks on the stack until one handles the exception.
>
> JLK> However, whether static and dynamic ex.handling is a choice
> JLK> between models, or both are needed is an open question right now
> JLK> - actually this very subject was discussed at the Workshop on
> JLK> Exception Handling at the ECOOP'2002 conference last week.
> JLK> Currently, my conception is that both mechanisms have their
> JLK> merit (for slightly different purposes), perhaps warrenting
> JLK> having both (actually a very preliminary design exists for
> JLK> BETA).
>
>I'm looking forward to this.  Would it be possible to see this
>preliminary design?
>
>--
>YMMV