Path: news.cs.au.dk!not-for-mail
From: nospam2159@cs.au.dk (Peter von der =?iso-8859-1?q?Ah=E9?=)
Newsgroups: comp.lang.beta
Subject: Static vs. dynamic exceptions
Date: 20 Jun 2000 11:51:16 +0200
Organization: Computer Science Department of the University of Aarhus
Lines: 57
Message-ID: <yc0hfaoptnv.fsf_-_@ufleku.cs.au.dk>
References: <20000619173848.8485.qmail@noatun.mjolner.dk> <8im02p$8s5j$1@xinwen.cs.au.dk>
NNTP-Posting-Host: ufleku.cs.au.dk
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
X-Trace: xinwen.cs.au.dk 961494676 214029 255.255.255.255 (20 Jun 2000 09:51:16 GMT)
X-Complaints-To: news@cs.au.dk
NNTP-Posting-Date: 20 Jun 2000 09:51:16 GMT
X-Attribution: Ahe
User-Agent: Gnus/5.0806 (Gnus v5.8.6) Emacs/20.6
Xref: news.cs.au.dk comp.lang.beta:12451

>>>>> "JLK" == Jorgen Lindskov Knudsen <jlk@cs.au.dk> writes:

 JLK> Just because the BETA exception model is not identical to the
 JLK> C++/Java exception handling model, does not imply that there is
 JLK> none :-)

This is true.  I just did not remember/know the terms static and
dynamic exceptions.

It does seem to me that every modern language support some kind of
dynamic exceptions.  It appears as if the reason for BETA only[1]
supporting static exceptions is that leave and restart are limited
(statically?/lexically?) in the Mjolner implementation.

Are the limitations to leave and restart justified in the original
language definition, or were they chosen because they were the most
easily implemented?

/Peter

                                 ****

[1] Look at dynamic vs. static exceptions.  It should be clear that
dynamic exceptions can simulate static exceptions:

try
(#
   catch::(# (* handle syntaxerror *) #)
do getint -> i
#)

which simulates:

getint(# syntaxError::(# (* handle error *) #) #) -> i

You could even write (might not be correct, but you should get the
idea):

-- streamlib: attributes --
getIntStaticEx:
  (#
     syntaxError:< exception;
     i: @integer
  do
     try
       (#
          catch::
            (# do (if e // syntaxerror then syntaxError if) #)
       do getInt -> i
       #)
   exit i
   #)

I do not believe that it is possible to simulate dynamic exceptions
with static exceptions and if this is true one could say that dynamic
exceptions is a proper superset of static exceptions.  Please prove me
wrong.