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Date: Sun, 09 Dec 2007 23:40:20 +0100
From: Georg Bauhaus <rm.tsoh+bauhaus@maps.futureapps.de>
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Subject: Re: Exceptions
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Date: 2007-12-09T23:40:24+01:00
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Robert A Duff wrote:
> Simon Wright <simon.j.wright@mac.com> writes:
> 
>> I think this would be a very bad idea. I don't want to be forced to
>> deal with the exception 'here' when it would be better handled by my
>> caller.
> 
> But this would only apply to some exceptions.  If you don't want to be
> "forced", use an unchecked exception.
> 
> I think there are some mistakes in the Java design for exceptions, but I
> don't think the whole idea of exception contracts is bad.
> 
> - Bob

When Robert Dewar talked about exceptions at MIT (I think, that's
from memory of a video recording), one of his arguments was that
you don't want to write cascades of conditionals for handling
return values (being either returned values or failure indicators)
---because that's a mess.

Now, when we have a sequence of statements in a block,

   P1(X); P2(X); ... ; Pn(X, Y);

then what will be the average number of exception handlers
for this block? Involving how many different exceptions?
We would soon arrive at a complicated roughly O(N) size comb
of exception choices and Pk-exceptions covered in each handler.
Each handler possibly involving conditionals for Pk's and Pj's.
I see this as a likely consequence once Ada people start trying
to formally cover the exceptional.

How would that be an improvement and not just the return code
mess again?

(And it smells of using state machines to once again try
to apply AI to things we didn't think of.)