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From: rossiter@svax.cs.cornell.edu (David G. Rossiter)
Newsgroups: net.lang
Subject: Re: Escape structures (retitled)
Message-ID: <270@svax.cs.cornell.edu>
Date: Wed, 9-Apr-86 15:31:11 EST
Article-I.D.: svax.270
Posted: Wed Apr  9 15:31:11 1986
Date-Received: Mon, 14-Apr-86 03:23:04 EST
References: <1187@mmintl.UUCP> <6925@cca.UUCP> <7040@cca.UUCP>
Reply-To: rossiter@svax.UUCP (David G. Rossiter)
Organization: Cornell Univ. CS Dept, Ithaca NY
Lines: 33

Richard Harter writes:
>
>	Another thought is that the whole problem of exception
>handling is a mess.  C's setjmp/longjmp mechanism is no more than
>a "here is a low level primitive for the job -- you figure out
>how to do it yourself" approach.  The PL/I ON condition handlers
>are only a small cut above C.  It seems to me that the whole area
>of error handling is in need of major theoretical analysis.
>
>		Richard Harter, SMDS Inc.

There is an *excellent* theoretical and practical analysis of error
handling in a recent PhD thesis by Andrew P. Black, from Balliol
College of Oxford University, UK.  The title is "Exception Handling:
the case against", submitted January 1982.  Black is now at Univ. of
Washington, I believe.  I have a copy of the thesis which I obtained
from the chairman of my PhD committee; I'm not sure where it is publically
available.  One could presumably email to Black.

Anyway, he examines in detail exception handling mechanisms in producation
languages like PL/I, Algol W, Algol 68, Mesa, and Ada, as well as in
academic (but implemented) languages like CLU.  He concludes that the
way to think of so-called "exceptions" is as named constituents of a
discriminated union data type (sort of like Pascal variant records, but
type secure).  It's very clean semantically and seems easy to program in
and write compilers for.  If there's more interest I can post the abstract
and summary.



David Rossiter / CS Dep't / Cornell University / Ithaca / NY / 14850 / USA
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