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Re: dispatching on keywords

There is an interesting Ph.D. dissertation that is relevant to the
discussion of error values.  It is by Andrew Black, out of Oxford, and
is titled "Exception Handling: the Case Against."  I don't have it
with me, but it came out sometime in the early 1980s.

The paper looks at, and classifies, a number of different proposed
exception handling mechanisms.  It makes a distinction between
exception handling (anticipated problems) and fault recovery
(unanticipated problems) (my terminology is probably off...), and goes
on to argue that the combination of first class procedures and "oneof"
(tagged union) values covers all of the interesting cases.  It also
attacks the argument that explicit exception handling constructs make
code clearer by showing that the idea of an "exceptional" case is
often ill-defined.

I can't really summarize the paper since it has been quite a few years
since I read it, but it struck me as being well written and well reasoned.

-- Jim Mayer
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