Subject: Re: The origins of CL conditions system
From: (Rob Warnock)
Date: Tue, 04 Dec 2007 22:18:24 -0600
Newsgroups: comp.lang.lisp
Message-ID: <>
Daniel Weinreb  <> wrote:
| In a separate point, I do not think that an exception
| is necessarily only used for an error (a bug).  To
| my mind, there are lots of appropriate places to
| use exceptions as an expected and proper part of the
| running of a program.  Exceptions are how a function
| or method reports an "unusual result", such as an
| "open file" reporting "file not found".  Very often
| a program knows perfectly well that a file might
| not be found and is designed to behave a certain way
| when that happens (e.g. prompt the user for a filename,
| if this is an interactive application).  There's nothing
| at all wrong with coding this as an exception; in fact
| there's a lot to be said for it.

Kent Pitman's 2001 paper makes the same point:
    Condition Handling in the Lisp Language Family
    Condition Systems vs Error Systems
    The Common Lisp community typically prefers to speak about its
    condition system rather than its error system to emphasize that
    there are not just fatal but also non-fatal situations in which
    the capabilities provided by this system are useful.

| One of these days I will write an essay on my view of
| exceptions and post it on my blog at

Oops! Then maybe I shouldn't have mentioned Kent's paper!  ;-}


Rob Warnock			<>
627 26th Avenue			<URL:>
San Mateo, CA 94403		(650)572-2607