Thats the sort of logic that makes me wary of exceptions.
Wary of exceptions as they are usually implemented, that is.
I like the failure model that SNOBOL and Icon use. They're a bit like miniature exceptions: if some function or operator doesn't have a value to return, it fails. Failure simply means "it didn't work". Catching it can be done explicitly with constructs like if and while, or implicitly which produces back-tracking and goal-directed evaluation (this should be familiar to RE wizards). If it isn't handled, it propagates upwards until it is or it can't go up anymore (letting something fail for the side-effects is a known programming technique in Icon). It removes the problem of "handling it elsewhere" that try/catch can produce.
OTOH, exceptions have some features that failure doesn't. The obvious one is that different types of exceptions can be raised. Failure is just failure. There are some system functions that have to fail when there's a problem; but you have to call another function to see how and why they failed.
(A less-obvious feature of exceptions is that they have much larger scope than failure. In Icon, failure is often bounded, so that a statement with an uncaught failure doesn't cause the language to backtrack farther than it should. This is by design. Exceptions have to play games with the stack as they propagate up until something catches them.)
Whether something is an error or not in a failure model is somewhat easier to answer: is there a value to return? No? Okay, fail*. As far as I can tell from this discussion, exceptions are *just* unwieldy enough that it actually becomes an issue as to whether a function, faced with a problem, should say "that's an error - throw an exception" or "no, that's not really an error - no exception needed." :-) Ouch.
Wade.
* To be fair, even Icon doesn't follow this slavishly. There are some - mainly graphcis - functions which return &null for one condition and "" for its opposite. It turns out that in actual usage, this is more versatile, particularly as there are operators to quickly and directly turn &null or not-&null into failure.
