On Wed, Sep 28, 2005 at 09:49:11 -0700, Larry Wall wrote: > I'd like to add a little more. The context of the original throw > probably knows best whether it's even possible or sensical to > continue, so it should be optional whether the exception contains a > resume continuation. The presence of the continuation signals that > the inner code would *like* to continue but can't figure out how > without more dynamic context, where that could even include human > interaction on some level. The absence of a resume continuation > means someone thinks this dynamic branch needs a wooden stake through > its heart. > > But thinking about optional continuations, another thing occured > to me. It's always bugged me that warnings were something different > from exceptions, and now I think we can unify them, if we say that > a warning is simply an exception with two properties. The first is > that it's in a category that, by default, the outermost runtime will > just report on and resume. And the second is, of course, that the > resume continuation is required. So turning any warning into a > fatal error consists of stripping the resume continuation. (Which > might mean that the presence of the continuation is what differentiates > warnings from fatal errors, but I doubt it. There needs to be a > class of exceptions that have a resume continuation that is not resumed > by default. A "die" should throw that kind of exception, and have > a reasonably expectation of not being resumed in the normal course of > things.
So CATCH does set the &*EXCEPTION_HANDLER continuation to be something
like:
given $! {
when Exception::ResumesByDefault {
old_exception_handler($!);
}
... # the body of the CATCH
}
and
> or have a WARN block of its own, I don't know.
Or maybe &*EXCEPTION_HANDLER is a multi-method-continuation.
CATCH could simply be a macro that compiles to
ENTER {
temp &*EXCEPTION_HANDLER := &*OUTER::EXCEPTION_HANDLER;
&EXCEPTION_HANDLER.add_variant(cont (Exception::Fatal $!) {
};
}
BTW, how do we declare continuations explicitly? Or is it just a sub
that is directly .goto'd ?
An MMD exception handler that is extended in the dynamic scope is
cool because it's not limitied to just control exceptions, warnings,
and fatal errors.
Some fun definitions:
every loop construct creates some lexical bindings in the body:
&next - throws an Exception::Control::Next
&redo - throws an Exception::Control::Redo
...
Entering the loop adds temporary variants to
&*EXCEPTION_HANDLER:
multi cont (Exception::Control::Redo) {
body.goto(*$current_binding_tuple);
}
multi cont (Exception::Control::Next) {
...
}
--
() Yuval Kogman <[EMAIL PROTECTED]> 0xEBD27418 perl hacker &
/\ kung foo master: /me climbs a brick wall with his fingers: neeyah!
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