On Tue, Aug 15, 2000 at 06:23:57PM -0600, Tony Olekshy wrote:
> Jonathan Scott Duff wrote:
> >
> > What's wrong with just using the switch statement? It seems
> > like except and catch are becoming special-purpose switches
> > to me. Is it really necessary?
>
> It's not necessary, but it is the whole point of it all.
>
> Try is "just" a special-purpose if, except is a special-purpose
> else if, catch is a special-purpose else, as is finally. Breaking
> the local flow of control in a program is itself special purpose.
>
> The special-purposeness is that these constructs have unwind
> semantics.
[ snip ]
> Also note that with manual implementation of exception handling,
> you don't get any unwind-time trace-back debugging info either,
> which RFC 88 does for you. When you start using this a lot (and
> you will, if Perl 6 goes to internal exceptions for fatal errors),
> you'll quickly find you're glad to have this "special purpose"
> information.
Okay, imagine something for me:
# some code here that may cause an exception
exceptions { # when thrown, we end up here
switch ($@->^_) {
case canFoo { ... } # caught if canFoo
case isa('IOError') { ... }
case isa('MathError') { ... }
throw $@; # rethrow unhandled
}
}
This "exceptions" block is only entered if an exception is thrown in the
current lexical scope. Inside the exceptions block we have access to the
exception via $@ and access to the "unwinding information" via some other
special variable that I haven't given a name yet as I'm not exactly
sure what you mean :-) New keywords added: "throw" and "exceptions".
Semantics supported: ignore unhandled or not (those that wish to
ignore unhandled exceptions just omit the C<throw> at the end of the
switch.)
Now, in the interest of continuing my education, what did I leave out?
:-)
-Scott
--
Jonathan Scott Duff
[EMAIL PROTECTED]
