Re: RFC 63 (v3) Exception handling syntax

>>>>> "PRL" == Perl6 RFC Librarian <[email protected]> writes:

PRL> RFC 80 proposes standard exception classes and methods for core exceptions.
PRL> This RFC doesn't need to repeat those, but it can expound upon the
PRL> semantics that exception classes ought to have.  Assume wlog that they
PRL> all inherit from a base class, C<Exception>.  Some people think that
PRL> exceptions should not be rethrown implicitly.  We can provide a boolean flag
PRL> in the class or even the exception object itself to be checked for this:

PRL>      sub Exception::IO::implicit_rethrow { 0 }        # One class
PRL>      sub Exception::implicit_rethrow     { 0 }        # All classes
PRL>      throw Exception::Socket(implicit_rethrow => 0);  # Just this exception


PRL> [Note: it had been proposed that this functionality would be provided by a
PRL> method C<uncaught_handler> which would be called if an exception wasn't 
PRL> caught.
PRL> But if that routine decided to rethrow the exception, the C<continue> block
PRL> would not get called at the right time.]

Please include the comments about global variables and action at a distance.

PRL> =head2 Exception classes - ignoring

PRL> Note that we could also make it possible to selectively or globally ignore
PRL> exceptions, so that perl continues executing the line after the C<throw>
PRL> statement.  Just import a C<ignore> function that takes a class name:

PRL>      ignore Exception::IO;     # Ignore all I/O exceptions
PRL>      ignore Exception;         # Ignore all exceptions

PRL> and when perl sees the C<throw>, it just does nothing.  (Or do it by
PRL> overriding a base class method as for C<implicit_rethrow> if you don't want
PRL> to put another function in the namespace.)  Since C<throw> and C<die>
PRL> should be essentially identical, this would allow any kind of exception to
PRL> be ignored, not just the ones that were C<throw>n.  This is not necessarily
PRL> a good thing, of course.




Oh, no! Are you really suggesting that after

	open (FOO, "nonesuch") or throw "file not found"

The next statement continues??????

How in $DIETY's name do you expect to protect code?



PRL> =head2 $SIG{__DIE__}

PRL> <$SIG{__DIE__}> needs to be triggered only as a I<last> resort
PRL> instead of firing immediately, since it messes with the mind of this and
PRL> every other decent exception handling mechanism.  Perhaps it should be axed
PRL> altogether.  Please.




$SIG{DIE} should die. Action at a distance.  Global. Can't know what
other threads or modules want done here.


<chaim>
-- 
Chaim Frenkel					     Nonlinear Knowledge, Inc.
[email protected]				               +1-718-236-0183