Re: Towards a reasonable unwinding flow-control semantics.

[Tony Olekshy]

Graham Barr wrote:
> 
> On Wed, Aug 16, 2000 at 10:19:53AM -0400, Chaim Frenkel wrote:
> >
> > I would say that outside of the try block all throws are caught if
> > at all by the wrapping try. So that throws propogate outward. Never
> > back within itself.
> 
> Agreed.

Throws propagate *forward* through the try clauses, then *outward*
if not cleanly caught.  We're not proposing any notion of throws
propagating *inward*.

> > There is one case to be considered, what if the try block wishes
> > to avoid its own catch clauses, and start the unwinding with the
> > uplevel try block.
> 
> Can you think of a time you would want that ?

And even if you did, don't you just want something like this:

    try {
        $avoidCatches_JustUnwind = predicate();
        }
    except { $avoidCatches_JustUnwind } => catch { throw }
    .
    . Other catch clauses go here, and are attempted only
    . if $avoidCatches_JustUnwind is false after try.
    .
    finally {
        # Can't be avoided. Don't use this clause otherwise.
        }

Yours, &c, Tony Olekshy