[e-lang] Exception types and ejector patterns (was Re: Remaining semantic issues)

[Kevin Reid]

On Jul 22, 2006, at 21:07, Mark S. Miller wrote:

> In order to make your ejSwitch idea above work, the ejector  
> argument might get thrown, and so must be the kind of thing that  
> could be, or be included in, an exception. Given this constraint, I  
> suppose it may as well be an exception. On E-on-Java, it would  
> currently be hard to enable E programs to define new exception  
> types. But if we decide that's the right thing, we could certainly  
> do it.

E-on-CL has essentially the same problem (CL:CONDITION =  
java.lang.Throwable), and as a workaround it defines a generic  
condition class with properties defined at creation time. See tests/ 
exception-data.updoc.

Further, I see no reason we couldn't define a condition/Throwable  
that's a forwarding wrapper around an arbitrary E object.

> Once an exception is thrown, I remain skeptical about whether it  
> would then be useful and robust to dispatch on its type.

Debugging. Last-resort failure handling ("what do I tell the user  
went wrong?").

-- 
Kevin Reid                            <http://homepage.mac.com/kpreid/>