From: George Ogata <g_ogata@...>
Date: 2004-03-19T04:24:35+09:00
Subject: Re: `#catch'ing many symbols

"Robert Klemme" <bob.news@gmx.net> writes:

> I don't think so.  Problem is that catch returns the instance associated
> with the throw and when catching multiple symbols you can't distinguish
> what happened.  In that case a single symbol is enough because you can use
> the returned element to carry information about the event:

Thanks, I'd forgotten about the second throw arg.  I guess that
satisfies the uncondtional case.  Conditional was really the one I was
interested in, though.

> Conditional catch does not make sense IMHO.  What do you want to
> achieve with that?

I think it can be useful in recursive scenarios.  To unwind the stack
to the first call, you catch the symbol only if it's the first
invocation.

In my case, I have a stackable command interpreter interface
("stackable" in the sense that you can recursively invoke one while
one is running, like the way you sometimes nest shells).  One command
exits just the topmost layer to return to the one below.  Another
exits the whole stack.

To implement this, the former command throws :done, the latter :quit.
Only the bottom-most interpreter catches :quit, the others just catch
:done.

I suppose there're few uses for multi-catching though, so fair enough.
If it's a harmless extension, though...