Webmaster Forum / Perl / General Perl Topics / July 2009

I'm iworking on a patch for Perl 5 that implements the Perl 6 closure
traits (ENTER/LEAVE/...) as special blocks. There are several details
that aren't clear to me from either S04 or the spec tests; I apologize
if these have been discussed before, as I haven't been following p6l.
I'm also not subscribed, so if people could keep me in the CC that would
be appreciated.

- Presumably when an exception is thrown through a block, the LEAVE and
 POST queues are called (in that order). What if a PRE block fails: is
 the POST queue on the same block called? (Do you have to satisfy your
 post-conditions even if your pre-conditions failed?)

- If a POST block is called as a result of a thrown exception, and it
 fails, which exception 'wins'?

- Presumably if an ENTER block dies, the rest of that ENTER queue is
 abandoned. Does that also apply to the LEAVE queue? What should

   {
       LEAVE { say "leave1" }
       LEAVE { say "leave2"; die "foo"; }
   }

 print? Similarly POST: once one post-condition has failed, are
 subsequent post-conditions checked?

- Can a try block catch an exception thrown from its own ENTER or LEAVE
 queue? For example in this case:

   try {

       try {
           ENTER { die "foo" }
           CATCH { default { say "caught inside" } }
       }

       CATCH { default { say "caught outside" } }
   }

 which CATCH block gets the exception? What about PRE/POST: can you
 CATCH failure of your own pre-/post-conditions?

- Does it make any difference in any of the above if 'die' is replaced
 by 'exit'?

Ben