I was listening to the recent IO conversation on p6c, and decided to look at
IO.pm in rakudo. I immediately saw a bit of code that worried me:
try {
?$!PIO.close()
}
$! ?? fail($!) !! Bool::True
Why is that so cumbersome? That seems like one of the most obvious use-cases
for exceptions.
I looked over the synopses and tested some theories, but what I came to was
inconclusive. It seems like:
return try { die "oops" }
has undefined behavior because the return value of try is not clearly
spelled out (one might expect it to be the return value of the statement,
but that's not said anywhere, though it's backhandedly implied by an example
where try is used like do). Right now, the above causes a Null PMC access in
Rakudo, but that might just be a limitation in the implementation, rather
than an indication that try is not intended to have a return value.
I'd like to suggest that try's semantics should be defined and clearly
stated in S04/"Other do-like forms" as:
Try returns either the block's normal return value or the relevant, unthrown
exception.
Thus the above IO example becomes (with no changes in the grammar):
try { ?$!PIO.close(); Bool::True }
The golfer in me wants ? to take an adverb that causes this to all be moot:
? :true $!PIO.close()
but I know that's probably going a bit too far, and I'd like to think it's
too late for that kind of feature request.
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