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Postings from June 2020
On Sat, 27 Jun 2020 13:48:31 +0200
Paul Johnson <paul@pjcj.net> wrote:
> Summary: I'd love to get a very simple try/catch syntax in core as an
> experimental feature.
>
>
> I'm mostly happy with Syntax::Keyword::Try, especially with the
> enhancements described below made possible by being core. I don't
> really like "finally" as implemented and would be happy to leave it
> out of an initial core implementation.
I agree; see my other post just now about a LEAVE phaser.
> I don't need any kind of type system/matching initially and would
> suggest that anything in that area should be more general and
> shouldn't be considered for an initial implementation here.
Please lets not confuse "implementation" with "design". I would still
like to *design* what shape a type-matching part of the syntax would
look like, even if just approximately.
I don't want to start implementing a simple "catch all" version if it
turns out that design makes it hard to squeeze in the type stuff later
on. I want to know where the thing is heading, so we don't start off
going in the wrong direction.
> I don't
> really care what variable the exception ends up in in the catch
> block. Being fast would be nice.
>
> I think a simple syntax such as that described below is sufficiently
> clean that it should always work, whatever other bells and whistles
> may subsequently be added.
Yes I don't think the initial bits below were particularly contentious.
It's all the other bits about type matching/dispatch that make it
complicated.
Lets make a really concrete example: Here is some existing Perl code
that you can write right now, using plain ol' eval{}.
unless(
eval { somefunc(); 1 }
) {
my $e = $@;
if ($e isa X::SomeException) { say "Red" }
elsif($e =~ m/^Cannot do a thing /) { say "Blue" }
else { rethrow }
}
How would you see rewriting that in a hypothetical core 'try'? I
suggest for example:
use feature 'try';
try {
somefunc();
}
catch my $e (isa X::SomeException) { say "Red" }
catch my $e (=~ m/^Cannot do a thing /) { say "Blue" }
Which is non-ideal due to multiple `my $e` and those dangling binary
operators `isa` and `=~` just starting the parens there. They look a
bit ugly IMHO.
Can we find better?
--
Paul "LeoNerd" Evans
leonerd@leonerd.org.uk | https://metacpan.org/author/PEVANS
http://www.leonerd.org.uk/ | https://www.tindie.com/stores/leonerd/
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