[perl #131118] [RFC][@LARRY] Implement a way to propagate exceptions in Junctions
On Fri, 07 Apr 2017 10:08:54 -0700, comdog wrote: > Consider this junction which you probably shouldn't make but you know > will happen in the hands of users: > > any( 5, 'flarg' ) == 5 > > Despite having an element that satisfies the condition, it blows up > because one of them doesn't: > > > any(5, "flarg") == 5 > Cannot convert string to number: base-10 number must begin with > valid digits or '.' in '⏏flarg' (indicated by ⏏) > in block at line 1 > > But, it should't matter that what happens with any other parts of the > junction if at least one of them satisfies the condition. You could, > for instance, evaluate that differently so the new junction looks > something like this: > > any( True, Failure ); > > But, I don't think it should evaluate to another junction at all. The > comparison operator should evaluate to a Boolean. That Failure will > never matter because it's equivalent to False. Thank you for the report. However, I'm going to reject the ticket. As previous replies mentioned, there's no problem with Failures in a Junctions, they work as any other value. The actual explosion in OP's code happens when one of the Failures—created when 'flarg' was coerced to Numeric—is used as a value for the purposes of evaluating the `==` op with it. That's when the Exception gets thrown. I'm unsure if one of the suggestions was to catch such exceptions and turn them into Failures again... If it were, it's not a good idea, since Junctions are not meant to be well-introspectable and just silencing exception like that is bound to end in tears. Some of the other suggestions were to make `try` Junctionable and stuff a Junction into $! variable. If that's possible to do at all, IMO it should be done as a trial in a module first, to evaluate usability and any issues with the compatibility with core code. Lastly, I added a 'Failures and Exceptions' section to Junction docs[^1] that explains the issues raised in this ticket as well as shows some of possible ways to attain the goals, if really necessary. [1] https://github.com/perl6/doc/commit/7628708384bdc049d74c997fc2059cf57fcf5a57
[perl #131118] [RFC][@LARRY] Implement a way to propagate exceptions in Junctions
On Fri, 07 Apr 2017 10:08:54 -0700, comdog wrote: > Consider this junction which you probably shouldn't make but you know > will happen in the hands of users: > > any( 5, 'flarg' ) == 5 > > Despite having an element that satisfies the condition, it blows up > because one of them doesn't: > > > any(5, "flarg") == 5 > Cannot convert string to number: base-10 number must begin with > valid digits or '.' in '⏏flarg' (indicated by ⏏) > in block at line 1 > > But, it should't matter that what happens with any other parts of the > junction if at least one of them satisfies the condition. You could, > for instance, evaluate that differently so the new junction looks > something like this: > > any( True, Failure ); > > But, I don't think it should evaluate to another junction at all. The > comparison operator should evaluate to a Boolean. That Failure will > never matter because it's equivalent to False. Thank you for the report. However, I'm going to reject the ticket. As previous replies mentioned, there's no problem with Failures in a Junctions, they work as any other value. The actual explosion in OP's code happens when one of the Failures—created when 'flarg' was coerced to Numeric—is used as a value for the purposes of evaluating the `==` op with it. That's when the Exception gets thrown. I'm unsure if one of the suggestions was to catch such exceptions and turn them into Failures again... If it were, it's not a good idea, since Junctions are not meant to be well-introspectable and just silencing exception like that is bound to end in tears. Some of the other suggestions were to make `try` Junctionable and stuff a Junction into $! variable. If that's possible to do at all, IMO it should be done as a trial in a module first, to evaluate usability and any issues with the compatibility with core code. Lastly, I added a 'Failures and Exceptions' section to Junction docs[^1] that explains the issues raised in this ticket as well as shows some of possible ways to attain the goals, if really necessary. [1] https://github.com/perl6/doc/commit/7628708384bdc049d74c997fc2059cf57fcf5a57
