16:34 <abelard> hey guys, I have a question

16:34 <abelard> what is error exactly? is it a primitive?

16:51 <jemc> abelard: in the runtime, `error` is just an unwinding of the stack to the nearest containing `try` block's `else` clause

16:53 <jemc> at compile time, it is a "jump away" instruction that makes the compiler enforce that either there needs to be a `try` block containing the error or the method signature needs to be "partial" (with a question mark), with the enforced assumption that there is another `try` block somewhere up the call stack

16:53 <abelard> ah, I see. thanks jemc

16:54 <abelard> by the way, if I'm handling an error, is printing from the main actor a more desirable behavior than printing from the actor in which the error occured?

16:55 <jemc> the best practice depends on a lot of factors - it can be different depending on the nature of what you're building, what your goals are, and what kind of error you're handling

16:55 <abelard> basically I want to print an error and exit

16:56 <abelard> to print from main, I'd have to return an enum so main would know what to print

16:57 <jemc> for panic/abort style of error handling, it's become a sort of common practice to use FFI to `printf` and `exit` - here's an example of what I use for that: https://github.com/jemc/ponycc/blob/master/ponycc/unreachable/unreachable.pony

16:58 <jemc> if you want something cleaner, or if you have other cleanup that needs to happen on exit, I'd suggest you take a different approach:

17:00 <jemc> introduce a "custodian" actor that keeps a handle on everything that needs to be `dispose`d for an exit (like any open network sockets), and also give it the capability to print what you want to print

17:01 <jemc> if you want to use standard library stuff for that, you could probably use bureaucracy.Custodian (https://github.com/ponylang/ponyc/blob/master/packages/bureaucracy/custodian.pony) and logger.Logger (https://github.com/ponylang/ponyc/blob/master/packages/logger/logger.pony)

17:01 <jemc> and maybe create a composite actor in your program that contains both

17:02 <jemc> then you have to share a reference to that composite actor, so that any part of your program that needs to "abort" can do so

17:02 <jemc> that's the cleaner, more actor-oriented way to do a soft abort ^

17:03 <abelard> wow thanks jemc!

17:03 <abelard> I'll try to use a custodian

18:08 <abelard> how do I create a mutable string?

18:26 <SeanTAllen> abelard: https://playground.ponylang.org/?gist=66693eba34f38c78574d34ecc0efe8dc