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by kibwen 546 days ago
> show the call stack where they occured. And we have a name for that...exceptions.

Getting a stack trace isn't a distinguishing feature of exceptions; stack traces predate the notion of exceptions. The distinguishing feature of exceptions is that they're a parallel return path all the way back up to `main` that you can ignore if you don't care to handle the error, or intercept at any level if you do. For some contexts I think this is fine (scripting languages), and for other contexts I think that being forced to acknowledge errors in the main return path is preferable.
2 comments
danenania 546 days ago
I think a lot of it is psychological. Being forced to ask yourself "what do I want to happen if there's an error here?" every single time seems to go a very long way. If the answer is "ignore it" or "bubble it up" then fine, but at least you considered and explicitly answered that question rather than totally forgetting that an unhappy path exists. Default consider vs. default ignore.
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ekimekim 546 days ago
That's interesting. To me stack traces + default pass up the stack are the distinguishing features of exceptions.

Suppose we had a version of the ? operator that automatically appended a call stack to the error value returned. Are you saying that that's not "an exception" because I still need to write ? after each falliable function? Or because it's still part of the return type? Or is it specifically only an exception if it works via stack unwinding?

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kibwen 545 days ago
If we're making a distinction between "exceptions" and "errors as return values", then that implies that exceptions are not return values. And so the question to ask to identify each one is: is the error treated the same as a returned value would be? IOW, if it shows up in the usual return type location in a function signature, and if calling this function plops the value into my lap the same as it would for any other value, then it's errors-as-values. Whether or not stack unwinding is used and whether or not a stack trace is provided is an implementation detail. Note that C++ certainly has exceptions, and yet getting a stack trace from them is nontrivial.
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