I’d rather have exceptions thrown for a simple reason: errors as values make it too easy to ignore them. You have to explicitly check for errors and take a different course of action rather than your program do it for you.

If I’m parsing a JSON and there’s a syntax error, I definitely DO NOT want my program to keep running and risk entering an undefined state because a function somewhere is not checking the error value. An exception forces the consumer of a function to handle it, or have the program fail. The point the article makes about “not being able to tell where the error came from” is bogus since there’s a stack trace.

IME the default behavior of a program when facing an unhandled error should be to stop execution. There are a million things that could go wrong. We can’t cover them all and we shouldn’t expect consumers to check for errors on every line when they might not even be able to handle them: that’s where bubbling up errors really comes in handy. And making it happen when they’re just values require all intermediate functions to check for them.

If you wrote the type signature of get_user as tuple[User, None] | tuple[None, Exception], the assertion would not be necessary and the type checker wouldn’t complain.

They forgot the Erlang approach: throw exceptions but never catch them. If you are throwing an exception either your code is wrong or your system is bad. In either case, you should crash violently and let another instance handle the retry.

I’ve actually been experimenting with this on and off for about a year now. My team and I also came to the conclusion that unions were the best approach but we hadn’t considered using match. Might give that a shot if any type systems start supporting it better

Rusty python

The words errors, go and usefull do not match in my brain.

If there is a way not to implement error handling, it would clearly be go’s implemenation.

If only python had a throws keyword like in Java. They got that right at least.

I don’t really see the point of this approach. The whole bane of programming in low level languages like C is that you had to write one line of code, then 10 lines of error management for that line. Repeat until 500 lines, potentially with gotos in order to rollback previously successful operations. The result was that C was mostly error handling of function calls, and the ways to return such errors were hackish. Add reentrancy and multithreading requirements and it became a mess.

The idea of exception throwing is to forget all of this and have a separate channel where exceptions conditions flow, so the code is mean and lean and just does things, and when something goes wrong it throws a fit. If someone understands and manages that fit, great, there will be a specific handler for that, otherwise it won’t. An exception is never ignored. Either it’s handled or it reaches the top and stops the whole thing. With value as errors, the default is exactly the opposite.

So I don’t really see a big case for going back to the old days of errors as values, because it really, really sucked.