[9rx]

> By forgetting.

Like in the same way you might forget to write pattern matching code? I mean, that's possible, but the checks and balances are going to let you know. In light of that, what is the significance of forgetting for the few seconds, if that, before getting notified of your forgetfulness? That's not a real problem.

> Pattern matching (with algebraic data types/enum/unions) helps because it forces you to check the error.

Checking the error alone is pointless. You need to also do something with the error, and pattern matching does nothing to help you with that. But that's what tests are for, there to help you with exactly that.

And since your code needs the right branching strategy to get to the point of doing something with the error as validated against the documentation, you also know that your branches are present and working as documented. You cannot possibly forget them after applying the checks and balances. How could you?

All you can really forget to do, maybe, is to document what the program is supposed to do. But in that case the program isn't supposed to do what you forgot to add anyway. Anything missed is undefined behaviour. If you have forgotten to consider what you want your program to do, no language can help you with that!

[madeofpalk]

In Go you can forget to call a function with the correct arguments, and it will not compile, right?

[9rx]

No, definitely not. The compiler couldn't care less if your arguments are correct. Consider:

   func cleanupTemporaryDir() {
       os.RemoveAll("/")
   }

You might have some very unhappy users if you ship that. Of course, as you would have documented your intended behaviour, the mistake is going to get caught when you run your tests, making it abundantly clear that you screwed up before bad things happen. Like before, you're not going to end up out.

Sure, a language with a deeper type system can place restrictions on what kinds of values you can pass in. "/" would be prevented by the type checker, letting it be known as you type and not later when you run the tests. That is nice. Nobody is going to deny that. But this act as if it is the only thing that will save you is completely disconnected from reality. Our world does not exist in this imagined vacuum where when one thing doesn't exist nothing does.

[richbell]

> Like in the same way you might forget to write pattern matching code?

This is a lengthy response to seemingly ignore, or miss, the point being made.

It is literally impossible to "forget" if you have pattern matching + algebraic data types/enum/unions. Conversely, it is possible and easy with Go.

Nothing you have said acknowledges this.

[9rx]

> It is literally impossible to "forget" if you have pattern matching + algebraic data types/enum/unions.

No, it's entirely possible to forget. That should be obvious. It is a functional necessity for you to be able to forget as you can only type so much at a time. You cannot possibly write code to call a function and perform pattern matching on the result at the exact same moment in time. There fundamentally has to be a period of time where the work will be incomplete, which opens the opportunity to not finish. It should be abundantly apparent to you that that you can forget to finish what you started in such a scenario.

Your checks and balances will alert you of your forgetfulness, but that's true of all languages. The biggest risk is that you will forget to define behaviour. But if you fail to do that, you've got problems even in languages with pattern matching and associated types. ADTs/enums/unions/pattern matching. are not sufficient to define behaviour. Not even close.

Like you said, pattern matching only helps you with checking errors. But there is no reason to check errors in the first place if you don't do something with the error, and for that you need to document what the error condition means for the user. Otherwise you have undefined behaviour. And once you've documented the behaviour, the error checks are confirmed for free anyway. You can't forget. The checks and balances will make it known, spectacularly.

What, exactly, are you trying to accomplish by overselling what is already a fantastic feature by its own merits on the basis of something that isn't at all realistic? If you want to get developers excited about the feature, there are way more compelling attributes to extol!

I have read this exact claim before, for what it is worth. Did you end up here simply because you repeated what you saw elsewhere without actually thinking about it?

[jsnell]

The distinction you're not acknowledging is that with pattern matching + algebraic data types you can't do anything with the payload without handling the error case. (You need to write a pattern match to extract the value, and the match needs to be exhaustive.)

With a separate error value, like in Go, that's no longer the case. The code for handling the error and the code for doing something with the payload are totally separate, and don't both need to be present.

[9rx]

What is to be acknowledge, exactly? By Go convention, values are to always be "useful", so the error is only significant if you need to use the error value for some reason. They are not logically intertwined like you have postulated.

Consider:

   func GetData() (*Data, error)

Both returned values are independently observable. Unless you need the error value for your particular situation, the Data variable contains everything you need to know. You can otherwise ignore the error value. Likewise, if all you need is the error value, you can ignore the Data value.

Success/failure values are logically intertwined by convention in some other languages, but you can't reasonably take idioms from other languages and slap them down on Go like that. Just as you cannot reasonably do so in reverse. Different languages express things differently. That's what makes them different.

Is that the disconnect here? That you believe all languages share the exact same idioms?

[jsnell]

No, all languages don't need to share the same idioms.

But you've been making arguments like the following:

> Like in the same way you might forget to write pattern matching code?

> No, it's entirely possible to forget. That should be obvious. It is a functional necessity for you to be able to forget as you can only type so much at a time. You cannot possibly write code to call a function and perform pattern matching on the result at the exact same moment in time.

And that is just disingenous. That's not you having a different opinion on something that's a matter of taste. That's you repeatedly trying to suggest that both forms of error handling are equally likely to suffer from somebody accidentally failing to handle the error.

And obviously that's not true, exactly because the returned values are logically separate in Go and aren't in the other lanuages. That is, in typical Go code, if you assign the error to err but omit the if err != nil {} boilerplate, the code will typically compile. (It'll compile, because the error variable is basically always named err, and most functions will have other references to that variable, such that the "unused variable" compiler diagnostics don't trigger.)

[9rx]

> the code will typically compile.

It may compile, but won't pass the test. Are you under the impression that a developer suddenly becomes blind after compilation and somehow magically won't see that the test failed? That doesn't happen. How are you going to forget? In reality, your forgetfulness is going to be made loud and clear. –– We offered a challenge to another account. He failed miserably, as did I, but maybe you can do better? https://news.ycombinator.com/item?id=42865349

And, before you even think it, no, you cannot skip that test in another language with pattern matching. There is nothing pattern matching can do to help you with what it is testing. It should be obvious to you that even if you do successfully pattern match, you might, for example, "forget" to return the right value. The documentation and additional checks and balances are required either way. The type system does not save you here.

And, before you even think it, no, "but what if I am a dummy who doesn't understand his tools or how to program???" doesn't work either as if you are that dummy then you aren't going to use the right types to activate the pattern matching semantics of which we speak, so pattern matching is not going to notice anyway. There is a necessary assumption in this discussion that you understand the tools, idioms, and software engineering in general. We cannot even meaningfully talk about pattern matching alone without that assumption.

So, how are you going to forget, exactly? You won't. This isn't a real thing. Pattern matching is cool, though, with many real benefits. It is funny that someone decided to focus on a made up benefit instead of what makes it actually great. But this is a commonly repeated trope so I'm sure we got here because he blindly repeated it without thinking about it for even a millisecond.

[richbell]

> I have read this exact claim before, for what it is worth. Did you end up here simply because you repeated what you saw elsewhere without actually thinking about it?

I can't tell if you're being intentionally obtuse. It behooves you to research the topic being discussed, instead of writing long-winded snarky posts.

It is not worth continuing this discussion unless you can demonstrate, with explicit code examples, what you think we're talking about, and why you believe it is incorrect.

[9rx]

Okay, sure. Here is an explicit code example:

     func foo(bar func() error) bool {
          err := bar()
          if err != nil {
               return true
          }
          return false
     }

     func TestFooReturnsTrueWhenBarReturnsError(t *testing.T) {
          if foo(func() error { return nil }) {
               t.Error("expected foo to return false")
          }
          if !foo(func() error { return errors.New("error") }) {
               t.Error("expected foo to return true")
          }
     }

Now it is your turn. Modify the body of function foo to remove the error check as you imagine it would be if it were forgotten.

This https://go.dev/play/p/k8zDQj5knaj is what I envision you are talking about, but clearly that cannot be it. As you can see it loudly proclaims that I "forgot", making this forgetfulness idea you have come up with impossible. So, what it is that you actually have in mind?

[richbell]

That is not what is being discussed and you know it.

Provide an example backing up your claim regarding pattern matching + union types:

> Like in the same way you might forget to write pattern matching code?

[9rx]

> That is not what is being discussed and you know it.

That is exactly what is being discussed. Why would the topic arbitrarily change? In case you have forgotten, my literal question/assertion was:

"How would you forget, exactly? Your tests are going to blow in your face should you ever leave out an entire feature from the implementation."

Go on, show us: How would you forget?

> Provide an example backing up your claim regarding pattern matching + union types:

Uh... Okay. Sure? Strange request, but here is an example in CrabLang that meets your ask:

    let result = foo();
    match result {
        Ok(value) => println!("Result: {}", value),
    }

There you go. I forgot to check the error.

Like I said in the full comment that you quoted from, you'll soon recognize your forgetfulness once you apply your checks and balances, but for that brief moment in between it is possible to forget. It must be that way else it would be impossible to input the program. If that's what you think we're talking about... Why? And let me ask again like I did in the comment you quoted from: What is the significance of that? If you had carried that quote through you'd also see: "That's not a real problem." I stand by that. Why not you?