Comment by sunnydiskincali | Hacker News Reader

Comment by sunnydiskincali | Hacker News Reader

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sunnydiskincali

> You wrote a lot of words to say very little.

Substantiate this.

> weird name choice but whatever

I don't think this kind of snarky potshot is in line with the commentary guidelines. Perhaps you could benefit from a refresher?

https://news.ycombinator.com/newsguidelines.html#comments

> Thanks to subtyping, no contortion needed

I see the same degree of contortion, actually. Far more noisy, at that.

> No need to use 7 more lines to create a separate, unrelated type.

You're still creating a type, because you understand that a sum-type with a different set of cases is fundamentally a different type. Just like a class with a different set of inheritance is a different type. And while it's very cute to compress it all into a single line, it's really not compelling in the context of readability and "write once, use many". Which is the point you were making, although it was on an entirely different part of the grammar.

> Great analogy, except for the fact that someone from the Java team explicitly said they're drawing inspirations from ML.

ML didn't invent ADTs, and I think you know it's more than disingenuous to imply the quotation means that the type-system in Java which hasn't undergone any fundamental changes in the history of the language (nor could it without drastically changing the grammar of the language and breaking the close relationship to the JVM) was lifted from ML.

> Substantiate this.

You never gave an example how sum types in Java/Kotlin cannot do what "real" sum types can.

>> weird name choice but whatever

> snarky potshot

Sorry that you read snark. What I meant was "I find naming this 'Bound' weird. But since I am translating your example, I'll reuse it".

> You're still creating an unrelated type

How can a type participating in the inheritance hierarchy be "unrelated"?

> I see the same degree of contortion, actually. Far more noisy, at that.

At this point I can only hope you're a Haskeller and do not represent an average OCaml programmer.

PS rereading this I think "hope you're a Haskeller" might be read as an insult. That's not my intention, here's why I mention Haskell.

1. It's THE other language with a type system based on HM.

2. Variant constructors as functions. OCaml does not do that, Haskell does (slightly more elegant). This hints sunnydiskincali is more familiar with Haskell than OCaml.

3. I was confused by `type shape = S.shape`. How does `RemovePoint(Shape).shape` has the `Point` case removed then? I tried that on a REPL ^1 and it didn't even compile. Again, syntax errors hinting at Haskell experiences.

Well now I've written so much I may as well do a point-by-point refutation: ^2

> you create the ability to side-step exhaustiveness

Big claim, sounds scary to someone not familiar with sum types. But Java/Kotlin both enforce exhaustiveness. You could have provided an example in your second response, instead you dump a bunch of code that does not compile.

> Sure you can, that's just subtyping.

Then you followed up with an example that is not subtyping, but an unrelated type of a new set of new values.

> This is doing things quick and dirty. For this trivial example it's fine

This is not fine. I undersold the verbosity of your "quick and dirty" solution saying "7 lines". To actually work with those two types, the pair of conversion functions `Shape.shape -> Bound.shape option` and `Bound.shape -> Shape.shape` is needed.

> They're not similar at all.

~100 words in the paragraph, gestures to formalization, yet never explained how sum types implemented as sealed inheritance cannot be "enforcing valid program-states at a type-level". Thus my comment "a lot of words to say very little".

> You're still creating a type

I see you removed "unrelated" in an edit. The statement is now accurate but pointless. Of course I need to create a type, how else can I use the type system to say "this function won't return a point"?

> disingenuous to imply the quotation means that the type-system in Java ... was lifted from ML.

It would be more than disingenuous, colossally stupid even, if I did imply that. The wrongness would be on the level of claiming "English and Japanese are in the same language family".

Your cognate/false friend analogy is much smaller in scope, just like Java taking sum types (implementing them as sealed inheritance) from ML.

1: https://ocsigen.org/js_of_ocaml/toplevel/

2: https://xkcd.com/386/

I'm very embarrassed to say this. Those code examples weren't non-compiling OCaml, but valid SML. Once I remembered the existence of the language (in my defence it was never mentioned in the thread), I managed to compile the code, and confirm my suspicion:

`val point: Bound.shape = Shape.Point` type-checks, because `type shape = S.shape`. To drive the point home, so does

    val DoesNotReturnPoint : Shape.shape -> Bound.shape = fn x => x

So the module example does not show "this function won't return a point" as one would have hoped.

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