EDIT: also, strictly speaking, Rust doesn't use Hindley-Milner, and we don't have parametric polymorphism.

  struct Person<T> {
    age: T,
  }

There's also more minor things like https://github.com/rust-lang/rfcs/pull/1210#issuecomment-179...

If you ask all the developers out there to describe parametric and ad-hoc polymorphism I think a vast majority would give the example of a type parameter (e.g., Java generics or C++ templates) for parametric polymorphism and Java interfaces or Haskell's classes for ad-hoc polymorphism. I can even quote directly from Pierce (Types and Programming Languages):

> Parametric polymorphism, the topic of this chapter, allows a single piece of code to be typed "generically," using variables in place of actual types, and then instantiated with particular types as needed. Parametric definitions are uniform: all of their instances behave the same.

I think Rust and the aforementioned languages fit this definition. Outside of a specific compiler issue, claiming otherwise seems to only confuse the issue, especially for those just casually reading and not familiar with programming language theory.

In practice it is often useful to drop our demands for rigour by a bit. But any reasonable definition of parametric polymorphism _has_ to exclude C++ templates.

C++ templates are much closer to the definition of ad-hoc polymorphism.

My practical less-than-rigorous rule-of-thumb for parametric polymorphism amounts to something like: whenever Wadler's Theorems for Free paper applies. https://ttic.uchicago.edu/~dreyer/course/papers/wadler.pdf

Theorems for Free means that eg the type of the identity function (forall a . a -> a) guarantees that even if you supply it a bool, it can't magically turn into an implementation for `not`, or multiply all integers by 2.

Which doesn't mean it's terrible to get it wrong, just want to be clear about what Rust does and does not have. It is important because these kinds of definitions either hold or they don't; "sorta kinda mostly parametric" isn't the way folks tend to think about this. Which makes sense, because they're interested in proofs and formal definitions.

Yes, Pierce is great! But the issue is:

> all of their instances behave the same.

This is not true in Rust, as shown in my comment and the other replies. We have accepted APIs that break this property, and we have other language features on the way that break this property.

    fn foo<T>() -> usize {
        std::mem::size_of::<T>()
    }

    foo::<u8>(); // 1
    foo::<u16>();  // 2

The _behavior_ of this function is the same for all types, the _output_ is different. That is, for all types, the function body is the same. Maybe there is a more abstract definition of parametric polymorphism you are using, but as I said above, this seems pedantic.

    fn foo<T>() -> usize {
        let x = std::mem::size_of::<T>();
        if x % 2 == 0 {
            panic!();
        }
    }

    foo::<u8>(); // 1
    foo::<u16>(); // panic

> this seems pedantic

The first code example is merely the simplest demonstration, in the wild I would expect lots of `size_of` in generic contexts to result in type-dependent behavior somehow.

I'm not saying this is necessarily a very bad thing, nor do I have strong opinions on the usefulness of strict parametricity (which AFAIK Haskell doesn't have either). But in discussions relevant to parametricity, it's useful to know the ways a given language can subvert it (and Rust will further encourage it to be subverted, once the specialization feature is developed).

In practice Haskell seems to have pretty strong views on enforcing parametric polymorphism, doesn't it?

Haskell gives you ad-hoc polymorphism via typeclasses and there are also existential types and GADTs etc, if you need those. But once you declare something to abide by parametric polymorphism, you are expected to keep your end of the bargain.

(Yes, you could violate the pact via some unsafePerformIO trickery, but that's considered bad form.)

If you functions routinely violate those limits as a matter of course, those guarantees are useless.

I'm all for abusing notation and terminology a bit when it makes sense in practice, but loosening our definitions too much risks making them useless, too.

In practice in Haskell, I often only need a helper function for eg integers, but when the implementation allows, I will give the function the most parametric-polymorphic type that fits, because that makes the readers job easier:

Just like an invocation of `filter` is easier to read than a for-loop, because `filter` is strictly less powerful than the loop.

(In addition, the more general type serves to give the compiler a hint, so it can yell at me in case I accidentally do an operation on the integer that I didn't mean to.)

> However, in 2020, the premier system’s language is surely Rust.

Yesterday I was speaking with a friend who runs a small company doing contracted embedded programming (the embedded OS is often Linux but often not) and he'd never even heard of Rust. Maybe it's a little lower level than what's meant by "systems" here but still, the article's statement is just delusional.

I can go to Green Hills and get a contract that guarantees their compiler will be available and supported for my target platform for the next 10+ years. Rust is still a moving target with a single implementation, and no (present) way to get the guarantees needed for the embedded domains I've been involved in. I'd like to see Rust experimented with there, but it won't be the "go to" language for quite some time.

Absolutely. I've said it before, I will say it again, Rust will not be taken seriously as a systems language until it is specified. As I understand it years ago I was laughed at for this, but it is underway. I am grateful for this.

I forgot to preface my statements with I Love Rust, or, moreso, I actually love OCaml, and I love OCaml inspired languages, and I would love to write an OS in it (save ReactOS).

That being said, the desire to label it as the "premier systems language" (and no fault of the author, many before have tried to say this) is entirely not grounded in any sort of reality.

Whether or not these advances make a difference (positive or negative) in production is different question, but I'd rather not use "how much is a language used", as an inherent quality metric for a programming language. Otherwise, I fear we might all end up doing old-school Java, Javascript, Visual Basic and ABAP.

Define quality. Because what I've realized with the PL-elitist crowd is this almost always boils down to "the ability to be expressive" which is fine but it certainly isn't a complete metric, and, to borrow a common refrain, we've had expressive languages in the 70's as well, we've had s-expressions for a while now. What about other metrics, such as "ability for mass amounts of programmers to program the computer to do the correct thing?" and "ability for programmer to maintain said program?" -- you know, real world quality. My point is, people's usual quality metrics are often incomplete or narrowly defined.

In either case, if Go is so primitive, then why didn't the 70s produce a language like Go? Why did developers who created languages, operating systems, and systems software in the 70s not make Go until the 2000s (you do know who created Go, right?)

I just don't buy this argument, especially having used those "advanced" type systems for many years, sorry.

But all that says is that the magic of Go isn't in the type system. The couldn't produce-it-until-the-2000s isn't in the type system. The thing that makes Go more used in the real world than Haskell isn't the sophistication of the type system.

I don't see much to argue with in those claims.

My second point was that the popularity of Go (or any language) does not mean that it is inherently a good language, where good can mean, productivity, defect rate, .... Adoption of a language depends on many things, I believe quality of the tools, availability of libraries, and good old marketing (the Google aura around Go has helped in adoption) are often more important. The effort to make an initial, crappy, proof-of-concept is in my experience often decisive for the choice of language. The cost of long term maintenance (where a good type system might bring value) is rarely considered.

For Go, it also hasn't hurt that some of the core developers where being paid by Google to work on it.

The metric of the "ability for mass amounts of programmers to program the computer", is indeed a very relevant one, and I think Go shines there. When reading Go code, I typically find it easy to understand what the goal of the code is. However, "to do the correct thing", is often less of a success: there are off-by-one error and corner cases that have bugs, and reimplementations of the same basic logic. If you have a lot of developers available, you simply have them fix these issues, and your Go project becomes a success.

My point is, that in this scenario, the language itself is of minor importance: success is determined by the fact that you have access to a large pool of relatively cheap labor of reasonable quality (Google or VC funded startups are perfect examples). A 20 or even 50% productivity gain by having a "better" language would simply not matter for the outcome, certainly not if it takes your labor longer to get up to speed.

So, in that context, compared to the alternatives, the quality of Go is relatively high. But I do think that, if during the design of Go they had taken a couple of basic concepts from ML like sum types, polymorphism, and a decent module system, they would have ended up with a language that would make the current Go look unproductive and poor quality, even in that same context. It wouldn't make a difference to Google, but it would make the life of many a developer a little bit more productive and joyful.

And yes, I do know who created Go, but arguments by authority carry little weight.

I have the opposite experience. At a micro-level you might be able to tell what a line of Go code is doing, like manipulating this variable into that state etc, but it's such a tedious language that drowns the reader in code that it can be very hard to see the forest for the trees.

As an example of a deliberately simple language that mostly easy to read, I would perhaps cite Erlang.

In any case, I agree wholeheartedly that Go would benefit from sum types. (Though given the weak type system otherwise, you couldn't even implement a useful `Maybe` in Go. You'd really want parametric polymorphism to make sum types shine.) A way to express immutability would also have been welcome, especially given that they pride themselves on concurrent programming.

The "PL-elitist" crowd looks at programming languages from a computer science perspective, while the "PL-pragmatist" crowd (for lack of a better term) looks at it from a workplace perspective. At least that's how I see it.

In other words, one group writes tooling and libraries; the other writes business applications using said tooling and libraries.

One paradigm invites complex, highly expressive code as to minimize the chance of unforeseen errors (even if just by having a smaller codebase), and as to provide a clean and powerful interface that "does more with less".

The other invites simple, highly maintainable code as to minimize the training overhead of new employees and the chance that their lack of rigor might end up accidentally introducing or reintroducing bugs. Furthermore, a simpler language means that new teams can hop onto a pre-existing project faster, because they don't have to scrutinize each LOC to the same extent.

I might be wrong on any or all of this, but that's how I perceive it.

There are other languages I can take out of the bag like Mesa/Cedar, Interlisp-D, Smalltalk-80, although they are already on the 80's borderline, which then also brings Ada, Standard ML and Object Pascal into the picture.

That may offer consolation to those who think that certain languages are the best, and who wonder why those "best" languages are used so little. But I don't think it's true. I don't think programmers are stupid, ignorant, or sheep. I think if a tool offers them advantages, they'll use it.

Perhaps I should qualify: significant advantages. There is a cost to switching. The switched-to language has to be enough better to pay back the cost.

I remember what Sun did with Java back in the day. No, I do not agree that Go has been massively marketed.

I will admit, however, that Go was created and supported by Google, and that mattered. It mattered, not in the publicity, but in the tools and libraries (and maybe even in the tutorials).

So your point is because Java has been marketed more then Go that Go is not massively marketed? If you take the set of all languages and would make a sorted list of how many hours and dollars where spend to market it then I would be very, very surprised to not see Go in the top 5.

Advertisement is a subset of marketing. Back in the day when Go was "new" You saw daily posts on many programmer focused communities about it. Google bankrolled the entire development of Go. Blogposts of many googlers talking about the language. Google sponsored Go events. The positive image of Google itself at the time of Go initial introduction.

You try to weasel me towards C# and Java when those are not two language I even have mentioned. But since you want to hear about. Yes both of these were also heavily marketed.

Or, if the big company doesn't do anything more than is done for other languages (Rust, say), what difference does it make? Is Rust marketed in the same way Go is? Per your definitions, I would say yes, even though the Mozilla Foundation isn't a big company.

But then, is Haskell marketed in the same way? I see lots of posts on it, at least here. Lots of blogposts on it. But there's no big company, or even foundation, behind it. Is that marketing?

Why do you define a set of actions as marketing when people who work for Google do it, but not when others do it?

Go have limited capabilities type system. C have limited capabilities type system. Both are quite successful. If talking about C I didn't shown "intellectual superiority", maybe it would be incorrect label if I where to talk about Go?

It's just that in Haskell you have to write fewer tests to be sure you did it right, because for many kinds of mistakes you could have made, the compiler can yell at you.

The other advantage of nicer types is that they serve as part of the documentation. Exactly because the types can constraint the behaviour of implementations more than in Go. So the reader can make more valid assumptions from the type alone.

Hoogle uses those types to give you a truly extra-ordinary way to search the Haskell libraries via types. That approach would be almost useless in Go, and you have to fall back to searching via keywords etc only.