Having said that, Java is a typed, safe OO language, and that alone, I contend, already makes it close in spirit to ML (in particular, its structures/signatures). I think interfaces (and the ability to override methods like `equals` are pretty close to abstract types. I also strongly disagree with your description of Java's parametric polymorphism being "botched", and certainly not that its "entire point" is defeated. That it can be circumvented is what makes code and data sharing between different languages with different variance models possible (compare to how badly that's done in .NET). So it's simply a matter of what requirements are more important to you.
I can understand those that think that Java not being fully static or fully dynamic may defeat the whole purpose of what they like in their preferred approach. But I think that Java combines static and dynamic aspects in a rather unique and novel way, and the new module system is not different, combining in an interesting way both static and dynamic aspects.
The whole point to structures and signatures is abstract types. Mere value hiding can be achieved with let, which isn't exactly the pinnacle of typing: Scheme has it.
> I think interfaces (and the ability to override methods like `equals` are pretty close to abstract types.
Please do tell how you would make two or more instances of an abstract type in Java, in such a way that:
(0) The client is aware that that the two instances have a common type.
(1) The client is not aware of the representation.
If it's not possible, then Java doesn't have abstract types, period.
> That it can be circumvented is what makes code and data sharing between different languages with different variance models possible
And unsafe. (No, memory safety alone isn't safety.) If it's going to be unsafe, then I better at least get my money's worth in terms of performance, which is why low-level languages like C and Rust are the only ones worth FFI'ing to.
> I can understand those that think that Java not being fully static or fully dynamic may defeat the whole purpose of what they like in their preferred approach.
Java is fully dynamic. “Type checking” in Java is basically a mandatory linter.
By having two implementations of a common interface, like `ArrayList` and `LinkedList` both implementing `List`.
> And unsafe.
It seems like you're defining "safe" to be precisely what the languages you like provide, no more and no less. I can say that ML and Haskell are unsafe because they don't statically forbid erroneous behavior at runtime, like a sorting function that doesn't sort (or doesn't terminate). Java has no undefined behavior. In fact, it is completely unknown how much safer -- if at all -- is ML than Java in practice.
> If it's going to be unsafe, then I better at least get my money's worth in terms of performance, which is why low-level languages like C and Rust are the only ones worth FFI'ing to.
Of course it's a matter of specific requirements, but I think you get more than your money's worth in terms of performance in Java, and having decades of experience writing huge multi-MLOC programs in both Java and C++, I'm convinced that it takes significantly less effort to get a well-performing large Java app -- especially if it's concurrent -- than a C++ app, even though you could surpass Java's performance given considerable additional effort. In any event, I think that the success of the JVM shows that many people find supporting it to be worth it.
> Java is fully dynamic. “Type checking” in Java is basically a mandatory linter.
This is simply untrue. Java is mostly type safe. If you have a variable of type `Foo` in your program, it cannot reference an object of a type that is not `Foo` at runtime. You are right that this does not extend to generic types, but only if -- 1. you've intentionally tried to circumvent the type, or 2. you've fallen victim to an obscure bug that was found recently, and is very hard to reproduce accidentally.
