- ~Exhaustive pattern matching~ it’s here!
- Algebraic data types
- Tail call optimisation
- Do notation
- Operator overload
Why not use another language? Well, the name “Java” guarantees buy-in at this point. Maybe it will eventually be a Trojan horse for ML :)
What does this mean? Well with generics we can have two libraries that know about Map<> and concrete types TypeA and TypeB and can interface type-safely using Map<TypeA, TypeB>.
What we can't do is have two libraries that know about TypeA and TypeB interface type-safely using a sealed type of TypeA and TypeB. Even without considering libraries, another use we may want to talk about a sealed type of TypeA and TypeC, but of course TypeA can only be in one of the sealed class trees.
The worst part is that Java already has a Union type that's only ever used in multi catch(ExceptionA|ExceptionB e).
One thing I'd have to check is the quality of IDE support for refactoring tooling. Refactoring operations for Java using IntelliJ almost always works and as I expect or better.
I somewhat suspect Java is locked into its current approach to variance, but gosh, I much prefer Scala's approach here.
[0]: https://typelevel.org/cats-effect/ [1]: https://zio.dev
As for others, without proper Monads, I doubt they would have much use.
It’s great for avoiding nulls, but you get excessive nesting with many isPresent checks. Do notation can fix this.
The language even provides a bind function, but no reasonable way to use it!